Backward-compatible integration of harmonic transposer for high frequency reconstruction of audio signals

Abstract

A method for decoding an encoded audio bitstream is disclosed. The method includes receiving the encoded audio bitstream and decoding the audio data to generate a decoded lowband audio signal. The method further includes extracting high frequency reconstruction metadata and filtering the decoded lowband audio signal with an analysis filterbank to generate a filtered lowband audio signal. The method also includes extracting a flag indicating whether either spectral translation or harmonic transposition is to be performed on the audio data and regenerating a highband portion of the audio signal using the filtered lowband audio signal and the high frequency reconstruction metadata in accordance with the flag.

Description

(19) *EP004756801A1* (11) EP 4 756 801 A1 (12) EUROPEAN PATENT APPLICATION (43) Date of publication: 10.06.2026 Bulletin 2026 / 24 (21) Application number: 26157566.6 (22) Date of filing: 19.03.2018 (51) International Patent Classification (IPC): G10L 19 / 26 (2013.01) G10L 21 / 038 (2013.01) G10L 19 / 22 (2013.01) G10L 19 / 24 (2013.01) (52) Cooperative Patent Classification (CPC): G10L 21 / 038; G10L 19 / 26; G10L 19 / 22; G10L 19 / 24 (84) Designated Contracting States: AL AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO PL PT RO RS SE SI SK SM TR (30) Priority: 23.03.2017 US 201762475619 P (62) Document number(s) of the earlier application(s) in accordance with Art. 76 EPC: 25210522.6 / 4 661 002 25156641.0 / 4 550 324 18770254.3 / 3 559 821 (71) Applicant: Dolby International AB Dublin, D02 VK60 (IE) (72) Inventors: • VILLEMOES, Lars 113 30 Stockholm (SE) • PURNHAGEN, Heiko 113 30 Stockholm (SE) • EKSTRAND, Per 113 30 Stockholm (SE) (74) Representative: Dolby International AB Patent Group Europe 77 Sir John Rogerson’s Quay Block C Grand Canal Docklands Dublin, D02 VK60 (IE) Remarks: This application was filed on 10.02.2026 as a divisional application to the application mentioned under INID code 62. (54) BACKWARD‑COMPATIBLE INTEGRATION OF HARMONIC TRANSPOSER FOR HIGH FREQUENCY RECONSTRUCTION OF AUDIO SIGNALS (57) A method for decoding an encoded audio bit- stream is disclosed. The method includes receiving the encoded audio bitstream and decoding the audio data to generate a decoded lowband audio signal. The method further includes extracting high frequency reconstruction metadata and filtering the decoded lowband audio signal with an analysis filterbank to generate a filtered lowband audio signal. The method also includes extracting a flag indicatingwhether either spectral translation or harmonic transposition is to be performed on the audio data and regenerating a highband portion of the audio signal using the filtered lowband audio signal and the high frequency reconstruction metadata in accordance with the flag. EP 4 75 6 80 1 A 1 Processed by Luminess, 75001 PARIS (FR) Description

[0001] This application is a European divisional application of European patent application EP25210522.6 (Applicant’s Reference: D17023EP06). TECHNICAL FIELD

[0002] Embodiments pertain to audio signal processing, andmore specifically, to encoding, decoding, or transcoding of audio bitstreams with control data specifying that either a base form of high frequency reconstruction ("HFR") or an enhanced form of HFR is to be performed on the audio data. BACKGROUND OF THE INVENTION

[0003] A typical audio bitstream includes both audio data (e.g., encoded audio data) indicative of one ormore channels of audio content, andmetadata indicative of at least one characteristic of the audio data or audio content. Onewell known format for generating an encoded audio bitstream is theMPEG‑4 Advanced Audio Coding (AAC) format, described in the MPEG standard ISO / IEC 14496‑3:2009. In the MPEG‑4 standard, AAC denotes "advanced audio coding" and HE-AAC denotes "high-efficiency advanced audio coding."

[0004] The MPEG‑4 AAC standard defines several audio profiles, which determine which objects and coding tools are present in a complaint encoder or decoder. Three of these audio profiles are (1) the AAC profile, (2) the HE-AAC profile, and (3) the HE-AAC v2 profile. The AAC profile includes the AAC low complexity (or "AAC-LC") object type. The AAC-LC object is the counterpart to the MPEG‑2 AAC low complexity profile, with some adjustments, and includes neither the spectral band replication ("SBR") object type nor the parametric stereo ("PS") object type. The HE-AAC profile is a superset of the AAC profile and additionally includes the SBR object type. The HE-AAC v2 profile is a superset of the HE- AAC profile and additionally includes the PS object type.

[0005] The SBR object type contains the spectral band replication tool, which is an important high frequency reconstruction ("HFR") coding tool that significantly improves the compression efficiency of perceptual audio codecs. SBR reconstructs the high frequency components of an audio signal on the receiver side (e.g., in the decoder). Thus, the encoder needs to only encode and transmit low frequency components, allowing for a much higher audio quality at low data rates. SBR is based on replication of the sequences of harmonics, previously truncated in order to reduce data rate, from theavailable bandwidth limited signal and control data obtained from theencoder. The ratio between tonal and noise- like components is maintained by adaptive inverse filtering aswell as the optional addition of noise and sinusoidals. In the MPEG‑4 AAC standard, the SBR tool performs spectral patching (also called linear translation or spectral translation), in which a number of consecutive Quadrature Mirror Filter (QMF) subbands are copied (or "patched" or) from a transmitted lowband portion of an audio signal to a highband portion of the audio signal, which is generated in the decoder.

[0006] Spectral patching or linear translation may not be ideal for certain audio types, such as musical content with relatively low cross over frequencies. Therefore, techniques for improving spectral band replication are needed. Brief Description of Embodiments of the Invention

[0007] A first class of embodiments relates to a method for decoding an encoded audio bitstream is disclosed. The method includes receiving the encoded audio bitstream and decoding the audio data to generate a decoded lowband audio signal. The method further includes extracting high frequency reconstruction metadata and filtering the decoded lowband audio signal with an analysis filterbank to generate a filtered lowband audio signal. The method further includes extracting a flag indicating whether either spectral translation or harmonic transposition is to be performed on the audio dataand regeneratingahighbandportionof theaudio signal using thefiltered lowbandaudio signal and thehigh frequency reconstruction metadata in accordance with the flag. Finally, the method includes combining the filtered lowband audio signal and the regenerated highband portion to form a wideband audio signal.

[0008] A second class of embodiments relates to an audio decoder for decoding an encoded audio bitstream. The decoder includesan input interface for receiving theencodedaudiobitstreamwhere theencodedaudio bitstream includes audio data representing a lowband portion of an audio signal and a core decoder for decoding the audio data to generate a decoded lowbandaudio signal. Thedecoder also includesademultiplexer for extracting from theencodedaudiobitstream high frequency reconstruction metadata where the high frequency reconstruction metadata includes operating para- meters for a high frequency reconstruction process that linearly translates a consecutive number of subbands from a lowband portion of the audio signal to a highband portion of the audio signal and an analysis filterbank for filtering the decoded lowband audio signal to generate a filtered lowband audio signal. The decoder further includes a demultiplexer for extracting from theencodedaudio bitstreamaflag indicatingwhether either linear translationor harmonic transposition is to be performed on the audio data and a high frequency regenerator for regenerating a highband portion of the audio 2 EP 4 756 801 A1 5 10 15 20 25 30 35 40 45 50 55 signal using the filtered lowband audio signal and the high frequency reconstructionmetadata in accordancewith the flag. Finally, the decoder includes a synthesis filterbank for combining the filtered lowband audio signal and the regenerated highband portion to form a wideband audio signal.

[0009] Other classes of embodiments relate to encoding and transcoding audio bitstreams containing metadata identifying whether enhanced spectral band replication (eSBR) processing is to be performed. Brief Description of the Drawings

[0010] FIG. 1 is a block diagram of an embodiment of a system which may be configured to perform an embodiment of the inventive method. FIG. 2 is a block diagram of an encoder which is an embodiment of the inventive audio processing unit. FIG. 3 is a block diagram of a system including a decoder which is an embodiment of the inventive audio processing unit, and optionally also a post-processor coupled thereto. FIG. 4 is a block diagram of a decoder which is an embodiment of the inventive audio processing unit. FIG. 5 is a block diagram of a decoder which is another embodiment of the inventive audio processing unit. FIG. 6 is a block diagram of another embodiment of the inventive audio processing unit. FIG. 7 is a diagram of a block of an MPEG‑4 AAC bitstream, including segments into which it is divided. Notation and Nomenclature

[0011] Throughout this disclosure, including in the claims, the expression performing an operation "on" a signal or data (e.g., filtering, scaling, transforming, or applying gain to, the signal or data) is used in a broad sense to denote performing the operation directly on the signal or data, or on a processed version of the signal or data (e.g., on a version of the signal that has undergone preliminary filtering or pre-processing prior to performance of the operation thereon).

[0012] Throughout this disclosure, including in the claims, the expression "audioprocessingunit" or "audio processor" is used in a broad sense, to denote a system, device, or apparatus, configured to process audio data. Examples of audio processing units include, but are not limited to encoders, transcoders, decoders, codecs, pre-processing systems, post- processing systems, andbitstreamprocessing systems (sometimes referred toasbitstreamprocessing tools).Virtually all consumerelectronics, suchasmobilephones, televisions, laptops,and tablet computers, containanaudioprocessingunit or audio processor.

[0013] Throughout this disclosure, including in the claims, the term "couples" or "coupled" is used in a broad sense to mean either a direct or indirect connection. Thus, if a first device couples to a second device, that connection may be through a direct connection, or through an indirect connection via other devices and connections. Moreover, components that are integrated into or with other components are also coupled to each other. Detailed Description of Embodiments of the Invention

[0014] TheMPEG‑4AACstandardcontemplates that anencodedMPEG‑4AACbitstream includesmetadata indicative of each type of high frequency reconstruction ("HFR") processing to be applied (if any is to be applied) by a decoder to decode audio content of the bitstream, and / or which controls such HFR processing, and / or is indicative of at least one characteristic or parameter of at least one HFR tool to be employed to decode audio content of the bitstream. Herein, we use the expression "SBRmetadata" to denotemetadata of this type which is described ormentioned in theMPEG‑4 AAC standard for use with spectral band replication ("SBR"). As appreciated by one skilled in the art, SBR is a form of HFR.

[0015] SBR is preferably used as a dual-rate system, with the underlying codec operating at half the original sampling- rate, while SBR operates at the original sampling rate. The SBR encoder works in parallel with the underlying core codec, albeit at ahigher sampling-rate.AlthoughSBR ismainlyapost process in thedecoder, important parameters areextracted in the encoder in order to ensure the most accurate high frequency reconstruction in the decoder. The encoder estimates the spectral envelope of the SBR range for a time and frequency range / resolution suitable for the current input signal segments characteristics. The spectral envelope is estimated by a complex QMF analysis and subsequent energy calculation. The time and frequency resolutions of the spectral envelopes can be chosen with a high level of freedom, in order to ensure the best suited time frequency resolution for the given input segment. The envelope estimation needs to consider that a transient in theoriginal,mainly situated in thehigh frequency region (for instanceahigh-hat),will bepresent to aminor extent in theSBRgenerated highband prior to envelope adjustment, since the highband in the decoder is based on the low band where the transient is much less pronounced compared to the highband. This aspect imposes different requirements for the time frequency resolution of the spectral envelope data, compared to ordinary spectral envelope estimation as used in other audio coding algorithms. 3 EP 4 756 801 A1 5 10 15 20 25 30 35 40 45 50 55

[0016] Apart from the spectral envelope, several additional parameters are extracted representing spectral character- istics of the input signal for different time and frequency regions. Since the encoder naturally has access to the original signal as well as information on how the SBR unit in the decoder will create the high-band, given the specific set of control parameters, it is possible for the system to handle situations where the lowband constitutes a strong harmonic series and the highband, to be recreated, mainly constitutes random signal components, as well as situations where strong tonal components are present in the original highband without counterparts in the lowband, upon which the highband region is based. Furthermore, the SBR encoder works in close relation to the underlying core codec to assess which frequency range should be covered by SBR at a given time. The SBR data is efficiently coded prior to transmission by exploiting entropy coding as well as channel dependencies of the control data, in the case of stereo signals.

[0017] Thecontrol parameter extractionalgorithms typically need tobecarefully tuned to theunderlyingcodecat agiven bitrate andagiven sampling rate. This is due to the fact that a lowerbitrate, usually implies a largerSBR rangecompared to a high bitrate, and different sampling rates correspond to different time resolutions of the SBR frames.

[0018] An SBR decoder typically includes several different parts. It comprises a bitstream decoding module, a high frequency reconstruction (HFR) module, an additional high frequency components module, and an envelope adjuster module. The system is basedarounda complex valuedQMFfilterbank. In the bitstreamextractionmodule the control data is read from the bitstream and decoded. The time frequency grid is obtained for the current frame, prior to reading the envelope data from the bitstream. The underlying core decoder decodes the audio signal of the current frame (albeit at the lower sampling rate) to produce time-domain audio samples. The resulting frame of audio data is used for high frequency reconstruction by the HFR module. The decoded lowband signal is then analyzed using a QMF filterbank. The high frequency reconstruction and envelope adjustment is subsequently performed on the subband samples of the QMF filterbank. The high frequencies are reconstructed from the lowband in a flexible way, based on the given control parameters. Furthermore, the reconstructed highband is adaptively filtered on a subband channel basis according to the control data to ensure the appropriate spectral characteristics of the given time / frequency region.

[0019] The top level of an MPEG‑4 AAC bitstream is a sequence of data blocks ("raw_data_block" elements), each of which isasegmentofdata (herein referred toasa "block") that containsaudiodata (typically for a timeperiodof1024or960 samples) and related information and / or other data. Herein, we use the term "block" to denote a segment of an MPEG‑4 AAC bitstream comprising audio data (and corresponding metadata and optionally also other related data) which determines or is indicative of one (but not more than one) "raw_data_block" element.

[0020] Each block of an MPEG‑4 AAC bitstream can include a number of syntactic elements (each of which is also materialized in the bitstream as a segment of data). Seven types of such syntactic elements are defined in the MPEG‑4 AAC standard. Each syntactic element is identified by a different value of the data element "id_syn_ele." Examples of syntactic elements include a "single_channel_element()," a "channel_pair_element()," and a "fill_element()." A single channel element is a container including audio data of a single audio channel (amonophonic audio signal). A channel pair element includes audio data of two audio channels (that is, a stereo audio signal).

[0021] A fill element is a container of information including an identifier (e.g., the value of the above-noted element "id_syn_ele") followed by data, which is referred to as "fill data." Fill elements have historically been used to adjust the instantaneous bit rate of bitstreams that are to be transmitted over a constant rate channel. By adding the appropriate amount of fill data to each block, a constant data rate may be achieved.

[0022] In accordance with embodiments on the invention, the fill data may include one or more extension payloads that extend the type of data (e.g., metadata) capable of being transmitted in a bitstream. A decoder that receives bitstreams with fill data containing a new type of data may optionally be used by a device receiving the bitstream (e.g., a decoder) to extend the functionality of thedevice. Thus, ascanbeappreciatedbyoneskilled in theart, fill elementsareaspecial typeof data structure and are different from the data structures typically used to transmit audio data (e.g., audio payloads containing channel data).

[0023] In some embodiments of the invention, the identifier used to identify a fill element may consist of a three bit unsigned integer transmittedmost significant bit first ("uimsbf") havinga valueof 0x6. In oneblock, several instancesof the same type of syntactic element (e.g., several fill elements) may occur.

[0024] Another standard for encoding audio bitstreams is the MPEG Unified Speech and Audio Coding (USAC) standard (ISO / IEC 23003‑3:2012). TheMPEGUSAC standard describes encoding and decoding of audio content using spectral band replication processing (including SBR processing as described in the MPEG‑4 AAC standard, and also includingotherenhanced formsof spectral band replicationprocessing). This processingapplies spectral band replication tools (sometimes referred tohereinas "enhancedSBRtools" or "eSBR tools") of anexpandedandenhancedversionof the set ofSBR tools described in theMPEG‑4AACstandard. Thus, eSBR (asdefined inUSACstandard) is an improvement to SBR (as defined in MPEG‑4 AAC standard).

[0025] Herein, we use the expression "enhanced SBR processing" (or "eSBR processing") to denote spectral band replication processing using at least one eSBR tool (e.g., at least one eSBR tool which is described or mentioned in the MPEGUSACstandard) which is not described ormentioned in theMPEG‑4AAC standard. Examples of such eSBR tools are harmonic transposition and QMF-patching additional pre-processing or "pre-flattening." 4 EP 4 756 801 A1 5 10 15 20 25 30 35 40 45 50 55

[0026] A harmonic transposer of integer order T maps a sinusoid with frequency ω into a sinusoid with frequency Tω, while preserving signal duration. Three orders, T = 2, 3, 4, are typically used in sequence to produce each part of the desired output frequency range using the smallest possible transposition order. If output above the fourth order transposition range is required, it may be generated by frequency shifts.When possible, near critically sampled baseband time domains are created for the processing to minimize computational complexity.

[0027] Abitstream generated in accordancewith theMPEGUSAC standard (sometimes referred to herein as a "USAC bitstream") includes encoded audio content and typically includes metadata indicative of each type of spectral band replication processing to be applied by a decoder to decode audio content of the USAC bitstream, and / ormetadata which controls such spectral band replication processing and / or is indicative of at least one characteristic or parameter of at least one SBR tool and / or eSBR tool to be employed to decode audio content of the USAC bitstream.

[0028] Herein,weuse theexpression "enhancedSBRmetadata" (or "eSBRmetadata") todenotemetadata indicativeof each type of spectral band replication processing to be applied by a decoder to decode audio content of an encoded audio bitstream (e.g., a USACbitstream) and / or which controls such spectral band replication processing, and / or is indicative of at least one characteristic or parameter of at least one SBR tool and / or eSBR tool to be employed to decode such audio content, but which is not described or mentioned in the MPEG‑4 AAC standard. An example of eSBR metadata is the metadata (indicative of, or for controlling, spectral band replication processing) which is described or mentioned in the MPEGUSACstandard but not in theMPEG‑4AACstandard. Thus, eSBRmetadata herein denotesmetadatawhich is not SBR metadata, and SBR metadata herein denotes metadata which is not eSBR metadata.

[0029] A USAC bitstream may include both SBR metadata and eSBR metadata. More specifically, a USAC bitstream may include eSBRmetadatawhich controls the performance of eSBRprocessing by a decoder, andSBRmetadatawhich controls the performance of SBR processing by the decoder. In accordance with typical embodiments of the present invention, eSBRmetadata (e.g., eSBR-specific configuration data) is included (in accordance with the present invention) in an MPEG‑4 AAC bitstream (e.g., in the sbr_extension() container at the end of an SBR payload).

[0030] Performance of eSBRprocessing, during decoding of an encoded bitstream using an eSBR tool set (comprising at least one eSBR tool), by a decoder regenerates the high frequency band of the audio signal, based on replication of sequences of harmonics which were truncated during encoding. Such eSBR processing typically adjusts the spectral envelopeof thegeneratedhigh frequencybandandapplies inversefiltering, andaddsnoiseandsinusoidal components in order to recreate the spectral characteristics of the original audio signal.

[0031] In accordance with typical embodiments of the invention, eSBR metadata is included (e.g., a small number of control bits which are eSBRmetadata are included) in one or more of metadata segments of an encoded audio bitstream (e.g., an MPEG‑4 AAC bitstream) which also includes encoded audio data in other segments (audio data segments). Typically, at least one such metadata segment of each block of the bitstream is (or includes) a fill element (including an identifier indicating the start of the fill element), and the eSBR metadata is included in the fill element after the identifier.

[0032] FIG. 1 is a block diagram of an exemplary audio processing chain (an audio data processing system), in which one ormore of the elements of the systemmay be configured in accordancewith an embodiment of the present invention. The system includes the following elements, coupled together as shown: encoder 1, delivery subsystem2, decoder 3, and post-processingunit 4. In variationson thesystemshown,oneormoreof theelementsareomitted,or additional audiodata processing units are included.

[0033] In some implementations, encoder 1 (which optionally includes a pre-processing unit) is configured to accept PCM (time-domain) samples comprising audio content as input, and to output an encoded audio bitstream (having format which is compliant with theMPEG‑4 AAC standard) which is indicative of the audio content. The data of the bitstream that are indicative of the audio content are sometimes referred to herein as "audio data" or "encodedaudio data." If the encoder is configured in accordance with a typical embodiment of the present invention, the audio bitstream output from the encoder includes eSBR metadata (and typically also other metadata) as well as audio data.

[0034] One or more encoded audio bitstreams output from encoder 1 may be asserted to encoded audio delivery subsystem 2. Subsystem 2 is configured to store and / or deliver each encoded bitstream output from encoder 1. An encodedaudiobitstreamoutput fromencoder1maybestoredbysubsystem2 (e.g., in the formofaDVDorBlu raydisc), or transmitted by subsystem 2 (whichmay implement a transmission link or network), or may be both stored and transmitted by subsystem 2.

[0035] Decoder 3 is configured to decode an encodedMPEG‑4 AAC audio bitstream (generated by encoder 1) which it receives via subsystem2. In someembodiments, decoder 3 is configured toextract eSBRmetadata fromeachblockof the bitstream, and to decode the bitstream (including by performing eSBRprocessing using the extracted eSBRmetadata) to generate decoded audio data (e.g., streams of decoded PCM audio samples). In some embodiments, decoder 3 is configured to extract SBR metadata from the bitstream (but to ignore eSBR metadata included in the bitstream), and to decode the bitstream (including by performing SBR processing using the extracted SBRmetadata) to generate decoded audio data (e.g., streams of decoded PCM audio samples).Typically, decoder 3 includes a buffer which stores (e.g., in a non-transitory manner) segments of the encoded audio bitstream received from subsystem 2.

[0036] Post-processing unit 4 of Fig. 1 is configured to accept a stream of decoded audio data from decoder 3 (e.g., 5 EP 4 756 801 A1 5 10 15 20 25 30 35 40 45 50 55 decoded PCM audio samples), and to perform post processing thereon. Post-processing unit may also be configured to render the post-processed audio content (or the decoded audio received from decoder 3) for playback by one or more speakers.

[0037] FIG. 2 is a block diagramof an encoder (100)which is an embodiment of the inventive audio processing unit. Any of the components or elements of encoder 100maybe implementedas oneormore processes and / or one ormore circuits (e.g., ASICs, FPGAs, or other integrated circuits), in hardware, software, or a combination of hardware and software. Encoder 100 includes encoder 105, stuffer / formatter stage 107, metadata generation stage 106, and buffer memory 109, connected as shown. Typically also, encoder 100 includes other processing elements (not shown). Encoder 100 is configured to convert an input audio bitstream to an encoded output MPEG‑4 AAC bitstream.

[0038] Metadata generator 106 is coupled and configured to generate (and / or pass through to stage 107) metadata (including eSBR metadata and SBR metadata) to be included by stage 107 in the encoded bitstream to be output from encoder 100.

[0039] Encoder 105 is coupled and configured to encode (e.g., by performing compression thereon) the input audio data, and to assert the resulting encoded audio to stage 107 for inclusion in the encoded bitstream to be output from stage 107.

[0040] Stage 107 is configured to multiplex the encoded audio from encoder 105 and the metadata (including eSBR metadata and SBR metadata) from generator 106 to generate the encoded bitstream to be output from stage 107, preferably so that the encoded bitstream has format as specified by one of the embodiments of the present invention.

[0041] Buffermemory109 isconfigured tostore (e.g., inanon-transitorymanner) at leastoneblockof theencodedaudio bitstreamoutput from stage 107, and a sequence of the blocks of the encoded audio bitstream is then asserted frombuffer memory 109 as output from encoder 100 to a delivery system.

[0042] FIG. 3 is a block diagram of a system including decoder (200) which is an embodiment of the inventive audio processing unit, and optionally also a post-processor (300) coupled thereto. Any of the components or elements of decoder 200 and post-processor 300 may be implemented as one or more processes and / or one or more circuits (e.g., ASICs, FPGAs, or other integrated circuits), in hardware, software, or a combination of hardware and software. Decoder 200 comprises buffer memory 201, bitstream payload deformatter (parser) 205, audio decoding subsystem 202 (some- times referred to as a "core" decoding stage or "core" decoding subsystem), eSBR processing stage 203, and control bit generation stage 204, connected as shown. Typically also, decoder 200 includes other processing elements (not shown).

[0043] Buffer memory (buffer) 201 stores (e.g., in a non-transitory manner) at least one block of an encoded MPEG‑4 AAC audio bitstream received by decoder 200. In operation of decoder 200, a sequence of the blocks of the bitstream is asserted from buffer 201 to deformatter 205.

[0044] In variations on theFig. 3 embodiment (or theFig. 4 embodiment to bedescribed), anAPUwhich is not a decoder (e.g., APU 500 of FIG. 6) includes a buffer memory (e.g., a buffer memory identical to buffer 201) which stores (e.g., in a non-transitory manner) at least one block of an encoded audio bitstream (e.g., an MPEG‑4 AAC audio bitstream) of the same type received by buffer 201 of Fig. 3 or Fig. 4 (i.e., an encoded audio bitstream which includes eSBR metadata).

[0045] With reference again to Fig. 3, deformatter 205 is coupled and configured to demultiplex each block of the bitstream to extract SBR metadata (including quantized envelope data) and eSBR metadata (and typically also other metadata) therefrom, to assert at least the eSBR metadata and the SBR metadata to eSBR processing stage 203, and typically also to assert other extracted metadata to decoding subsystem 202 (and optionally also to control bit generator 204). Deformatter 205 is also coupled and configured to extract audio data from each block of the bitstream, and to assert the extracted audio data to decoding subsystem (decoding stage) 202.

[0046] The system of FIG. 3 optionally also includes post-processor 300. Post-processor 300 includes buffer memory (buffer) 301 and other processing elements (not shown) including at least one processing element coupled to buffer 301. Buffer 301 stores (e.g., in a non-transitory manner) at least one block (or frame) of the decoded audio data received by post-processor 300 fromdecoder 200. Processing elements of post-processor 300 are coupled and configured to receive and adaptively process a sequence of the blocks (or frames) of the decoded audio output from buffer 301, usingmetadata output from decoding subsystem 202 (and / or deformatter 205) and / or control bits output from stage 204 of decoder 200.

[0047] Audio decoding subsystem 202 of decoder 200 is configured to decode the audio data extracted by parser 205 (such decoding may be referred to as a "core" decoding operation) to generate decoded audio data, and to assert the decoded audio data to eSBR processing stage 203. The decoding is performed in the frequency domain and typically includes inverse quantization followed by spectral processing. Typically, a final stage of processing in subsystem 202 applies a frequency domain-to-time domain transform to the decoded frequency domain audio data, so that the output of subsystem is time domain, decoded audio data. Stage 203 is configured to apply SBR tools and eSBR tools indicated by the eSBR metadata and the eSBR (extracted by parser 205) to the decoded audio data (i.e., to perform SBR and eSBR processing on the output of decoding subsystem 202 using the SBR and eSBR metadata) to generate the fully decoded audio data which is output (e.g., to post-processor 300) from decoder 200. Typically, decoder 200 includes a memory (accessible by subsystem 202 and stage 203) which stores the deformatted audio data and metadata output from deformatter 205, and stage 203 is configured to access the audio data andmetadata (including SBRmetadata and eSBR 6 EP 4 756 801 A1 5 10 15 20 25 30 35 40 45 50 55 metadata) as needed during SBRand eSBRprocessing. TheSBRprocessing and eSBRprocessing in stage 203may be considered to be post-processing on the output of core decoding subsystem 202. Optionally, decoder 200 also includes a final upmixing subsystem (whichmayapply parametric stereo ("PS") tools defined in theMPEG‑4AACstandard, usingPS metadataextractedbydeformatter205and / or control bits generated insubsystem204)which is coupledandconfigured to performupmixing on the output of stage 203 to generated fully decoded, upmixed audiowhich is output fromdecoder 200. Alternatively, post-processor 300 is configured to performupmixing on theoutput of decoder 200 (e.g., usingPSmetadata extracted by deformatter 205 and / or control bits generated in subsystem 204).

[0048] In response tometadata extracted by deformatter 205, control bit generator 204may generate control data, and the control datamaybeusedwithin decoder 200 (e.g., in a final upmixingsubsystem) and / or assertedasoutput of decoder 200 (e.g., to post-processor 300 for use in post-processing). In response to metadata extracted from the input bitstream (and optionally also in response to control data), stage 204 may generate (and assert to post-processor 300) control bits indicating that decoded audio data output from eSBR processing stage 203 should undergo a specific type of post- processing. In some implementations, decoder200 is configured toassertmetadataextractedbydeformatter205 from the input bitstream to post-processor 300, and post-processor 300 is configured to perform post-processing on the decoded audio data output from decoder 200 using the metadata.

[0049] FIG. 4 is a block diagramof an audio processing unit ("APU") (210) which is another embodiment of the inventive audio processing unit. APU 210 is a legacy decoder which is not configured to perform eSBR processing. Any of the components or elements of APU 210 may be implemented as one or more processes and / or one or more circuits (e.g., ASICs, FPGAs, or other integrated circuits), in hardware, software, or a combination of hardware and software. APU 210 comprises buffer memory 201, bitstream payload deformatter (parser) 215, audio decoding subsystem 202 (sometimes referred to as a "core" decoding stage or "core" decoding subsystem), and SBR processing stage 213, connected as shown.Typically also,APU210 includesother processing elements (not shown).APU210may represent, for example, an audio encoder, decoder or transcoder.

[0050] Elements 201 and 202 of APU 210 are identical to the identically numbered elements of decoder 200 (of Fig. 3) and the abovedescription of themwill not be repeated. In operation of APU210, a sequenceof blocks of anencodedaudio bitstream (an MPEG‑4 AAC bitstream) received by APU 210 is asserted from buffer 201 to deformatter 215.

[0051] Deformatter 215 is coupled and configured to demultiplex each block of the bitstream to extract SBR metadata (includingquantizedenvelopedata) and typically alsoothermetadata therefrom,but to ignoreeSBRmetadata thatmaybe included in the bitstream in accordance with any embodiment of the present invention. Deformatter 215 is configured to assert at least the SBRmetadata to SBRprocessing stage 213. Deformatter 215 is also coupled and configured to extract audio data from each block of the bitstream, and to assert the extracted audio data to decoding subsystem (decoding stage) 202.

[0052] Audio decoding subsystem 202 of decoder 200 is configured to decode the audio data extracted by deformatter 215 (such decodingmay be referred to as a "core" decoding operation) to generate decoded audio data, and to assert the decoded audio data to SBR processing stage 213. The decoding is performed in the frequency domain. Typically, a final stage of processing in subsystem 202 applies a frequency domain-to-time domain transform to the decoded frequency domain audio data, so that the output of subsystem is time domain, decoded audio data. Stage 213 is configured to apply SBR tools (but not eSBR tools) indicated by the SBRmetadata (extracted by deformatter 215) to the decoded audio data (i.e., to perform SBR processing on the output of decoding subsystem 202 using the SBRmetadata) to generate the fully decoded audio data which is output (e.g., to post-processor 300) from APU 210. Typically, APU 210 includes a memory (accessible by subsystem 202 and stage 213) which stores the deformatted audio data and metadata output from deformatter 215, and stage213 is configured to access the audio data andmetadata (includingSBRmetadata) as needed during SBR processing. The SBR processing in stage 213may be considered to be post-processing on the output of core decoding subsystem 202. Optionally, APU 210 also includes a final upmixing subsystem (which may apply parametric stereo ("PS") tools defined in the MPEG‑4 AAC standard, using PS metadata extracted by deformatter 215) which is coupledandconfigured toperformupmixingon theoutput of stage213 togenerated fully decoded, upmixedaudiowhich is output from APU 210. Alternatively, a post-processor is configured to perform upmixing on the output of APU 210 (e.g., using PS metadata extracted by deformatter 215 and / or control bits generated in APU 210).

[0053] Various implementations of encoder 100, decoder 200, and APU 210 are configured to perform different embodiments of the inventive method.

[0054] In accordance with some embodiments, eSBR metadata is included (e.g., a small number of control bits which are eSBR metadata are included) in an encoded audio bitstream (e.g., an MPEG‑4 AAC bitstream), such that legacy decoders (which are not configured to parse the eSBR metadata, or to use any eSBR tool to which the eSBR metadata pertains) can ignore the eSBR metadata but nevertheless decode the bitstream to the extent possible without use of the eSBR metadata or any eSBR tool to which the eSBR metadata pertains, typically without any significant penalty in decoded audio quality. However, eSBR decoders configured to parse the bitstream to identify the eSBRmetadata and to use at least one eSBR tool in response to the eSBRmetadata, will enjoy the benefits of using at least one such eSBR tool. Therefore, embodiments of the invention provide a means for efficiently transmitting enhanced spectral band replication 7 EP 4 756 801 A1 5 10 15 20 25 30 35 40 45 50 55 (eSBR) control data or metadata in a backward-compatible fashion.

[0055] Typically, the eSBR metadata in the bitstream is indicative of (e.g., is indicative of at least one characteristic or parameter of) one ormore of the following eSBR tools (which are described in theMPEGUSAC standard, and whichmay or may not have been applied by an encoder during generation of the bitstream): • Harmonic transposition; and • QMF-patching additional pre-processing (pre-flattening).

[0056] For example, the eSBR metadata included in the bitstream may be indicative of values of the parameters (described in theMPEGUSACstandard and in the present disclosure): sbrPatchingMode[ch], sbrOversamplingFlag[ch], sbrPitchInBins[ch], sbrPitchInBins[ch], and bs_sbr_preprocessing.

[0057] Herein, the notation X[ch], where X is some parameter, denotes that the parameter pertains to channel ("ch") of audio content of an encoded bitstream to be decoded. For simplicity, we sometimes omit the expression [ch], and assume the relevant parameter pertains to a channel of audio content.

[0058] Herein, the notation X[ch][env], where X is some parameter, denotes that the parameter pertains to SBR envelope ("env") of channel ("ch") of audio content of an encoded bitstream to be decoded. For simplicity, we sometimes omit the expressions [env] and [ch], andassume the relevant parameter pertains to anSBRenvelopeof a channel of audio content.

[0059] During decoding of an encoded bitstream, performance of harmonic transposition during an eSBR processing stage of the decoding (for each channel, "ch", of audio content indicated by the bitstream) is controlled by the following eSBR metadata parameters: sbrPatchingMode[ch]: sbrOversamplingFlag[ch]; sbrPitchInBinsFlag[ch]; and sbrPitchIn- Bins[ch].

[0060] The value "sbrPatchingMode[ch]" indicates the transposer type used in eSBR: sbrPatchingMode[ch] = 1 indicates non-harmonic patching as described in Section 4.6.18.6.3 of the MPEG‑4 AAC standard; sbrPatchingMode [ch] = 0 indicates harmonic SBR patching as described in Section 7.5.3 or 7.5.4 of the MPEG USAC standard.

[0061] The value "sbrOversamplingFlag[ch]" indicates the use of signal adaptive frequency domain oversampling in eSBR in combination with the DFT based harmonic SBR patching as described in Section 7.5.3 of the MPEG USAC standard. This flag controls the size of the DFTs that are utilized in the transposer: 1 indicates signal adaptive frequency domain oversampling enabled as described in Section 7.5.3.1 of the MPEG USAC standard; 0 indicates signal adaptive frequency domain oversampling disabled as described in Section 7.5.3.1 of the MPEG USAC standard.

[0062] The value "sbrPitchinBinsFlag[ch]" controls the interpretation of the sbrPitchInBins[ch] parameter: 1 indicates that the value in sbrPitchinBins[ch] is valid and greater than zero; 0 indicates that the value of sbrPitchInBins[ch] is set to zero.

[0063] The value "sbrPitchinBins[ch]" controls the addition of cross product terms in the SBR harmonic transposer. The value sbrPitchinBins[ch] is an integer value in the range [0,127] and represents the distance measured in frequency bins for a 1536-line DFT acting on the sampling frequency of the core coder.

[0064] In the case that anMPEG‑4 AAC bitstream is indicative of an SBR channel pair whose channels are not coupled (rather than a single SBR channel), the bitstream is indicative of two instances of the above syntax (for harmonic or non- harmonic transposition), one for each channel of the sbr_channel_pair_element().

[0065] The harmonic transposition of the eSBR tool typically improves the quality of decoded musical signals at relatively low cross over frequencies. Non-harmonic transposition (that is, legacy spectral patching) typically improves speech signals. Hence, a starting point in the decision as to which type of transposition is preferable for encoding specific audio content is to select the transposition method depending on speech / music detection with harmonic transposition be employed on the musical content and spectral patching on the speed content.

[0066] Performance of pre-flattening during eSBR processing is controlled by the value of a one-bit eSBR metadata parameter known as "bs_sbr_preprocessing", in the sense that pre-flattening is either performed or not performed depending on the value of this single bit.When theSBRQMF-patching algorithm, as described inSection 4.6.18.6.3 of the MPEG‑4 AAC standard, is used, the step of pre-flattening may be performed (when indicated by the "bs_sbr_preproces- sing" parameter) in an effort to avoid discontinuities in the shape of the spectral envelope of a high frequency signal being input to a subsequent envelopeadjuster (the envelopeadjuster performsanother stageof the eSBRprocessing). Thepre- flattening typically improves the operation of the subsequent envelope adjustment stage, resulting in a highband signal that is perceived to be more stable.

[0067] The overall bitrate requirement for including in an MPEG‑4 AAC bitstream eSBR metadata indicative of the above-mentioned eSBR tools (harmonic transposition and pre-flattening) is expected to be on the order of a fewhundreds of bits per second because only the differential control data needed to perform eSBR processing is transmitted in accordance with some embodiments of the invention. Legacy decoders can ignore this information because it is included in abackward compatiblemanner (aswill beexplained later). Therefore, thedetrimental effect onbitrateassociatedwith of 8 EP 4 756 801 A1 5 10 15 20 25 30 35 40 45 50 55 inclusion of eSBR metadata is negligible, for a number of reasons, including the following: • The bitrate penalty (due to including the eSBRmetadata) is a very small fraction of the total bitrate because only the differential control data needed to perform eSBR processing is transmitted (and not a simulcast of the SBR control data); and • The tuning of SBR related control information does typically not depend of the details of the transposition.

[0068] Thus, embodiments of the invention provide a means for efficiently transmitting enhanced spectral band replication (eSBR) control data or metadata in a backward-compatible fashion. This efficient transmission of the eSBR control data reduces memory requirements in decoders, encoders, and transcoders employing aspects of the invention, while having no tangible adverse effect on bitrate.Moreover, the complexity and processing requirements associatedwith performing eSBR in accordance with embodiments of the invention are also reduced because the SBR data needs to be processedonly onceandnot simulcast, whichwould be the case if eSBRwas treated asa completely separate object type in MPEG‑4 AAC instead of being integrated into the MPEG‑4 AAC codec in a backward-compatible manner.

[0069] Next, with reference to FIG. 7, we describe elements of a block ("raw_data_block") of anMPEG‑4AACbitstream inwhich eSBRmetadata is included in accordancewith someembodiments of thepresent invention. FIG. 7 is adiagramof a block (a "raw_data_block") of the MPEG‑4 AAC bitstream, showing some of the segments thereof.

[0070] A block of an MPEG‑4 AAC bitstream may include at least one "single_channel_element()" (e.g., the single channel element shown inFig. 7), and / or at least one "channel_pair_element()" (not specifically shown in Fig. 7 although it may be present), including audio data for an audio program. The blockmay also include a number of "fill_elements" (e.g., fill element 1 and / or fill element 2 of Fig. 7) including data (e.g., metadata) related to the program. Each "single_channe- l_element()" includes an identifier (e.g., "ID1" of Fig. 7) indicating the start of a single channel element, and can include audio data indicative of a different channel of a multi-channel audio program. Each "channel_pair_element includes an identifier (not shown in Fig. 7) indicating the start of a channel pair element, and can include audio data indicative of two channels of the program.

[0071] Afill_element (referred tohereinasafill element) of anMPEG‑4AACbitstream includesan identifier ("ID2"ofFig. 7) indicating the start of a fill element, and fill data after the identifier. The identifier ID2may consist of a three bit unsigned integer transmitted most significant bit first ("uimsbf") having a value of 0x6. The fill data can include an extension_pay- load() element (sometimes referred tohereinasanextensionpayload)whosesyntax is shown inTable4.57of theMPEG‑4 AACstandard.Several typesofextensionpayloadsexist andare identified through the "extension_type"parameter,which is a four bit unsigned integer transmitted most significant bit first ("uimsbf").

[0072] Thefill data (e.g., an extensionpayload thereof) can includeaheader or identifier (e.g., "header1" of Fig. 7)which indicatesasegmentof fill datawhich is indicativeofanSBRobject (i.e., theheader initializesan "SBRobject" type, referred to as sbr_extension_data() in the MPEG‑4 AAC standard). For example, a spectral band replication (SBR) extension payload is identified with the value of ’1101’ or ’1110’ for the extension_type field in the header, with the identifier ’1101’ identifying an extension payload with SBR data and ’1110’ identifying and extension payload with SBR data with a Cyclic Redundancy Check (CRC) to verify the correctness of the SBR data.

[0073] When the header (e.g., the extension_type field) initializes an SBR object type, SBR metadata (sometimes referred to herein as "spectral band replication data," and referred to as sbr_data() in theMPEG‑4 AAC standard) follows theheader, andat least onespectral band replicationextensionelement (e.g., the "SBRextensionelement" of fill element1 of Fig. 7) can follow theSBRmetadata. Such a spectral band replication extension element (a segment of the bitstream) is referred to as an "sbr_extension()" container in theMPEG‑4AACstandard. A spectral band replication extension element optionally includes a header (e.g., "SBR extension header" of fill element 1 of Fig. 7).

[0074] The MPEG‑4 AAC standard contemplates that a spectral band replication extension element can include PS (parametric stereo) data for audio data of a program. TheMPEG‑4 AAC standard contemplates that when the header of a fill element (e.g., of anextensionpayload thereof) initializesanSBRobject type (asdoes "header1" ofFig. 7) andaspectral band replicationextensionelementof thefill element includesPSdata, thefill element (e.g., theextensionpayload thereof) includes spectral band replication data, and a "bs_extension_id" parameter whose value (i.e., bs_extension_id = 2) indicates that PS data is included in a spectral band replication extension element of the fill element.

[0075] In accordance with some embodiments of the present invention, eSBR metadata (e.g., a flag indicative of whether enhanced spectral band replication (eSBR) processing is to be performed on audio content of the block) is included in a spectral band replication extension element of a fill element. For example, such a flag is indicated in fill element 1 of Fig. 7, where the flag occurs after the header (the "SBRextension header" of fill element 1) of "SBRextension element" of fill element 1. Optionally, such a flag and additional eSBRmetadata are included in a spectral band replication extension element after the spectral band replication extensionelement’s header (e.g., in theSBRextensionelement of fill element 1 in Fig. 7, after the SBRextension header). In accordancewith some embodiments of the present invention, a fill elementwhich includes eSBRmetadata also includes a "bs_extension_id" parameterwhose value (e.g., bs_extension_id 9 EP 4 756 801 A1 5 10 15 20 25 30 35 40 45 50 55 = 3) indicates that eSBR metadata is included in the fill element and that eSBR processing is to be performed on audio content of the relevant block.

[0076] In accordance with some embodiments of the invention, eSBR metadata is included in a fill element (e.g., fill element 2 of Fig. 7) of an MPEG‑4 AAC bitstream other than in a spectral band replication extension element (SBR extension element) of the fill element. This is because fill elements containing an extension_payload() with SBR data or SBR data with a CRCdo not contain any other extension payload of any other extension type. Therefore, in embodiments where eSBR metadata is stored its own extension payload, a separate fill element is used to store the eSBR metadata. Such a fill element includes an identifier (e.g., "ID2" of Fig. 7) indicating the start of a fill element, and fill data after the identifier. Thefill datacan includeanextension_payload() element (sometimes referred tohereinasanextensionpayload) whose syntax is shown in Table 4.57 of the MPEG‑4 AAC standard. The fill data (e.g., an extension payload thereof) includes aheader (e.g., "header2" of fill element 2of Fig. 7)which is indicative of aneSBRobject (i.e., the header initializes an enhanced spectral band replication (eSBR) object type), and the fill data (e.g., an extension payload thereof) includes eSBRmetadataafter theheader.Forexample, fill element2ofFig. 7 includessuchaheader ("header2")andalso includes, after the header, eSBR metadata (i.e., the "flag" in fill element 2, which is indicative of whether enhanced spectral band replication (eSBR) processing is to be performed on audio content of the block). Optionally, additional eSBRmetadata is also included in the fill data of fill element 2 of Fig. 7, after header2. In the embodiments being described in the present paragraph, the header (e.g., header2 of Fig. 7) has an identification value which is not one of the conventional values specified in Table 4.57 of the MPEG‑4 AAC standard, and is instead indicative of an eSBR extension payload (so that the header’s extension_type field indicates that the fill data includes eSBR metadata).

[0077] In a first class of embodiments, the invention is an audio processing unit (e.g., a decoder), comprising: amemory (e.g., buffer 201 of Fig. 3 or 4) configured to store at least one block of an encoded audio bitstream (e.g., at least one block of an MPEG‑4 AAC bitstream); a bitstream payload deformatter (e.g., element 205 of Fig. 3 or element 215 of Fig. 4) coupled to the memory and configured to demultiplex at least one portion of said block of the bitstream; and a decoding subsystem (e.g., elements 202 and 203 of Fig. 3, or elements 202 and 213 of Fig. 4), coupled and configured to decode at least one portion of audio content of said block of the bitstream, wherein the block includes: a fill element, including an identifier indicating a start of the fill element (e.g., the "id_syn_ele" identifier having value 0x6, of Table 4.85 of the MPEG‑4 AAC standard), and fill data after the identifier, wherein the fill data includes: at least one flag identifying whether enhanced spectral band replication (eSBR) processing is to be performed on audio content of the block (e.g., using spectral band replication data and eSBR metadata included in the block).

[0078] Theflag iseSBRmetadata,andanexampleof theflag is thesbrPatchingModeflag.Anotherexampleof theflag is theharmonicSBRflag.Bothof theseflags indicatewhether abase formof spectral band replicationor anenhanced formof spectral replication is to be performed on the audio data of the block. The base form of spectral replication is spectral patching, and the enhanced form of spectral band replication is harmonic transposition.

[0079] In some embodiments, the fill data also includes additional eSBRmetadata (i.e., eSBRmetadata other than the flag).

[0080] Thememorymaybea buffermemory (e.g., an implementation of buffer 201 of Fig. 4)which stores (e.g., in a non- transitory manner) the at least one block of the encoded audio bitstream.

[0081] It is estimated that the complexity of performance of eSBR processing (using the eSBR harmonic transposition and pre-flattening) by an eSBR decoder during decoding of an MPEG‑4 AAC bitstream which includes eSBR metadata (indicative of these eSBR tools) would be as follows (for typical decoding with the indicated parameters): • Harmonic transposition (16 kbps, 14400 / 28800 Hz) ∘ DFT based: 3.68 WMOPS (weighted million operations per second); ∘ QMF based: 0.98 WMOPS; • QMF-patching pre-processing (pre-flattening): 0.1WMOPS. It is known that DFT based transposition typically performs better than the QMF based transposition for transients.

[0082] In accordance with some embodiments of the present invention, a fill element (of an encoded audio bitstream) which includes eSBR metadata also includes a parameter (e.g., a "bs_extension_id" parameter) whose value (e.g., bs_extension_id = 3) signals that eSBR metadata is included in the fill element and that eSBR processing is to be performed on audio content of the relevant block, and / or or a parameter (e.g., the same "bs_extension_id" parameter) whose value (e.g., bs_extension_id = 2) signals that an sbr_extension() container of the fill element includes PS data. For example, as indicated in Table 1 below, such a parameter having the value bs_extension_id = 2 may signal that an 10 EP 4 756 801 A1 5 10 15 20 25 30 35 40 45 50 55 sbr_extension() container of the fill element includesPSdata, and such a parameter having the value bs_extension_id = 3 may signal that an sbr_extension() container of the fill element includes eSBR metadata: Table 1 bs_extension_id Meaning 0 Reserved 1 Reserved 2 EXTENSION_ID_PS 3 EXTENSION_ID_ESBR

[0083] In accordance with some embodiments of the invention, the syntax of each spectral band replication extension element which includes eSBR metadata and / or PS data is as indicated in Table 2 below (in which "sbr_extension()" denotes a containerwhich is the spectral band replication extension element, "bs_extension_id" is as described in Table 1 above, "ps_data" denotes PS data, and "esbr_data" denotes eSBR metadata) : Table 2 sbr_extension(bs_extension_id, num_bits_left) { switch (bs_extension_id) { case EXTENSION_ID_PS: num_bits_left -= ps_data(); Note 1 break; case EXTENSION_ID_ESBR: num_bits_left -= esbr_data(); Note 2 break; default: bs_fill_bits; num_bits_left = 0; break; } } Note 1: ps_data() returns the number of bits read. Note 2: esbr_data() returns the number of bits read. In an exemplary embodiment, the esbr_data() referred to in Table 2 above is indicative of values of the following meta- data parameters: 1. the one-bit metadata parameter, "bs_sbr_preprocessing"; and 2. for each channel ("ch") of audio content of the encoded bitstream to be decoded, each of the above-described parameters: "sbrPatchingMode[ch]"; "sbrOversamplingFlag[ch]"; "sbrPitchInBinsFlag[ch]"; and "sbrPitchinBins[ch]".

[0084] For example, in some embodiments, the esbr_data() may have the syntax indicated in Table 3, to indicate these metadata parameters: Table 3 Syntax No. of bits esbr_data(id_aac, bs_coupling) 11 EP 4 756 801 A1 5 10 15 20 25 30 35 40 45 50 55 (continued) Syntax No. of bits { bs_sbr_preprocessing ; 1 if (id_aac == ID_SCE) { if (sbrPatchingMode[0] == 0) { 1 sbrOversamplingFlag[0]; 1 if (sbrPitchinBinsFlag[0]) 1 sbrPitchinBins[0]; 7 else sbrPitchInBins[0] = 0; } else { sbrOversamplingFlag[0] = 0; sbrPitchInBins[0] = 0; } } else if (id_aac == ID_CPE) { If (bs_coupling) { if (sbrPatchingMode[0,1] == 0) { 1 sbrOversamplingFlag[0,1]; 1 if (sbrPitchinBinsFlag[0,1]) 1 sbrPitchinBins[0,1]; 7 else sbrPitchInBins[0,1] = 0; } else { sbrOversamplingFlag[0,1] = 0; sbrPitchInBins[0,1] = 0; } } else { / * bs_coupling == 0 * / if (sbrPatchingMode[0] == 0) { 1 sbrOversamplingFlag[0]; 1 if (sbrPitchinBinsFlag[0]) 1 sbrPitchinBins[0]; 7 else sbrPitchinBins[0] = 0; } else { sbrOversamplingFlag[0] = 0; sbrPitchInBins[0] = 0; } if (sbrPatchingMode[1] == 0) { 1 sbrOversamplingFlag[1]; 1 if (sbrPitchinBinsFlag[1]) 1 12 EP 4 756 801 A1 5 10 15 20 25 30 35 40 45 50 55 (continued) Syntax No. of bits sbrPitchinBins[1]; 7 else sbrPitchinBins[1] = 0; } else { sbrOversamplingFlag[1] = 0; sbrPitchInBins[1] = 0; } } } } Note: bs_sbr_preprocessing is defined as described in section 6.2.12 of ISO / IEC 23003‑3:2012. sbrPatchingMode [ch], sbrOversamplingFlag[ch], sbrPitchInBinsFlag[ch] and sbrPitchInBins[ch] are defined as described in section 7.5 of ISO / IEC 23003‑3:2012.

[0085] The above syntax enables an efficient implementation of an enhanced form of spectral band replication, such as harmonic transposition, as an extension to a legacy decoder. Specifically, the eSBR data of Table 3 includes only those parameters needed to perform the enhanced form of spectral band replication that are not either already supported in the bitstream or directly derivable from parameters already supported in the bitstream. All other parameters and processing data needed to perform the enhanced form of spectral band replication are extracted from pre-existing parameters in already-defined locations in the bitstream.

[0086] For example, an MPEG‑4 HE-AAC or HE-AAC v2 compliant decoder may be extended to include an enhanced form of spectral band replication, such as harmonic transposition. This enhanced form of spectral band replication is in addition to the base form of spectral band replication already supported by the decoder. In the context of anMPEG‑4 HE- AACorHE-AACv2compliant decoder, thisbase formof spectral band replication is theQMFspectral patchingSBRtool as defined in Section 4.6.18 of the MPEG‑4 AAC Standard.

[0087] When performing the enhanced form of spectral band replication, an extended HE-AAC decoder may reuse manyof thebitstreamparametersalready included in theSBRextensionpayloadof thebitstream.Thespecificparameters that may be reused include, for example, the various parameters that determine the master frequency band table. These parameters include bs_start_freq (parameter that determines the start of master frequency table parameter), bs_stop_freq (parameter that determines the stop of master frequency table), bs_freq_scale (parameter that determines the number of frequency bands per octave), and bs_alter_scale (parameter that alters the scale of the frequency bands). The parameters that may be reused also include parameters that determine the noise band table (bs_noise_bands) and the limiter band tableparameters (bs_limiter_bands).Accordingly, in variousembodiments, at least someof theequivalent parameters specified in the USAC standard are omitted from the bitstream, thereby reducing control overhead in the bitstream. Typically, where a parameter specified in theAACstandard has an equivalent parameter specified in theUSAC standard, the equivalent parameter specified in the USAC standard has the same name as the parameter specified in the AAC standard, e.g. the envelope scalefactor EOrigMapped. However, the equivalent parameter specified in the USAC standard typically has a different value, which is "tuned" for the enhanced SBR processing defined in the USAC standard rather than for the SBR processing defined in the AAC standard.

[0088] In addition to the numerous parameters, other data elements may also be reused by an extended HE-AAC decoderwhenperforminganenhanced formof spectral band replication inaccordancewithembodimentsof the invention. For example, the envelope data and noise floor datamay also be extracted from the bs_data_env (envelope scalefactors) and bs_noise_env (noise floor scalefactors) data and used during the enhanced form of spectral band replication.

[0089] In essence, these embodiments exploit the configuration parameters and envelope data already supported by a legacy HE-AAC or HE-AAC v2 decoder in the SBR extension payload to enable an enhanced form of spectral band replication requiring as little extra transmitted data as possible. Themetadata was originally tuned for a base form of HFR (e.g., the spectral patching of SBR), but in accordance with embodiments, is used for an enhanced form of HFR (e.g., the harmonic transpositionof eSBR).Aspreviouslydiscussed, themetadatagenerally representsoperatingparameters (e.g., envelope scalefactors, noise floor scalefactors, time / frequency grid parameters, sinusoid addition information, variable cross over frequency / band, inverse filtering mode, envelope resolution, smoothing mode, frequency interpolation mode) 13 EP 4 756 801 A1 5 10 15 20 25 30 35 40 45 50 55 tuned and intended to be usedwith the base form of HFR (e.g., linear translation). However, thismetadata, combinedwith additional metadata parameters specific to the enhanced form of HFR (e.g., harmonic transposition), may be used to efficiently and effectively process the audio data using the enhanced form of HFR.

[0090] Accordingly, extended decoders that support an enhanced form of spectral band replicationmay be created in a very efficientmanner by relying on already defined bitstreamelements (for example, those in the SBRextension payload) and adding only those parameters needed to support the enhanced form of spectral band replication (in a fill element extensionpayload). This data reduction feature combinedwith theplacement of thenewlyaddedparameters ina reserved data field, such as an extension container, substantially reduces the barriers to creating a decoder that supports an enhanced for of spectral band replication by ensuring that the bitstream is backwards-compatible with legacy decoder not supporting the enhanced form of spectral band replication.

[0091] In Table 3, the number in the right column indicates the number of bits of the corresponding parameter in the left column.

[0092] In some embodiments, the SBR object type defined in MPEG‑4 AAC is updated to contain the SBR-Tool or aspects of the enhanced SBR (eSBR) Tool as signaled in the SBR extension element (bs_extension_id== EXTENSIO- N_ID_ESBR).

[0093] In someembodiments, the invention is amethod including a step of encoding audio data to generate an encoded bitstream (e.g., anMPEG‑4 AACbitstream), including by including eSBRmetadata in at least one segment of at least one block of the encoded bitstream and audio data in at least one other segment of the block. In typical embodiments, the method includes a step of multiplexing the audio data with the eSBRmetadata in each block of the encoded bitstream. In typical decoding of the encoded bitstream in an eSBR decoder, the decoder extracts the eSBR metadata from the bitstream (including by parsing and demultiplexing the eSBRmetadata and the audio data) and uses the eSBRmetadata to process the audio data to generate a stream of decoded audio data.

[0094] Another aspect of the invention is an eSBR decoder configured to perform eSBR processing (e.g., using at least one of the eSBR tools known as harmonic transposition or pre-flattening) during decoding of an encoded audio bitstream (e.g., anMPEG‑4AACbitstream)whichdoesnot includeeSBRmetadata.Anexample of suchadecoderwill bedescribed with reference to Fig. 5.

[0095] TheeSBRdecoder (400) of Fig. 5 includes buffermemory201 (which is identical tomemory201of Figs. 3 and4), bitstream payload deformatter 215 (which is identical to deformatter 215 of Fig. 4), audio decoding subsystem 202 (sometimes referred to as a "core" decoding stage or "core" decoding subsystem, and which is identical to core decoding subsystem 202 of Fig. 3), eSBR control data generation subsystem 401, and eSBR processing stage 203 (which is identical to stage 203 of Fig. 3), connected as shown. Typically also, decoder 400 includes other processing elements (not shown).

[0096] In operation of decoder 400, a sequence of blocks of an encoded audio bitstream (an MPEG‑4 AAC bitstream) received by decoder 400 is asserted from buffer 201 to deformatter 215.

[0097] Deformatter 215 is coupled and configured to demultiplex each block of the bitstream to extract SBR metadata (including quantized envelope data) and typically also other metadata therefrom. Deformatter 215 is configured to assert at least theSBRmetadata to eSBRprocessing stage203.Deformatter 215 is also coupled and configured to extract audio data fromeachblockof thebitstream, and to assert the extractedaudio data to decoding subsystem (decoding stage) 202.

[0098] Audio decoding subsystem 202 of decoder 400 is configured to decode the audio data extracted by deformatter 215 (such decodingmay be referred to as a "core" decoding operation) to generate decoded audio data, and to assert the decoded audio data to eSBR processing stage 203. The decoding is performed in the frequency domain. Typically, a final stage of processing in subsystem 202 applies a frequency domain-to-time domain transform to the decoded frequency domain audio data, so that the output of subsystem is time domain, decoded audio data. Stage 203 is configured to apply SBR tools (and eSBR tools) indicated by the SBR metadata (extracted by deformatter 215) and by eSBR metadata generated in subsystem 401, to the decoded audio data (i.e., to perform SBR and eSBR processing on the output of decoding subsystem 202 using the SBR and eSBR metadata) to generate the fully decoded audio data which is output from decoder 400. Typically, decoder 400 includes amemory (accessible by subsystem 202 and stage 203) which stores thedeformattedaudio dataandmetadataoutput fromdeformatter 215 (andoptionally also subsystem401), andstage203 is configured toaccess theaudio data andmetadata asneededduringSBRandeSBRprocessing. TheSBRprocessing in stage 203 may be considered to be post-processing on the output of core decoding subsystem 202. Optionally, decoder 400also includesa final upmixing subsystem (whichmayapply parametric stereo ("PS") tools defined in theMPEG‑4AAC standard, using PSmetadata extracted by deformatter 215) which is coupled and configured to perform upmixing on the output of stage 203 to generated fully decoded, upmixed audio which is output from APU 210.

[0099] Control data generation subsystem 401 of Fig. 5 is coupled and configured to detect at least one property of the encoded audio bitstream to be decoded, and to generate eSBR control data (which may be or include eSBRmetadata of anyof the types included in encodedaudio bitstreams in accordancewith other embodiments of the invention) in response toat least one result of thedetection step.TheeSBRcontrol data is asserted to stage203 to trigger applicationof individual eSBR tools or combinations of eSBR tools upon detecting a specific property (or combination of properties) of the 14 EP 4 756 801 A1 5 10 15 20 25 30 35 40 45 50 55 bitstream, and / or to control the application of such eSBR tools. For example, in order to control performance of eSBR processing using harmonic transposition, some embodiments of control data generation subsystem 401would include: a music detector (e.g., a simplified version of a conventionalmusic detector) for setting the sbrPatchingMode[ch] parameter (and asserting the set parameter to stage 203) in response to detecting that the bitstream is or is not indicative of music; a transient detector for setting the sbrOversamplingFlag[ch] parameter (and asserting the set parameter to stage 203) in response to detecting the presence or absence of transients in the audio content indicated by the bitstream; and / or a pitch detector for setting the sbrPitchInBinsFlag[ch] and sbrPitchinBins[ch] parameters (and asserting the set parameters to stage203) in response to detecting the pitch of audio content indicated by thebitstream.Other aspects of the invention are audio bitstream decoding methods performed by any embodiment of the inventive decoder described in this paragraph and the preceding paragraph.

[0100] Aspects of the invention include an encoding or decoding method of the type which any embodiment of the inventive APU, system or device is configured (e.g., programmed) to perform. Other aspects of the invention include a system or device configured (e.g., programmed) to perform any embodiment of the inventive method, and a computer readable medium (e.g., a disc) which stores code (e.g., in a non-transitory manner) for implementing any embodiment of the inventive method or steps thereof. For example, the inventive system can be or include a programmable general purpose processor, digital signal processor, or microprocessor, programmed with software or firmware and / or otherwise configured to perform any of a variety of operations on data, including an embodiment of the inventive method or steps thereof. Suchageneral purposeprocessormaybeor includea computer system includingan input device, amemory, and processing circuitry programmed (and / or otherwise configured) to perform an embodiment of the inventive method (or steps thereof) in response to data asserted thereto.

[0101] Embodiments of the present inventionmaybe implemented in hardware, firmware, or software, or a combination of both (e.g., as a programmable logic array). Unless otherwise specified, the algorithms or processes included as part of the invention are not inherently related to any particular computer or other apparatus. In particular, various general- purpose machines may be used with programs written in accordance with the teachings herein, or it may be more convenient to constructmore specialized apparatus (e.g., integrated circuits) to perform the requiredmethod steps. Thus, the inventionmay be implemented in one ormore computer programs executing on one ormore programmable computer systems (e.g., an implementation of any of the elements of Fig. 1, or encoder 100 of Fig. 2 (or an element thereof), or decoder 200 of Fig. 3 (or an element thereof), or decoder 210 of Fig. 4 (or an element thereof), or decoder 400 of Fig. 5 (or an element thereof)) each comprising at least one processor, at least one data storage system (including volatile and non- volatilememory and / or storageelements), at least one input device or port, andat least oneoutput device or port. Program code is applied to input data to perform the functions described herein and generate output information. The output information is applied to one or more output devices, in known fashion.

[0102] Each such program may be implemented in any desired computer language (including machine, assembly, or high level procedural, logical, or object oriented programming languages) to communicatewith a computer system. In any case, the language may be a compiled or interpreted language.

[0103] For example, when implemented by computer software instruction sequences, various functions and steps of embodiments of the invention may be implemented by multithreaded software instruction sequences running in suitable digital signal processing hardware, in which case the various devices, steps, and functions of the embodiments may correspond to portions of the software instructions.

[0104] Eachsuchcomputer program ispreferably storedonordownloaded toastoragemediaor device (e.g., solid state memory or media, or magnetic or optical media) readable by a general or special purpose programmable computer, for configuring and operating the computer when the storagemedia or device is read by the computer system to perform the procedures described herein. The inventive systemmay also be implemented as a computer-readable storage medium, configuredwith (i.e., storing) a computer program,where the storagemediumso configured causes a computer system to operate in a specific and predefined manner to perform the functions described herein.

[0105] Anumber of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Numerous modifications and variations of the present invention are possible in light of the above teachings. For example, in order to facilitate efficient implementations, phase-shiftsmaybeused in combinationwith the complexQMFanalysis and synthesis filter banks. The analysis filterbank is responsible for filtering the time-domain lowband signal generated by the core decoder into a plurality of subbands (e.g., QMF subbands). The synthesis filterbank is responsible for combining the regenerated highband produced by the selected HFR technique (as indicated by the received sbrPatchingMode parameter) with the decoded lowband to produce a wideband output audio signal. A given filterbank implementation operating in a certain sample-rate mode, e.g., normal dual-rate operation or down-sampled SBR mode, should not, however, have phase-shifts that are bitstreamdependent.TheQMFbanksused inSBRareacomplex-exponential extensionof the theoryof cosinemodulated filter banks. It can be shown that alias cancellation constraints become obsolete when extending the cosine modulated filterbank with complex-exponential modulation. Thus, for the SBR QMF banks, both the analysis filters, hk(n), and synthesis filters, fk(n), may be defined by: 15 EP 4 756 801 A1 5 10 15 20 25 30 35 40 45 50 55 where p0(n) is a real-valued symmetric or asymmetric prototype filter (typically, a lowpass prototype filter), M denotes the number of channels and N is the prototype filter order. The number of channels used in the analysis filterbank may be different than the number of channel used in the synthesis filterbank. For example, the analysis filterbank may have 32 channels and the synthesis filterbank may have 64 channels. When operating the synthesis filterbank in down-sampled mode, the synthesis filterbank may have only 32 channels. Since the subband samples from the filter bank are complex- valued, an additive possibly channel-dependent phase-shift stepmay be appended to the analysis filterbank. These extra phase-shifts need tobecompensated forbefore thesynthesis filter bank.While thephase-shifting terms inprinciple canbe of arbitrary valueswithout destroying the operation of theQMFanalysis / synthesis-chain, theymay also be constrained to certain values for conformance verification. TheSBRsignalwill be affected by the choice of the phase factorswhile the low pass signal coming from the core decoder will not. The audio quality of the output signal is not affected.

[0106] The coefficients of the prototype filter, p0(n), may be defined with a length, L, of 640, as shown in Table 4 below. Table 4 n p0(n) n p0(n) n p0(n) 0 0.0000000000 214 0.0019765601 428 0.0117623832 1 ‑0.0005525286 215 ‑0.0032086896 429 0.0163701258 2 ‑0.0005617692 216 ‑0.0085711749 430 0.0207997072 3 ‑0.0004947518 217 ‑0.0141288827 431 0.0250307561 4 ‑0.0004875227 218 ‑0.0198834129 432 0.0290824006 5 ‑0.0004893791 219 ‑0.0258227288 433 0.0329583930 6 ‑0.0005040714 220 ‑0.0319531274 434 0.0366418116 7 ‑0.0005226564 221 ‑0.0382776572 435 0.0401458278 8 ‑0.0005466565 222 ‑0.0447806821 436 0.0434768782 9 ‑0.0005677802 223 ‑0.0514804176 437 0.0466303305 10 ‑0.0005870930 224 ‑0.0583705326 438 0.0495978676 11 ‑0.0006132747 225 ‑0.0654409853 439 0.0524093821 12 ‑0.0006312493 226 ‑0.0726943300 440 0.0550460034 13 ‑0.0006540333 227 ‑0.0801372934 441 0.0575152691 14 ‑0.0006777690 228 ‑0.0877547536 442 0.0598166570 15 ‑0.0006941614 229 ‑0.0955533352 443 0.0619602779 16 ‑0.0007157736 230 ‑0.1035329531 444 0.0639444805 17 ‑0.0007255043 231 ‑0.1116826931 445 0.0657690668 18 ‑0.0007440941 232 ‑0.1200077984 446 0.0674525021 19 ‑0.0007490598 233 ‑0.1285002850 447 0.0689664013 20 ‑0.0007681371 234 ‑0.1371551761 448 0.0703533073 21 ‑0.0007724848 235 ‑0.1459766491 449 0.0715826364 22 ‑0.0007834332 236 ‑0.1549607071 450 0.0726774642 23 ‑0.0007779869 237 ‑0.1640958855 451 0.0736406005 24 ‑0.0007803664 238 ‑0.1733808172 452 0.0744664394 25 ‑0.0007801449 239 ‑0.1828172548 453 0.0751576255 26 ‑0.0007757977 240 ‑0.1923966745 454 0.0757305756 27 ‑0.0007630793 241 ‑0.2021250176 455 0.0761748321 28 ‑0.0007530001 242 ‑0.2119735853 456 0.0765050718 16 EP 4 756 801 A1 5 10 15 20 25 30 35 40 45 50 55 (continued) n p0(n) n p0(n) n p0(n) 29 ‑0.0007319357 243 ‑0.2219652696 457 0.0767204924 30 ‑0.0007215391 244 ‑0.2320690870 458 0.0768230011 31 ‑0.0006917937 245 ‑0.2423016884 459 0.0768173975 32 ‑0.0006650415 246 ‑0.2526480309 460 0.0767093490 33 ‑0.0006341594 247 ‑0.2631053299 461 0.0764992170 34 ‑0.0005946118 248 ‑0.2736634040 462 0.0761992479 35 ‑0.0005564576 249 ‑0.2843214189 463 0.0758008358 36 ‑0.0005145572 250 ‑0.2950716717 464 0.0753137336 37 ‑0.0004606325 251 ‑0.3059098575 465 0.0747452558 38 ‑0.0004095121 252 ‑0.3168278913 466 0.0741003642 39 ‑0.0003501175 253 ‑0.3278113727 467 0.0733620255 40 ‑0.0002896981 254 ‑0.3388722693 468 0.0725682583 41 ‑0.0002098337 255 ‑0.3499914122 469 0.0717002673 42 ‑0.0001446380 256 0.3611589903 470 0.0707628710 43 ‑0.0000617334 257 0.3723795546 471 0.0697630244 44 0.0000134949 258 0.3836350013 472 0.0687043828 45 0.0001094383 259 0.3949211761 473 0.0676075985 46 0.0002043017 260 0.4062317676 474 0.0664367512 47 0.0002949531 261 0.4175696896 475 0.0652247106 48 0.0004026540 262 0.4289119920 476 0.0639715898 49 0.0005107388 263 0.4402553754 477 0.0626857808 50 0.0006239376 264 0.4515996535 478 0.0613455171 51 0.0007458025 265 0.4629308085 479 0.0599837480 52 0.0008608443 266 0.4742453214 480 0.0585915683 53 0.0009885988 267 0.4855253091 481 0.0571616450 54 0.0011250155 268 0.4967708254 482 0.0557173648 55 0.0012577884 269 0.5079817500 483 0.0542452768 56 0.0013902494 270 0.5191234970 484 0.0527630746 57 0.0015443219 271 0.5302240895 485 0.0512556155 58 0.0016868083 272 0.5412553448 486 0.0497385755 59 0.0018348265 273 0.5522051258 487 0.0482165720 60 0.0019841140 274 0.5630789140 488 0.0466843027 61 0.0021461583 275 0.5738524131 489 0.0451488405 62 0.0023017254 276 0.5845403235 490 0.0436097542 63 0.0024625616 277 0.5951123086 491 0.0420649094 64 0.0026201758 278 0.6055783538 492 0.0405349170 65 0.0027870464 279 0.6159109932 493 0.0390053679 66 0.0029469447 280 0.6261242695 494 0.0374812850 67 0.0031125420 281 0.6361980107 495 0.0359697560 17 EP 4 756 801 A1 5 10 15 20 25 30 35 40 45 50 55 (continued) n p0(n) n p0(n) n p0(n) 68 0.0032739613 282 0.6461269695 496 0.0344620948 69 0.0034418874 283 0.6559016302 497 0.0329754081 70 0.0036008268 284 0.6655139880 498 0.0315017608 71 0.0037603922 285 0.6749663190 499 0.0300502657 72 0.0039207432 286 0.6842353293 500 0.0286072173 73 0.0040819753 287 0.6933282376 501 0.0271859429 74 0.0042264269 288 0.7022388719 502 0.0257875847 75 0.0043730719 289 0.7109410426 503 0.0244160992 76 0.0045209852 290 0.7194462634 504 0.0230680169 77 0.0046606460 291 0.7277448900 505 0.0217467550 78 0.0047932560 292 0.7358211758 506 0.0204531793 79 0.0049137603 293 0.7436827863 507 0.0191872431 80 0.0050393022 294 0.7513137456 508 0.0179433381 81 0.0051407353 295 0.7587080760 509 0.0167324712 82 0.0052461166 296 0.7658674865 510 0.0155405553 83 0.0053471681 297 0.7727780881 511 0.0143904666 84 0.0054196775 298 0.7794287519 512 ‑0.0132718220 85 0.0054876040 299 0.7858353120 513 ‑0.0121849995 86 0.0055475714 300 0.7919735841 514 ‑0.0111315548 87 0.0055938023 301 0.7978466413 515 ‑0.0101150215 88 0.0056220643 302 0.8034485751 516 ‑0.0091325329 89 0.0056455196 303 0.8087695004 517 ‑0.0081798233 90 0.0056389199 304 0.8138191270 518 ‑0.0072615816 91 0.0056266114 305 0.8185776004 519 ‑0.0063792293 92 0.0055917128 306 0.8230419890 520 ‑0.0055337211 93 0.0055404363 307 0.8272275347 521 ‑0.0047222596 94 0.0054753783 308 0.8311038457 522 ‑0.0039401124 95 0.0053838975 309 0.8346937361 523 ‑0.0031933778 96 0.0052715758 310 0.8379717337 524 ‑0.0024826723 97 0.0051382275 311 0.8409541392 525 ‑0.0018039472 98 0.0049839687 312 0.8436238281 526 ‑0.0011568135 99 0.0048109469 313 0.8459818469 527 ‑0.0005464280 100 0.0046039530 314 0.8480315777 528 0.0000276045 101 0.0043801861 315 0.8497805198 529 0.0005832264 102 0.0041251642 316 0.8511971524 530 0.0010902329 103 0.0038456408 317 0.8523047035 531 0.0015784682 104 0.0035401246 318 0.8531020949 532 0.0020274176 105 0.0032091885 319 0.8535720573 533 0.0024508540 106 0.0028446757 320 0.8537385600 534 0.0028446757 18 EP 4 756 801 A1 5 10 15 20 25 30 35 40 45 50 55 (continued) n p0(n) n p0(n) n p0(n) 107 0.0024508540 321 0.8535720573 535 0.0032091885 108 0.0020274176 322 0.8531020949 536 0.0035401246 109 0.0015784682 323 0.8523047035 537 0.0038456408 110 0.0010902329 324 0.8511971524 538 0.0041251642 111 0.0005832264 325 0.8497805198 539 0.0043801861 112 0.0000276045 326 0.8480315777 540 0.0046039530 113 ‑0.0005464280 327 0.8459818469 541 0.0048109469 114 ‑0.0011568135 328 0.8436238281 542 0.0049839687 115 ‑0.0018039472 329 0.8409541392 543 0.0051382275 116 ‑0.0024826723 330 0.8379717337 544 0.0052715758 117 ‑0.0031933778 331 0.8346937361 545 0.0053838975 118 ‑0.0039401124 332 0.8311038457 546 0.0054753783 119 ‑0.0047222596 333 0.8272275347 547 0.0055404363 120 ‑0.0055337211 334 0.8230419890 548 0.0055917128 121 ‑0.0063792293 335 0.8185776004 549 0.0056266114 122 ‑0.0072615816 336 0.8138191270 550 0.0056389199 123 ‑0.0081798233 337 0.8087695004 551 0.0056455196 124 ‑0.0091325329 338 0.8034485751 552 0.0056220643 125 ‑0.0101150215 339 0.7978466413 553 0.0055938023 126 ‑0.0111315548 340 0.7919735841 554 0.0055475714 127 ‑0.0121849995 341 0.7858353120 555 0.0054876040 128 0.0132718220 342 0.7794287519 556 0.0054196775 129 0.0143904666 343 0.7727780881 557 0.0053471681 130 0.0155405553 344 0.7658674865 558 0.0052461166 131 0.0167324712 345 0.7587080760 559 0.0051407353 132 0.0179433381 346 0.7513137456 560 0.0050393022 133 0.0191872431 347 0.7436827863 561 0.0049137603 134 0.0204531793 348 0.7358211758 562 0.0047932560 135 0.0217467550 349 0.7277448900 563 0.0046606460 136 0.0230680169 350 0.7194462634 564 0.0045209852 137 0.0244160992 351 0.7109410426 565 0.0043730719 138 0.0257875847 352 0.7022388719 566 0.0042264269 139 0.0271859429 353 0.6933282376 567 0.0040819753 140 0.0286072173 354 0.6842353293 568 0.0039207432 141 0.0300502657 355 0.6749663190 569 0.0037603922 142 0.0315017608 356 0.6655139880 570 0.0036008268 143 0.0329754081 357 0.6559016302 571 0.0034418874 144 0.0344620948 358 0.6461269695 572 0.0032739613 145 0.0359697560 359 0.6361980107 573 0.0031125420 19 EP 4 756 801 A1 5 10 15 20 25 30 35 40 45 50 55 (continued) n p0(n) n p0(n) n p0(n) 146 0.0374812850 360 0.6261242695 574 0.0029469447 147 0.0390053679 361 0.6159109932 575 0.0027870464 148 0.0405349170 362 0.6055783538 576 0.0026201758 149 0.0420649094 363 0.5951123086 577 0.0024625616 150 0.0436097542 364 0.5845403235 578 0.0023017254 151 0.0451488405 365 0.5738524131 579 0.0021461583 152 0.0466843027 366 0.5630789140 580 0.0019841140 153 0.0482165720 367 0.5522051258 581 0.0018348265 154 0.0497385755 368 0.5412553448 582 0.0016868083 155 0.0512556155 369 0.5302240895 583 0.0015443219 156 0.0527630746 370 0.5191234970 584 0.0013902494 157 0.0542452768 371 0.5079817500 585 0.0012577884 158 0.0557173648 372 0.4967708254 586 0.0011250155 159 0.0571616450 373 0.4855253091 587 0.0009885988 160 0.0585915683 374 0.4742453214 588 0.0008608443 161 0.0599837480 375 0.4629308085 589 0.0007458025 162 0.0613455171 376 0.4515996535 590 0.0006239376 163 0.0626857808 377 0.4402553754 591 0.0005107388 164 0.0639715898 378 0.4289119920 592 0.0004026540 165 0.0652247106 379 0.4175696896 593 0.0002949531 166 0.0664367512 380 0.4062317676 594 0.0002043017 167 0.0676075985 381 0.3949211761 595 0.0001094383 168 0.0687043828 382 0.3836350013 596 0.0000134949 169 0.0697630244 383 0.3723795546 597 ‑0.0000617334 170 0.0707628710 384 ‑0.3611589903 598 ‑0.0001446380 171 0.0717002673 385 ‑0.3499914122 599 ‑0.0002098337 172 0.0725682583 386 ‑0.3388722693 600 ‑0.0002896981 173 0.0733620255 387 ‑0.3278113727 601 ‑0.0003501175 174 0.0741003642 388 ‑0.3168278913 602 ‑0.0004095121 175 0.0747452558 389 ‑0.3059098575 603 ‑0.0004606325 176 0.0753137336 390 ‑0.2950716717 604 ‑0.0005145572 177 0.0758008358 391 ‑0.2843214189 605 ‑0.0005564576 178 0.0761992479 392 ‑0.2736634040 606 ‑0.0005946118 179 0.0764992170 393 ‑0.2631053299 607 ‑0.0006341594 180 0.0767093490 394 ‑0.2526480309 608 ‑0.0006650415 181 0.0768173975 395 ‑0.2423016884 609 ‑0.0006917937 182 0.0768230011 396 ‑0.2320690870 610 ‑0.0007215391 183 0.0767204924 397 ‑0.2219652696 611 ‑0.0007319357 184 0.0765050718 398 ‑0.2119735853 612 ‑0.0007530001 20 EP 4 756 801 A1 5 10 15 20 25 30 35 40 45 50 55 (continued) n p0(n) n p0(n) n p0(n) 185 0.0761748321 399 ‑0.2021250176 613 ‑0.0007630793 186 0.0757305756 400 ‑0.1923966745 614 ‑0.0007757977 187 0.0751576255 401 ‑0.1828172548 615 ‑0.0007801449 188 0.0744664394 402 ‑0.1733808172 616 ‑0.0007803664 189 0.0736406005 403 ‑0.1640958855 617 ‑0.0007779869 190 0.0726774642 404 ‑0.1549607071 618 ‑0.0007834332 191 0.0715826364 405 ‑0.1459766491 619 ‑0.0007724848 192 0.0703533073 406 ‑0.1371551761 620 ‑0.0007681371 193 0.0689664013 407 ‑0.1285002850 621 ‑0.0007490598 194 0.0674525021 408 ‑0.1200077984 622 ‑0.0007440941 195 0.0657690668 409 ‑0.1116826931 623 ‑0.0007255043 196 0.0639444805 410 ‑0.1035329531 624 ‑0.0007157736 197 0.0619602779 411 ‑0.0955533352 625 ‑0.0006941614 198 0.0598166570 412 ‑0.0877547536 626 ‑0.0006777690 199 0.0575152691 413 ‑0.0801372934 627 ‑0.0006540333 200 0.0550460034 414 ‑0.0726943300 628 ‑0.0006312493 201 0.0524093821 415 ‑0.0654409853 629 ‑0.0006132747 202 0.0495978676 416 ‑0.0583705326 630 ‑0.0005870930 203 0.0466303305 417 ‑0.0514804176 631 ‑0.0005677802 204 0.0434768782 418 ‑0.0447806821 632 ‑0.0005466565 205 0.0401458278 419 ‑0.0382776572 633 ‑0.0005226564 206 0.0366418116 420 ‑0.0319531274 634 ‑0.0005040714 207 0.0329583930 421 ‑0.0258227288 635 ‑0.0004893791 208 0.0290824006 422 ‑0.0198834129 636 ‑0.0004875227 209 0.0250307561 423 ‑0.0141288827 637 ‑0.0004947518 210 0.0207997072 424 ‑0.0085711749 638 ‑0.0005617692 211 0.0163701258 425 ‑0.0032086896 639 ‑0.0005525280 212 0.0117623832 426 0.0019765601 213 0.0069636862 427 0.0069636862 The prototype filter, p0(n), may also be derived from Table 4 by one or more mathematical operations such as round- ing, subsampling, interpolation, and decimation.

[0107] It is to beunderstood thatwithin the scopeof the appendedclaims, the inventionmaybepracticed otherwise than asspecifically describedherein.Any referencenumerals contained in the followingclaimsare for illustrativepurposesonly and should not be used to construe or limit the claims in any manner whatsoever.

[0108] Various aspects and implementations of the present invention may be appreciated from the following enum- erated example embodiments (EEEs), which are not claims: EEE1. A method for decoding an encoded audio bitstream, the method comprising: receiving the encoded audio bitstream, the encoded audio bitstream including audio data representing a lowband portion of an audio signal; decoding the audio data to generate a decoded lowband audio signal; extracting from the encoded audio bitstream high frequency reconstruction metadata, the high frequency 21 EP 4 756 801 A1 5 10 15 20 25 30 35 40 45 50 55 reconstructionmetadata including operating parameters for a high frequency reconstruction process that linearly translates a consecutive number of subbands from a lowband portion of the audio signal to a highband portion of the audio signal; filtering the decoded lowband audio signal with an analysis filterbank to generate a filtered lowband audio signal; extracting from the encoded audio bitstream a flag indicating whether either linear translation or harmonic transposition is to be performed on the audio data; regeneratingahighbandportion of theaudio signal using the filtered lowbandaudio signal and thehigh frequency reconstruction metadata in accordance with the flag; and combining the filtered lowband audio signal and the regenerated highband portion to form a wideband audio signal. EEE2. The method of EEE1 wherein the encoded audio bitstream further includes a fill element with an identifier indicating a start of the fill element and fill data after the identifier, wherein the fill data includes the flag. EEE3. The method of EEE2 wherein the identifier is a three bit unsigned integer transmitted most significant bit first and having a value of 0x6. EEE4. The method of EEE2, wherein the fill data includes an extension payload, the extension payload includes spectral band replication extension data, and the extension payload is identified with a four bit unsigned integer transmitted most significant bit first and having a value of ’1101’ or ’1110’, and, optionally, wherein the spectral band replication extension data includes: an optional spectral band replication header, spectral band replication data after the header, an spectral band replication extension element after the spectral band replication data, and wherein the flag is included in the spectral band replication extension element. EEE5. The method of any one of EEE1-EEE4 wherein the high frequency reconstruction metadata includes an operating parameter selected from the group consisting of envelope scalefactors, noise floor scale factors, sinusoid addition information, time / frequency grid information, crossover frequency, and inverse filtering mode. EEE6. The method of any one of EEE1-EEE4 wherein the analysis filterbank includes analysis filters, hk(n), that are modulated versions of a prototype filter, p0(n), according to: where p0(n) is a real-valued symmetric or asymmetric prototype filter, M is a number of channels in the analysis filterbank and N is the prototype filter order. EEE7. The method of EEE6 wherein the prototype filter, p0(n), is derived from coefficients of Table 4. EEE8. The method of EEE6 wherein the prototype filter, p0(n), is derived from coefficients of Table 4 by one or more mathematical operations selected from the group consisting of rounding, subsampling, interpolation, or decimation. EEE9. Themethod of any one of EEE1-EEE8wherein a phase shift is added to the filtered lowband audio signal after the filtering and compensated for before the combining. EEE10. A non-transitory computer readable medium containing instructions that when executed by a processor perform the method of EEE1. EEE11. A decoder for decoding an encoded audio bitstream, the decoder comprising: an input interface for receiving the encoded audio bitstream, the encoded audio bitstream including audio data representing a lowband portion of an audio signal; a core decoder for decoding the audio data to generate a decoded lowband audio signal; a deformatter for extracting from the encoded audio bitstream high frequency reconstruction metadata, the high frequency reconstruction metadata including operating parameters for a high frequency reconstruction process that linearly translates a consecutive number of subbands from a lowband portion of the audio signal to a highband portion of the audio signal; an analysis filterbank for filtering the decoded lowband audio signal to generate a filtered lowband audio signal; a deformatter for extracting from the encoded audio bitstreama flag indicatingwhether either linear translation or harmonic transposition is to be performed on the audio data; a high frequency regenerator for regenerating a highbandportionof the audio signal using the filtered lowbandaudio signal and thehigh frequency reconstruction metadata in accordance with the flag; and a synthesis filterbank for combining the filtered lowband audio signal and the regenerated highband portion to form a wideband audio signal. 22 EP 4 756 801 A1 5 10 15 20 25 30 35 40 45 50 55 EEE12. The decoder of EEE11 wherein the encoded audio bitstream further includes a fill element with an identifier indicating a start of the fill element and fill data after the identifier, wherein the fill data includes the flag. EEE13.Thedecoder ofEEE12wherein the identifier is a threebit unsigned integer transmittedmost significant bit first and having a value of 0x6. EEE14. The decoder of EEE12, wherein the fill data includes an extension payload, the extension payload includes spectral band replication extension data, and the extension payload is identified with a four bit unsigned integer transmitted most significant bit first and having a value of ’1101’ or ’1110’, and, optionally, wherein the spectral band replication extension data includes: an optional spectral band replication header, spectral band replication data after the header, an spectral band replication extension element after the spectral band replication data, and wherein the flag is included in the spectral band replication extension element. EEE15. The decoder of any one of EEE11-EEE14 wherein the high frequency reconstruction metadata includes an operating parameter selected from the group consisting of envelope scalefactors, noise floor scale factors, sinusoid addition information, time / frequency grid information, crossover frequency, and inverse filtering mode. EEE16. The decoder of any one of EEE11-EEE14 wherein the analysis filterbank includes analysis filters, hk(n), that are modulated versions of a prototype filter, p0(n), according to: where p0(n) is a real-valued symmetric or asymmetric prototype filter, M is a number of channels in the analysis filterbank and N is the prototype filter order. EEE17. The decoder of EEE16 wherein the prototype filter, p0(n), is derived from coefficients of Table 4. EEE18.Thedecoder ofEEE16wherein theprototypefilter, p0(n), is derived fromcoefficients of Table 4byoneormore mathematical operations selected from the group consisting of rounding, subsampling, interpolation, or decimation. EEE19. The decoder of any one of EEE11-EEE18 wherein a phase shift is added to the filtered lowband audio signal after the filtering and compensated for before the combining. Claims 1. A method for decoding an encoded audio bitstream, the method comprising: receiving theencodedaudio bitstream, theencodedaudio bitstream includingaudio data representinga lowband portion of an audio signal; decoding the audio data to generate a decoded lowband audio signal; extracting from the encoded audio bitstream high frequency reconstruction metadata, the high frequency reconstructionmetadata including operating parameters for a high frequency reconstruction process that linearly translates a consecutive number of subbands from a lowband portion of the audio signal to a highband portion of the audio signal; filtering the decoded lowband audio signal with an analysis filterbank to generate a filtered lowband audio signal; extracting from the encoded audio bitstream a flag indicating whether either linear translation or harmonic transposition is to be performed on the audio data; extracting from the encoded audio bitstream a parameter indicating whether to use signal adaptive frequency domain oversampling; wherein the encoded audio bitstream further includes a fill element with an identifier indicating a start of the fill element and fill data after the identifier, wherein the fill data includes the flag; wherein the fill data includes an extension payload, the extension payload includes spectral band replication extensiondata, and theextensionpayload is identifiedwitha four bit unsigned integer transmittedmost significant bit first and having a value of ’1101’ or ’1110’, wherein the identifier is a three bit unsigned integer transmittedmost significant bit first and having a value of 0x6; if the flag indicates that harmonic transposition is to be performed on the audio data: regenerating a highband portion of the audio signal by performing harmonic transposition using the filtered lowband audio signal and the high frequency reconstruction metadata; and 23 EP 4 756 801 A1 5 10 15 20 25 30 35 40 45 50 55 combining the filtered lowband audio signal and the regenerated highband portion to form awideband audio signal, wherein a phase shift is added to the filtered lowband audio signal after the filtering and compensated for before the combining, characterized in that the analysis filterbank includes analysis filters, hk(n), that aremodulated versions of a prototype filter, p0(n), according to: where p0(n) is a real-valued symmetric or asymmetric prototype filter, M is a number of channels in the analysis filterbank and N is the prototype filter order; wherein the prototype filter, p0(n), is defined by the coefficients of the following Table: n p0(n) n p0(n) n p0(n) 0 0.0000000000 214 0.0019765601 428 0.0117623832 1 ‑0.0005525286 215 ‑0.0032086896 429 0.0163701258 2 ‑0.0005617692 216 ‑0.0085711749 430 0.0207997072 3 ‑0.0004947518 217 ‑0.0141288827 431 0.0250307561 4 ‑0.0004875227 218 ‑0.0198834129 432 0.0290824006 5 ‑0.0004893791 219 ‑0.0258227288 433 0.0329583930 6 ‑0.0005040714 220 ‑0.0319531274 434 0.0366418116 7 ‑0.0005226564 221 ‑0.0382776572 435 0.0401458278 8 ‑0.0005466565 222 ‑0.0447806821 436 0.0434768782 9 ‑0.0005677802 223 ‑0.0514804176 437 0.0466303305 10 ‑0.0005870930 224 ‑0.0583705326 438 0.0495978676 11 ‑0.0006132747 225 ‑0.0654409853 439 0.0524093821 12 ‑0.0006312493 226 ‑0.0726943300 440 0.0550460034 13 ‑0.0006540333 227 ‑0.0801372934 441 0.0575152691 14 ‑0.0006777690 228 ‑0.0877547536 442 0.0598166570 15 ‑0.0006941614 229 ‑0.0955533352 443 0.0619602779 16 ‑0.0007157736 230 ‑0.1035329531 444 0.0639444805 17 ‑0.0007255043 231 ‑0.1116826931 445 0.0657690668 18 ‑0.0007440941 232 ‑0.1200077984 446 0.0674525021 19 ‑0.0007490598 233 ‑0.1285002850 447 0.0689664013 20 ‑0.0007681371 234 ‑0.1371551761 448 0.0703533073 21 ‑0.0007724848 235 ‑0.1459766491 449 0.0715826364 22 ‑0.0007834332 236 ‑0.1549607071 450 0.0726774642 23 ‑0.0007779869 237 ‑0.1640958855 451 0.0736406005 24 ‑0.0007803664 238 ‑0.1733808172 452 0.0744664394 25 ‑0.0007801449 239 ‑0.1828172548 453 0.0751576255 26 ‑0.0007757977 240 ‑0.1923966745 454 0.0757305756 27 ‑0.0007630793 241 ‑0.2021250176 455 0.0761748321 28 ‑0.0007530001 242 ‑0.2119735853 456 0.0765050718 29 ‑0.0007319357 243 ‑0.2219652696 457 0.0767204924 30 ‑0.0007215391 244 ‑0.2320690870 458 0.0768230011 24 EP 4 756 801 A1 5 10 15 20 25 30 35 40 45 50 55 (continued) n p0(n) n p0(n) n p0(n) 31 ‑0.0006917937 245 ‑0.2423016884 459 0.0768173975 32 ‑0.0006650415 246 ‑0.2526480309 460 0.0767093490 33 ‑0.0006341594 247 ‑0.2631053299 461 0.0764992170 34 ‑0.0005946118 248 ‑0.2736634040 462 0.0761992479 35 ‑0.0005564576 249 ‑0.2843214189 463 0.0758008358 36 ‑0.0005145572 250 ‑0.2950716717 464 0.0753137336 37 ‑0.0004606325 251 ‑0.3059098575 465 0.0747452558 38 ‑0.0004095121 252 ‑0.3168278913 466 0.0741003642 39 ‑0.0003501175 253 ‑0.3278113727 467 0.0733620255 40 ‑0.0002896981 254 ‑0.3388722693 468 0.0725682583 41 ‑0.0002098337 255 ‑0.3499914122 469 0.0717002673 42 ‑0.0001446380 256 0.3611589903 470 0.0707628710 43 ‑0.0000617334 257 0.3723795546 471 0.0697630244 44 0.0000134949 258 0.3836350013 472 0.0687043828 45 0.0001094383 259 0.3949211761 473 0.0676075985 46 0.0002043017 260 0.4062317676 474 0.0664367512 47 0.0002949531 261 0.4175696896 475 0.0652247106 48 0.0004026540 262 0.4289119920 476 0.0639715898 49 0.0005107388 263 0.4402553754 477 0.0626857808 50 0.0006239376 264 0.4515996535 478 0.0613455171 51 0.0007458025 265 0.4629308085 479 0.0599837480 52 0.0008608443 266 0.4742453214 480 0.0585915683 53 0.0009885988 267 0.4855253091 481 0.0571616450 54 0.0011250155 268 0.4967708254 482 0.0557173648 55 0.0012577884 269 0.5079817500 483 0.0542452768 56 0.0013902494 270 0.5191234970 484 0.0527630746 57 0.0015443219 271 0.5302240895 485 0.0512556155 58 0.0016868083 272 0.5412553448 486 0.0497385755 59 0.0018348265 273 0.5522051258 487 0.0482165720 60 0.0019841140 274 0.5630789140 488 0.0466843027 61 0.0021461583 275 0.5738524131 489 0.0451488405 62 0.0023017254 276 0.5845403235 490 0.0436097542 63 0.0024625616 277 0.5951123086 491 0.0420649094 64 0.0026201758 278 0.6055783538 492 0.0405349170 65 0.0027870464 279 0.6159109932 493 0.0390053679 66 0.0029469447 280 0.6261242695 494 0.0374812850 67 0.0031125420 281 0.6361980107 495 0.0359697560 68 0.0032739613 282 0.6461269695 496 0.0344620948 69 0.0034418874 283 0.6559016302 497 0.0329754081 25 EP 4 756 801 A1 5 10 15 20 25 30 35 40 45 50 55 (continued) n p0(n) n p0(n) n p0(n) 70 0.0036008268 284 0.6655139880 498 0.0315017608 71 0.0037603922 285 0.6749663190 499 0.0300502657 72 0.0039207432 286 0.6842353293 500 0.0286072173 73 0.0040819753 287 0.6933282376 501 0.0271859429 74 0.0042264269 288 0.7022388719 502 0.0257875847 75 0.0043730719 289 0.7109410426 503 0.0244160992 76 0.0045209852 290 0.7194462634 504 0.0230680169 77 0.0046606460 291 0.7277448900 505 0.0217467550 78 0.0047932560 292 0.7358211758 506 0.0204531793 79 0.0049137603 293 0.7436827863 507 0.0191872431 80 0.0050393022 294 0.7513137456 508 0.0179433381 81 0.0051407353 295 0.7587080760 509 0.0167324712 82 0.0052461166 296 0.7658674865 510 0.0155405553 83 0.0053471681 297 0.7727780881 511 0.0143904666 84 0.0054196775 298 0.7794287519 512 ‑0.0132718220 85 0.0054876040 299 0.7858353120 513 ‑0.0121849995 86 0.0055475714 300 0.7919735841 514 ‑0.0111315548 87 0.0055938023 301 0.7978466413 515 ‑0.0101150215 88 0.0056220643 302 0.8034485751 516 ‑0.0091325329 89 0.0056455196 303 0.8087695004 517 ‑0.0081798233 90 0.0056389199 304 0.8138191270 518 ‑0.0072615816 91 0.0056266114 305 0.8185776004 519 ‑0.0063792293 92 0.0055917128 306 0.8230419890 520 ‑0.0055337211 93 0.0055404363 307 0.8272275347 521 ‑0.0047222596 94 0.0054753783 308 0.8311038457 522 ‑0.0039401124 95 0.0053838975 309 0.8346937361 523 ‑0.0031933778 96 0.0052715758 310 0.8379717337 524 ‑0.0024826723 97 0.0051382275 311 0.8409541392 525 ‑0.0018039472 98 0.0049839687 312 0.8436238281 526 ‑0.0011568135 99 0.0048109469 313 0.8459818469 527 ‑0.0005464280 100 0.0046039530 314 0.8480315777 528 0.0000276045 101 0.0043801861 315 0.8497805198 529 0.0005832264 102 0.0041251642 316 0.8511971524 530 0.0010902329 103 0.0038456408 317 0.8523047035 531 0.0015784682 104 0.0035401246 318 0.8531020949 532 0.0020274176 105 0.0032091885 319 0.8535720573 533 0.0024508540 106 0.0028446757 320 0.8537385600 534 0.0028446757 107 0.0024508540 321 0.8535720573 535 0.0032091885 108 0.0020274176 322 0.8531020949 536 0.0035401246 26 EP 4 756 801 A1 5 10 15 20 25 30 35 40 45 50 55 (continued) n p0(n) n p0(n) n p0(n) 109 0.0015784682 323 0.8523047035 537 0.0038456408 110 0.0010902329 324 0.8511971524 538 0.0041251642 111 0.0005832264 325 0.8497805198 539 0.0043801861 112 0.0000276045 326 0.8480315777 540 0.0046039530 113 ‑0.0005464280 327 0.8459818469 541 0.0048109469 114 ‑0.0011568135 328 0.8436238281 542 0.0049839687 115 ‑0.0018039472 329 0.8409541392 543 0.0051382275 116 ‑0.0024826723 330 0.8379717337 544 0.0052715758 117 ‑0.0031933778 331 0.8346937361 545 0.0053838975 118 ‑0.0039401124 332 0.8311038457 546 0.0054753783 119 ‑0.0047222596 333 0.8272275347 547 0.0055404363 120 ‑0.0055337211 334 0.8230419890 548 0.0055917128 121 ‑0.0063792293 335 0.8185776004 549 0.0056266114 122 ‑0.0072615816 336 0.8138191270 550 0.0056389199 123 ‑0.0081798233 337 0.8087695004 551 0.0056455196 124 ‑0.0091325329 338 0.8034485751 552 0.0056220643 125 ‑0.0101150215 339 0.7978466413 553 0.0055938023 126 ‑0.0111315548 340 0.7919735841 554 0.0055475714 127 ‑0.0121849995 341 0.7858353120 555 0.0054876040 128 0.0132718220 342 0.7794287519 556 0.0054196775 129 0.0143904666 343 0.7727780881 557 0.0053471681 130 0.0155405553 344 0.7658674865 558 0.0052461166 131 0.0167324712 345 0.7587080760 559 0.0051407353 132 0.0179433381 346 0.7513137456 560 0.0050393022 133 0.0191872431 347 0.7436827863 561 0.0049137603 134 0.0204531793 348 0.7358211758 562 0.0047932560 135 0.0217467550 349 0.7277448900 563 0.0046606460 136 0.0230680169 350 0.7194462634 564 0.0045209852 137 0.0244160992 351 0.7109410426 565 0.0043730719 138 0.0257875847 352 0.7022388719 566 0.0042264269 139 0.0271859429 353 0.6933282376 567 0.0040819753 140 0.0286072173 354 0.6842353293 568 0.0039207432 141 0.0300502657 355 0.6749663190 569 0.0037603922 142 0.0315017608 356 0.6655139880 570 0.0036008268 143 0.0329754081 357 0.6559016302 571 0.0034418874 144 0.0344620948 358 0.6461269695 572 0.0032739613 145 0.0359697560 359 0.6361980107 573 0.0031125420 146 0.0374812850 360 0.6261242695 574 0.0029469447 147 0.0390053679 361 0.6159109932 575 0.0027870464 27 EP 4 756 801 A1 5 10 15 20 25 30 35 40 45 50 55 (continued) n p0(n) n p0(n) n p0(n) 148 0.0405349170 362 0.6055783538 576 0.0026201758 149 0.0420649094 363 0.5951123086 577 0.0024625616 150 0.0436097542 364 0.5845403235 578 0.0023017254 151 0.0451488405 365 0.5738524131 579 0.0021461583 152 0.0466843027 366 0.5630789140 580 0.0019841140 153 0.0482165720 367 0.5522051258 581 0.0018348265 154 0.0497385755 368 0.5412553448 582 0.0016868083 155 0.0512556155 369 0.5302240895 583 0.0015443219 156 0.0527630746 370 0.5191234970 584 0.0013902494 157 0.0542452768 371 0.5079817500 585 0.0012577884 158 0.0557173648 372 0.4967708254 586 0.0011250155 159 0.0571616450 373 0.4855253091 587 0.0009885988 160 0.0585915683 374 0.4742453214 588 0.0008608443 161 0.0599837480 375 0.4629308085 589 0.0007458025 162 0.0613455171 376 0.4515996535 590 0.0006239376 163 0.0626857808 377 0.4402553754 591 0.0005107388 164 0.0639715898 378 0.4289119920 592 0.0004026540 165 0.0652247106 379 0.4175696896 593 0.0002949531 166 0.0664367512 380 0.4062317676 594 0.0002043017 167 0.0676075985 381 0.3949211761 595 0.0001094383 168 0.0687043828 382 0.3836350013 596 0.0000134949 169 0.0697630244 383 0.3723795546 597 ‑0.0000617334 170 0.0707628710 384 ‑0.3611589903 598 ‑0.0001446380 171 0.0717002673 385 ‑0.3499914122 599 ‑0.0002098337 172 0.0725682583 386 ‑0.3388722693 600 ‑0.0002896981 173 0.0733620255 387 ‑0.3278113727 601 ‑0.0003501175 174 0.0741003642 388 ‑0.3168278913 602 ‑0.0004095121 175 0.0747452558 389 ‑0.3059098575 603 ‑0.0004606325 176 0.0753137336 390 ‑0.2950716717 604 ‑0.0005145572 177 0.0758008358 391 ‑0.2843214189 605 ‑0.0005564576 178 0.0761992479 392 ‑0.2736634040 606 ‑0.0005946118 179 0.0764992170 393 ‑0.2631053299 607 ‑0.0006341594 180 0.0767093490 394 ‑0.2526480309 608 ‑0.0006650415 181 0.0768173975 395 ‑0.2423016884 609 ‑0.0006917937 182 0.0768230011 396 ‑0.2320690870 610 ‑0.0007215391 183 0.0767204924 397 ‑0.2219652696 611 ‑0.0007319357 184 0.0765050718 398 ‑0.2119735853 612 ‑0.0007530001 185 0.0761748321 399 ‑0.2021250176 613 ‑0.0007630793 186 0.0757305756 400 ‑0.1923966745 614 ‑0.0007757977 28 EP 4 756 801 A1 5 10 15 20 25 30 35 40 45 50 55 (continued) n p0(n) n p0(n) n p0(n) 187 0.0751576255 401 ‑0.1828172548 615 ‑0.0007801449 188 0.0744664394 402 ‑0.1733808172 616 ‑0.0007803664 189 0.0736406005 403 ‑0.1640958855 617 ‑0.0007779869 190 0.0726774642 404 ‑0.1549607071 618 ‑0.0007834332 191 0.0715826364 405 ‑0.1459766491 619 ‑0.0007724848 192 0.0703533073 406 ‑0.1371551761 620 ‑0.0007681371 193 0.0689664013 407 ‑0.1285002850 621 ‑0.0007490598 194 0.0674525021 408 ‑0.1200077984 622 ‑0.0007440941 195 0.0657690668 409 ‑0.1116826931 623 ‑0.0007255043 196 0.0639444805 410 ‑0.1035329531 624 ‑0.0007157736 197 0.0619602779 411 ‑0.0955533352 625 ‑0.0006941614 198 0.0598166570 412 ‑0.0877547536 626 ‑0.0006777690 199 0.0575152691 413 ‑0.0801372934 627 ‑0.0006540333 200 0.0550460034 414 ‑0.0726943300 628 ‑0.0006312493 201 0.0524093821 415 ‑0.0654409853 629 ‑0.0006132747 202 0.0495978676 416 ‑0.0583705326 630 ‑0.0005870930 203 0.0466303305 417 ‑0.0514804176 631 ‑0.0005677802 204 0.0434768782 418 ‑0.0447806821 632 ‑0.0005466565 205 0.0401458278 419 ‑0.0382776572 633 ‑0.0005226564 206 0.0366418116 420 ‑0.0319531274 634 ‑0.0005040714 207 0.0329583930 421 ‑0.0258227288 635 ‑0.0004893791 208 0.0290824006 422 ‑0.0198834129 636 ‑0.0004875227 209 0.0250307561 423 ‑0.0141288827 637 ‑0.0004947518 210 0.0207997072 424 ‑0.0085711749 638 ‑0.0005617692 211 0.0163701258 425 ‑0.0032086896 639 ‑0.0005525280 212 0.0117623832 426 0.0019765601 213 0.0069636862 427 0.0069636862 2. A computer program having instructions that when executed by a processor cause said processor to perform the method of claim 1. 3. A decoder for decoding an encoded audio bitstream, the decoder comprising: an input interface for receiving the encoded audio bitstream, the encoded audio bitstream including audio data representing a lowband portion of an audio signal; a core decoder for decoding the audio data to generate a decoded lowband audio signal; a deformatter for extracting from the encoded audio bitstream high frequency reconstruction metadata, the high frequency reconstruction metadata including operating parameters for a high frequency reconstruction process that linearly translates a consecutive number of subbands from a lowband portion of the audio signal to a highband portion of the audio signal; an analysis filterbank for filtering the decoded lowband audio signal to generate a filtered lowband audio signal; a deformatter for extracting from the encoded audio bitstreama flag indicatingwhether either linear translation or harmonic transposition is to be performed on the audio data; the decoder being configured for extracting from the encoded audio bitstream a parameter indicating whether to 29 EP 4 756 801 A1 5 10 15 20 25 30 35 40 45 50 55 use signal adaptive frequency domain oversampling; wherein the encoded audio bitstream further includes a fill element with an identifier indicating a start of the fill element and fill data after the identifier, wherein the fill data includes the flag; wherein the fill data includes an extension payload, the extension payload includes spectral band replication extensiondata, and theextensionpayload is identifiedwitha four bit unsigned integer transmittedmost significant bit first and having a value of ’1101’ or ’1110’, wherein the identifier is a three bit unsigned integer transmittedmost significant bit first and having a value of 0x6; wherein the spectral band replication extension data includes: a high frequency regenerator for regenerating a highband portion of the audio signal by performing harmonic transposition using the filtered lowband audio signal and the high frequency reconstruction metadata, if the flag indicates that harmonic transposition is to be performed on the audio data; and a synthesis filterbank for combining the filtered lowband audio signal and the regenerated highband portion to form a wideband audio signal, wherein a phase shift is added to the filtered lowband audio signal after the filtering and compensated for before the combining; and characterized in that the analysis filterbank includes analysis filters, hk(n), that are modulated versions of a prototype filter, p0(n), according to: where p0(n) is a real-valued symmetric or asymmetric prototype filter, M is a number of channels in the analysis filterbank andN is the prototype filter order; wherein the prototype filter, p0(n), is defined by the coefficients of the following Table: n p0(n) n p0(n) n p0(n) 0 0.0000000000 214 0.0019765601 428 0.0117623832 1 ‑0.0005525286 215 ‑0.0032086896 429 0.0163701258 2 ‑0.0005617692 216 ‑0.0085711749 430 0.0207997072 3 ‑0.0004947518 217 ‑0.0141288827 431 0.0250307561 4 ‑0.0004875227 218 ‑0.0198834129 432 0.0290824006 5 ‑0.0004893791 219 ‑0.0258227288 433 0.0329583930 6 ‑0.0005040714 220 ‑0.0319531274 434 0.0366418116 7 ‑0.0005226564 221 ‑0.0382776572 435 0.0401458278 8 ‑0.0005466565 222 ‑0.0447806821 436 0.0434768782 9 ‑0.0005677802 223 ‑0.0514804176 437 0.0466303305 10 ‑0.0005870930 224 ‑0.0583705326 438 0.0495978676 11 ‑0.0006132747 225 ‑0.0654409853 439 0.0524093821 12 ‑0.0006312493 226 ‑0.0726943300 440 0.0550460034 13 ‑0.0006540333 227 ‑0.0801372934 441 0.0575152691 14 ‑0.0006777690 228 ‑0.0877547536 442 0.0598166570 15 ‑0.0006941614 229 ‑0.0955533352 443 0.0619602779 16 ‑0.0007157736 230 ‑0.1035329531 444 0.0639444805 17 ‑0.0007255043 231 ‑0.1116826931 445 0.0657690668 18 ‑0.0007440941 232 ‑0.1200077984 446 0.0674525021 19 ‑0.0007490598 233 ‑0.1285002850 447 0.0689664013 20 ‑0.0007681371 234 ‑0.1371551761 448 0.0703533073 30 EP 4 756 801 A1 5 10 15 20 25 30 35 40 45 50 55 (continued) n p0(n) n p0(n) n p0(n) 21 ‑0.0007724848 235 ‑0.1459766491 449 0.0715826364 22 ‑0.0007834332 236 ‑0.1549607071 450 0.0726774642 23 ‑0.0007779869 237 ‑0.1640958855 451 0.0736406005 24 ‑0.0007803664 238 ‑0.1733808172 452 0.0744664394 25 ‑0.0007801449 239 ‑0.1828172548 453 0.0751576255 26 ‑0.0007757977 240 ‑0.1923966745 454 0.0757305756 27 ‑0.0007630793 241 ‑0.2021250176 455 0.0761748321 28 ‑0.0007530001 242 ‑0.2119735853 456 0.0765050718 29 ‑0.0007319357 243 ‑0.2219652696 457 0.0767204924 30 ‑0.0007215391 244 ‑0.2320690870 458 0.0768230011 31 ‑0.0006917937 245 ‑0.2423016884 459 0.0768173975 32 ‑0.0006650415 246 ‑0.2526480309 460 0.0767093490 33 ‑0.0006341594 247 ‑0.2631053299 461 0.0764992170 34 ‑0.0005946118 248 ‑0.2736634040 462 0.0761992479 35 ‑0.0005564576 249 ‑0.2843214189 463 0.0758008358 36 ‑0.0005145572 250 ‑0.2950716717 464 0.0753137336 37 ‑0.0004606325 251 ‑0.3059098575 465 0.0747452558 38 ‑0.0004095121 252 ‑0.3168278913 466 0.0741003642 39 ‑0.0003501175 253 ‑0.3278113727 467 0.0733620255 40 ‑0.0002896981 254 ‑0.3388722693 468 0.0725682583 41 ‑0.0002098337 255 ‑0.3499914122 469 0.0717002673 42 ‑0.0001446380 256 0.3611589903 470 0.0707628710 43 ‑0.0000617334 257 0.3723795546 471 0.0697630244 44 0.0000134949 258 0.3836350013 472 0.0687043828 45 0.0001094383 259 0.3949211761 473 0.0676075985 46 0.0002043017 260 0.4062317676 474 0.0664367512 47 0.0002949531 261 0.4175696896 475 0.0652247106 48 0.0004026540 262 0.4289119920 476 0.0639715898 49 0.0005107388 263 0.4402553754 477 0.0626857808 50 0.0006239376 264 0.4515996535 478 0.0613455171 51 0.0007458025 265 0.4629308085 479 0.0599837480 52 0.0008608443 266 0.4742453214 480 0.0585915683 53 0.0009885988 267 0.4855253091 481 0.0571616450 54 0.0011250155 268 0.4967708254 482 0.0557173648 55 0.0012577884 269 0.5079817500 483 0.0542452768 56 0.0013902494 270 0.5191234970 484 0.0527630746 57 0.0015443219 271 0.5302240895 485 0.0512556155 58 0.0016868083 272 0.5412553448 486 0.0497385755 59 0.0018348265 273 0.5522051258 487 0.0482165720 31 EP 4 756 801 A1 5 10 15 20 25 30 35 40 45 50 55 (continued) n p0(n) n p0(n) n p0(n) 60 0.0019841140 274 0.5630789140 488 0.0466843027 61 0.0021461583 275 0.5738524131 489 0.0451488405 62 0.0023017254 276 0.5845403235 490 0.0436097542 63 0.0024625616 277 0.5951123086 491 0.0420649094 64 0.0026201758 278 0.6055783538 492 0.0405349170 65 0.0027870464 279 0.6159109932 493 0.0390053679 66 0.0029469447 280 0.6261242695 494 0.0374812850 67 0.0031125420 281 0.6361980107 495 0.0359697560 68 0.0032739613 282 0.6461269695 496 0.0344620948 69 0.0034418874 283 0.6559016302 497 0.0329754081 70 0.0036008268 284 0.6655139880 498 0.0315017608 71 0.0037603922 285 0.6749663190 499 0.0300502657 72 0.0039207432 286 0.6842353293 500 0.0286072173 73 0.0040819753 287 0.6933282376 501 0.0271859429 74 0.0042264269 288 0.7022388719 502 0.0257875847 75 0.0043730719 289 0.7109410426 503 0.0244160992 76 0.0045209852 290 0.7194462634 504 0.0230680169 77 0.0046606460 291 0.7277448900 505 0.0217467550 78 0.0047932560 292 0.7358211758 506 0.0204531793 79 0.0049137603 293 0.7436827863 507 0.0191872431 80 0.0050393022 294 0.7513137456 508 0.0179433381 81 0.0051407353 295 0.7587080760 509 0.0167324712 82 0.0052461166 296 0.7658674865 510 0.0155405553 83 0.0053471681 297 0.7727780881 511 0.0143904666 84 0.0054196775 298 0.7794287519 512 ‑0.0132718220 85 0.0054876040 299 0.7858353120 513 ‑0.0121849995 86 0.0055475714 300 0.7919735841 514 ‑0.0111315548 87 0.0055938023 301 0.7978466413 515 ‑0.0101150215 88 0.0056220643 302 0.8034485751 516 ‑0.0091325329 89 0.0056455196 303 0.8087695004 517 ‑0.0081798233 90 0.0056389199 304 0.8138191270 518 ‑0.0072615816 91 0.0056266114 305 0.8185776004 519 ‑0.0063792293 92 0.0055917128 306 0.8230419890 520 ‑0.0055337211 93 0.0055404363 307 0.8272275347 521 ‑0.0047222596 94 0.0054753783 308 0.8311038457 522 ‑0.0039401124 95 0.0053838975 309 0.8346937361 523 ‑0.0031933778 96 0.0052715758 310 0.8379717337 524 ‑0.0024826723 97 0.0051382275 311 0.8409541392 525 ‑0.0018039472 98 0.0049839687 312 0.8436238281 526 ‑0.0011568135 32 EP 4 756 801 A1 5 10 15 20 25 30 35 40 45 50 55 (continued) n p0(n) n p0(n) n p0(n) 99 0.0048109469 313 0.8459818469 527 ‑0.0005464280 100 0.0046039530 314 0.8480315777 528 0.0000276045 101 0.0043801861 315 0.8497805198 529 0.0005832264 102 0.0041251642 316 0.8511971524 530 0.0010902329 103 0.0038456408 317 0.8523047035 531 0.0015784682 104 0.0035401246 318 0.8531020949 532 0.0020274176 105 0.0032091885 319 0.8535720573 533 0.0024508540 106 0.0028446757 320 0.8537385600 534 0.0028446757 107 0.0024508540 321 0.8535720573 535 0.0032091885 108 0.0020274176 322 0.8531020949 536 0.0035401246 109 0.0015784682 323 0.8523047035 537 0.0038456408 110 0.0010902329 324 0.8511971524 538 0.0041251642 111 0.0005832264 325 0.8497805198 539 0.0043801861 112 0.0000276045 326 0.8480315777 540 0.0046039530 113 ‑0.0005464280 327 0.8459818469 541 0.0048109469 114 ‑0.0011568135 328 0.8436238281 542 0.0049839687 115 ‑0.0018039472 329 0.8409541392 543 0.0051382275 116 ‑0.0024826723 330 0.8379717337 544 0.0052715758 117 ‑0.0031933778 331 0.8346937361 545 0.0053838975 118 ‑0.0039401124 332 0.8311038457 546 0.0054753783 119 ‑0.0047222596 333 0.8272275347 547 0.0055404363 120 ‑0.0055337211 334 0.8230419890 548 0.0055917128 121 ‑0.0063792293 335 0.8185776004 549 0.0056266114 122 ‑0.0072615816 336 0.8138191270 550 0.0056389199 123 ‑0.0081798233 337 0.8087695004 551 0.0056455196 124 ‑0.0091325329 338 0.8034485751 552 0.0056220643 125 ‑0.0101150215 339 0.7978466413 553 0.0055938023 126 ‑0.0111315548 340 0.7919735841 554 0.0055475714 127 ‑0.0121849995 341 0.7858353120 555 0.0054876040 128 0.0132718220 342 0.7794287519 556 0.0054196775 129 0.0143904666 343 0.7727780881 557 0.0053471681 130 0.0155405553 344 0.7658674865 558 0.0052461166 131 0.0167324712 345 0.7587080760 559 0.0051407353 132 0.0179433381 346 0.7513137456 560 0.0050393022 133 0.0191872431 347 0.7436827863 561 0.0049137603 134 0.0204531793 348 0.7358211758 562 0.0047932560 135 0.0217467550 349 0.7277448900 563 0.0046606460 136 0.0230680169 350 0.7194462634 564 0.0045209852 137 0.0244160992 351 0.7109410426 565 0.0043730719 33 EP 4 756 801 A1 5 10 15 20 25 30 35 40 45 50 55 (continued) n p0(n) n p0(n) n p0(n) 138 0.0257875847 352 0.7022388719 566 0.0042264269 139 0.0271859429 353 0.6933282376 567 0.0040819753 140 0.0286072173 354 0.6842353293 568 0.0039207432 141 0.0300502657 355 0.6749663190 569 0.0037603922 142 0.0315017608 356 0.6655139880 570 0.0036008268 143 0.0329754081 357 0.6559016302 571 0.0034418874 144 0.0344620948 358 0.6461269695 572 0.0032739613 145 0.0359697560 359 0.6361980107 573 0.0031125420 146 0.0374812850 360 0.6261242695 574 0.0029469447 147 0.0390053679 361 0.6159109932 575 0.0027870464 148 0.0405349170 362 0.6055783538 576 0.0026201758 149 0.0420649094 363 0.5951123086 577 0.0024625616 150 0.0436097542 364 0.5845403235 578 0.0023017254 151 0.0451488405 365 0.5738524131 579 0.0021461583 152 0.0466843027 366 0.5630789140 580 0.0019841140 153 0.0482165720 367 0.5522051258 581 0.0018348265 154 0.0497385755 368 0.5412553448 582 0.0016868083 155 0.0512556155 369 0.5302240895 583 0.0015443219 156 0.0527630746 370 0.5191234970 584 0.0013902494 157 0.0542452768 371 0.5079817500 585 0.0012577884 158 0.0557173648 372 0.4967708254 586 0.0011250155 159 0.0571616450 373 0.4855253091 587 0.0009885988 160 0.0585915683 374 0.4742453214 588 0.0008608443 161 0.0599837480 375 0.4629308085 589 0.0007458025 162 0.0613455171 376 0.4515996535 590 0.0006239376 163 0.0626857808 377 0.4402553754 591 0.0005107388 164 0.0639715898 378 0.4289119920 592 0.0004026540 165 0.0652247106 379 0.4175696896 593 0.0002949531 166 0.0664367512 380 0.4062317676 594 0.0002043017 167 0.0676075985 381 0.3949211761 595 0.0001094383 168 0.0687043828 382 0.3836350013 596 0.0000134949 169 0.0697630244 383 0.3723795546 597 ‑0.0000617334 170 0.0707628710 384 ‑0.3611589903 598 ‑0.0001446380 171 0.0717002673 385 ‑0.3499914122 599 ‑0.0002098337 172 0.0725682583 386 ‑0.3388722693 600 ‑0.0002896981 173 0.0733620255 387 ‑0.3278113727 601 ‑0.0003501175 174 0.0741003642 388 ‑0.3168278913 602 ‑0.0004095121 175 0.0747452558 389 ‑0.3059098575 603 ‑0.0004606325 176 0.0753137336 390 ‑0.2950716717 604 ‑0.0005145572 34 EP 4 756 801 A1 5 10 15 20 25 30 35 40 45 50 55 (continued) n p0(n) n p0(n) n p0(n) 177 0.0758008358 391 ‑0.2843214189 605 ‑0.0005564576 178 0.0761992479 392 ‑0.2736634040 606 ‑0.0005946118 179 0.0764992170 393 ‑0.2631053299 607 ‑0.0006341594 180 0.0767093490 394 ‑0.2526480309 608 ‑0.0006650415 181 0.0768173975 395 ‑0.2423016884 609 ‑0.0006917937 182 0.0768230011 396 ‑0.2320690870 610 ‑0.0007215391 183 0.0767204924 397 ‑0.2219652696 611 ‑0.0007319357 184 0.0765050718 398 ‑0.2119735853 612 ‑0.0007530001 185 0.0761748321 399 ‑0.2021250176 613 ‑0.0007630793 186 0.0757305756 400 ‑0.1923966745 614 ‑0.0007757977 187 0.0751576255 401 ‑0.1828172548 615 ‑0.0007801449 188 0.0744664394 402 ‑0.1733808172 616 ‑0.0007803664 189 0.0736406005 403 ‑0.1640958855 617 ‑0.0007779869 190 0.0726774642 404 ‑0.1549607071 618 ‑0.0007834332 191 0.0715826364 405 ‑0.1459766491 619 ‑0.0007724848 192 0.0703533073 406 ‑0.1371551761 620 ‑0.0007681371 193 0.0689664013 407 ‑0.1285002850 621 ‑0.0007490598 194 0.0674525021 408 ‑0.1200077984 622 ‑0.0007440941 195 0.0657690668 409 ‑0.1116826931 623 ‑0.0007255043 196 0.0639444805 410 ‑0.1035329531 624 ‑0.0007157736 197 0.0619602779 411 ‑0.0955533352 625 ‑0.0006941614 198 0.0598166570 412 ‑0.0877547536 626 ‑0.0006777690 199 0.0575152691 413 ‑0.0801372934 627 ‑0.0006540333 200 0.0550460034 414 ‑0.0726943300 628 ‑0.0006312493 201 0.0524093821 415 ‑0.0654409853 629 ‑0.0006132747 202 0.0495978676 416 ‑0.0583705326 630 ‑0.0005870930 203 0.0466303305 417 ‑0.0514804176 631 ‑0.0005677802 204 0.0434768782 418 ‑0.0447806821 632 ‑0.0005466565 205 0.0401458278 419 ‑0.0382776572 633 ‑0.0005226564 206 0.0366418116 420 ‑0.0319531274 634 ‑0.0005040714 207 0.0329583930 421 ‑0.0258227288 635 ‑0.0004893791 208 0.0290824006 422 ‑0.0198834129 636 ‑0.0004875227 209 0.0250307561 423 ‑0.0141288827 637 ‑0.0004947518 210 0.0207997072 424 ‑0.0085711749 638 ‑0.0005617692 211 0.0163701258 425 ‑0.0032086896 639 ‑0.0005525280 212 0.0117623832 426 0.0019765601 213 0.0069636862 427 0.0069636862 35 EP 4 756 801 A1 5 10 15 20 25 30 35 40 45 50 55 36 EP 4 756 801 A1 37 EP 4 756 801 A1 38 EP 4 756 801 A1 5 10 15 20 25 30 35 40 45 50 55 39 EP 4 756 801 A1 5 10 15 20 25 30 35 40 45 50 55 40 EP 4 756 801 A1 5 10 15 20 25 30 35 40 45 50 55 41 EP 4 756 801 A1 5 10 15 20 25 30 35 40 45 50 55 42 EP 4 756 801 A1 5 10 15 20 25 30 35 40 45 50 55 43 EP 4 756 801 A1 5 10 15 20 25 30 35 40 45 50 55 44 EP 4 756 801 A1 REFERENCES CITED IN THE DESCRIPTION This list of references cited by the applicant is for the reader’s convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard. Patent documents cited in the description • EP 25210522

[0001] 用于音频信号的高频重建的谐波转置器的后向兼容集成 摘要 本申请揭示一种用于解码经编码音频位流的方法。所述方法包含接收所述经编码 音频位流，及解码音频数据以产生经解码低带音频信号。所述方法进一步包含提 取高频重建元数据，及使用分析滤波器组对所述经解码低带音频信号进行滤波以 产生经滤波低带音频信号。所述方法还包含提取指示将对所述音频数据执行频谱 变换还是谐波转置的旗标，及根据所述旗标使用所述经滤波低带音频信号及所述 高频重建元数据再生所述音频信号的高带部分。 摘要

Claims

1. A method for decoding an encoded audio bitstream, the method comprising: receiving the encoded audio bitstream, the encoded audio bitstream including audio data representing a lowband portion of an audio signal; decoding the audio data to generate a decoded lowband audio signal; extracting from the encoded audio bitstream high frequency reconstruction metadata, the high frequency reconstruction metadata including operating parameters for a high frequency reconstruction process that linearly translates a consecutive number of subbands from a lowband portion of the audio signal to a highband portion of the audio signal; filtering the decoded lowband audio signal with an analysis filterbank to generate a filtered lowband audio signal; extracting from the encoded audio bitstream a flag indicating whether either linear translation or harmonic transposition is to be performed on the audio data; extracting from the encoded audio bitstream a parameter indicating whether to use signal adaptive frequency domain oversampling; wherein the encoded audio bitstream further includes a fill element with an identifier indicating a start of the fill element and fill data after the identifier, wherein the fill data includes the flag; wherein the fill data includes an extension payload, the extension payload includes spectral band replication extension data, and the extension payload is identified with a four bit unsigned integer transmitted most significant bit first and having a value of '1101' or '1110', wherein the identifier is a three bit unsigned integer transmitted most significant bit first and having a value of 0x6; if the flag indicates that harmonic transposition is to be performed on the audio data: regenerating a highband portion of the audio signal by performing harmonic transposition using the filtered lowband audio signal and the high frequency reconstruction metadata; and combining the filtered lowband audio signal and the regenerated highband portion to form a wideband audio signal, wherein a phase shift is added to the filtered lowband audio signal after the filtering and compensated for before the combining, characterized in that the analysis filterbank includes analysis filters, hk(n), that are modulated versions of a prototype filter, p0(n), according to: h k n = p 0 n exp i π M k + 1 2 n − N 2 , 0 ≤ n ≤ N ; 0 ≤ k < M where p0(n) is a real-valued symmetric or asymmetric prototype filter, M is a number of channels in the analysis filterbank and N is the prototype filter order; wherein the prototype filter, p0(n), is defined by the coefficients of the following Table: np0(n)np0(n)np0(n)00.00000000002140.00197656014280.01176238321-0.0005525286215-0.00320868964290.01637012582-0.0005617692216-0.00857117494300.02079970723-0.0004947518217-0.01412888274310.02503075614-0.0004875227218-0.01988341294320.02908240065-0.0004893791219-0.02582272884330.03295839306-0.0005040714220-0.03195312744340.03664181167-0.0005226564221-0.03827765724350.04014582788-0.0005466565222-0.04478068214360.04347687829-0.0005677802223-0.05148041764370.046630330510-0.0005870930224-0.05837053264380.049597867611-0.0006132747225-0.06544098534390.052409382112-0.0006312493226-0.07269433004400.055046003413-0.0006540333227-0.08013729344410.057515269114-0.0006777690228-0.08775475364420.059816657015-0.0006941614229-0.09555333524430.061960277916-0.0007157736230-0.10353295314440.063944480517-0.0007255043231-0.11168269314450.065769066818-0.0007440941232-0.12000779844460.067452502119-0.0007490598233-0.12850028504470.068966401320-0.0007681371234-0.13715517614480.070353307321-0.0007724848235-0.14597664914490.071582636422-0.0007834332236-0.15496070714500.072677464223-0.0007779869237-0.16409588554510.073640600524-0.0007803664238-0.17338081724520.074466439425-0.0007801449239-0.18281725484530.075157625526-0.0007757977240-0.19239667454540.075730575627-0.0007630793241-0.20212501764550.076174832128-0.0007530001242-0.21197358534560.076505071829-0.0007319357243-0.22196526964570.076720492430-0.0007215391244-0.23206908704580.076823001131-0.0006917937245-0.24230168844590.076817397532-0.0006650415246-0.25264803094600.076709349033-0.0006341594247-0.26310532994610.076499217034-0.0005946118248-0.27366340404620.076199247935-0.0005564576249-0.28432141894630.075800835836-0.0005145572250-0.29507167174640.075313733637-0.0004606325251-0.30590985754650.074745255838-0.0004095121252-0.31682789134660.074100364239-0.0003501175253-0.32781137274670.073362025540-0.0002896981254-0.33887226934680.072568258341-0.0002098337255-0.34999141224690.071700267342-0.00014463802560.36115899034700.070762871043-0.00006173342570.37237955464710.0697630244440.00001349492580.38363500134720.0687043828450.00010943832590.39492117614730.0676075985460.00020430172600.40623176764740.0664367512470.00029495312610.41756968964750.0652247106480.00040265402620.42891199204760.0639715898490.00051073882630.44025537544770.0626857808500.00062393762640.45159965354780.0613455171510.00074580252650.46293080854790.0599837480520.00086084432660.47424532144800.0585915683530.00098859882670.48552530914810.0571616450540.00112501552680.49677082544820.0557173648550.00125778842690.50798175004830.0542452768560.00139024942700.51912349704840.0527630746570.00154432192710.53022408954850.0512556155580.00168680832720.54125534484860.0497385755590.00183482652730.55220512584870.0482165720600.00198411402740.56307891404880.0466843027610.00214615832750.57385241314890.0451488405620.00230172542760.58454032354900.0436097542630.00246256162770.59511230864910.0420649094640.00262017582780.60557835384920.0405349170650.00278704642790.61591099324930.0390053679660.00294694472800.62612426954940.0374812850670.00311254202810.63619801074950.0359697560680.00327396132820.64612696954960.0344620948690.00344188742830.65590163024970.0329754081700.00360082682840.66551398804980.0315017608710.00376039222850.67496631904990.0300502657720.00392074322860.68423532935000.0286072173730.00408197532870.69332823765010.0271859429740.00422642692880.70223887195020.0257875847750.00437307192890.71094104265030.0244160992760.00452098522900.71944626345040.0230680169770.00466064602910.72774489005050.0217467550780.00479325602920.73582117585060.0204531793790.00491376032930.74368278635070.0191872431800.00503930222940.75131374565080.0179433381810.00514073532950.75870807605090.0167324712820.00524611662960.76586748655100.0155405553830.00534716812970.77277808815110.0143904666840.00541967752980.7794287519512-0.0132718220850.00548760402990.7858353120513-0.0121849995860.00554757143000.7919735841514-0.0111315548870.00559380233010.7978466413515-0.0101150215880.00562206433020.8034485751516-0.0091325329890.00564551963030.8087695004517-0.0081798233900.00563891993040.8138191270518-0.0072615816910.00562661143050.8185776004519-0.0063792293920.00559171283060.8230419890520-0.0055337211930.00554043633070.8272275347521-0.0047222596940.00547537833080.8311038457522-0.0039401124950.00538389753090.8346937361523-0.0031933778960.00527157583100.8379717337524-0.0024826723970.00513822753110.8409541392525-0.0018039472980.00498396873120.8436238281526-0.0011568135990.00481094693130.8459818469527-0.00054642801000.00460395303140.84803157775280.00002760451010.00438018613150.84978051985290.00058322641020.00412516423160.85119715245300.00109023291030.00384564083170.85230470355310.00157846821040.00354012463180.85310209495320.00202741761050.00320918853190.85357205735330.00245085401060.00284467573200.85373856005340.00284467571070.00245085403210.85357205735350.00320918851080.00202741763220.85310209495360.00354012461090.00157846823230.85230470355370.00384564081100.00109023293240.85119715245380.00412516421110.00058322643250.84978051985390.00438018611120.00002760453260.84803157775400.0046039530113-0.00054642803270.84598184695410.0048109469114-0.00115681353280.84362382815420.0049839687115-0.00180394723290.84095413925430.0051382275116-0.00248267233300.83797173375440.0052715758117-0.00319337783310.83469373615450.0053838975118-0.00394011243320.83110384575460.0054753783119-0.00472225963330.82722753475470.0055404363120-0.00553372113340.82304198905480.0055917128121-0.00637922933350.81857760045490.0056266114122-0.00726158163360.81381912705500.0056389199123-0.00817982333370.80876950045510.0056455196124-0.00913253293380.80344857515520.0056220643125-0.01011502153390.79784664135530.0055938023126-0.01113155483400.79197358415540.0055475714127-0.01218499953410.78583531205550.00548760401280.01327182203420.77942875195560.00541967751290.01439046663430.77277808815570.00534716811300.01554055533440.76586748655580.00524611661310.01673247123450.75870807605590.00514073531320.01794333813460.75131374565600.00503930221330.01918724313470.74368278635610.00491376031340.02045317933480.73582117585620.00479325601350.02174675503490.72774489005630.00466064601360.02306801693500.71944626345640.00452098521370.02441609923510.71094104265650.00437307191380.02578758473520.70223887195660.00422642691390.02718594293530.69332823765670.00408197531400.02860721733540.68423532935680.00392074321410.03005026573550.67496631905690.00376039221420.03150176083560.66551398805700.00360082681430.03297540813570.65590163025710.00344188741440.03446209483580.64612696955720.00327396131450.03596975603590.63619801075730.00311254201460.03748128503600.62612426955740.00294694471470.03900536793610.61591099325750.00278704641480.04053491703620.60557835385760.00262017581490.04206490943630.59511230865770.00246256161500.04360975423640.58454032355780.00230172541510.04514884053650.57385241315790.00214615831520.04668430273660.56307891405800.00198411401530.04821657203670.55220512585810.00183482651540.04973857553680.54125534485820.00168680831550.05125561553690.53022408955830.00154432191560.05276307463700.51912349705840.00139024941570.05424527683710.50798175005850.00125778841580.05571736483720.49677082545860.00112501551590.05716164503730.48552530915870.00098859881600.05859156833740.47424532145880.00086084431610.05998374803750.46293080855890.00074580251620.06134551713760.45159965355900.00062393761630.06268578083770.44025537545910.00051073881640.06397158983780.42891199205920.00040265401650.06522471063790.41756968965930.00029495311660.06643675123800.40623176765940.00020430171670.06760759853810.39492117615950.00010943831680.06870438283820.38363500135960.00001349491690.06976302443830.3723795546597-0.00006173341700.0707628710384-0.3611589903598-0.00014463801710.0717002673385-0.3499914122599-0.00020983371720.0725682583386-0.3388722693600-0.00028969811730.0733620255387-0.3278113727601-0.00035011751740.0741003642388-0.3168278913602-0.00040951211750.0747452558389-0.3059098575603-0.00046063251760.0753137336390-0.2950716717604-0.00051455721770.0758008358391-0.2843214189605-0.00055645761780.0761992479392-0.2736634040606-0.00059461181790.0764992170393-0.2631053299607-0.00063415941800.0767093490394-0.2526480309608-0.00066504151810.0768173975395-0.2423016884609-0.00069179371820.0768230011396-0.2320690870610-0.00072153911830.0767204924397-0.2219652696611-0.00073193571840.0765050718398-0.2119735853612-0.00075300011850.0761748321399-0.2021250176613-0.00076307931860.0757305756400-0.1923966745614-0.00077579771870.0751576255401-0.1828172548615-0.00078014491880.0744664394402-0.1733808172616-0.00078036641890.0736406005403-0.1640958855617-0.00077798691900.0726774642404-0.1549607071618-0.00078343321910.0715826364405-0.1459766491619-0.00077248481920.0703533073406-0.1371551761620-0.00076813711930.0689664013407-0.1285002850621-0.00074905981940.0674525021408-0.1200077984622-0.00074409411950.0657690668409-0.1116826931623-0.00072550431960.0639444805410-0.1035329531624-0.00071577361970.0619602779411-0.0955533352625-0.00069416141980.0598166570412-0.0877547536626-0.00067776901990.0575152691413-0.0801372934627-0.00065403332000.0550460034414-0.0726943300628-0.00063124932010.0524093821415-0.0654409853629-0.00061327472020.0495978676416-0.0583705326630-0.00058709302030.0466303305417-0.0514804176631-0.00056778022040.0434768782418-0.0447806821632-0.00054665652050.0401458278419-0.0382776572633-0.00052265642060.0366418116420-0.0319531274634-0.00050407142070.0329583930421-0.0258227288635-0.00048937912080.0290824006422-0.0198834129636-0.00048752272090.0250307561423-0.0141288827637-0.00049475182100.0207997072424-0.0085711749638-0.00056176922110.0163701258425-0.0032086896639-0.00055252802120.01176238324260.00197656012130.00696368624270.00696368622. A computer program having instructions that when executed by a processor cause said processor to perform the method of claim 1.

3. A decoder for decoding an encoded audio bitstream, the decoder comprising: an input interface for receiving the encoded audio bitstream, the encoded audio bitstream including audio data representing a lowband portion of an audio signal; a core decoder for decoding the audio data to generate a decoded lowband audio signal; a deformatter for extracting from the encoded audio bitstream high frequency reconstruction metadata, the high frequency reconstruction metadata including operating parameters for a high frequency reconstruction process that linearly translates a consecutive number of subbands from a lowband portion of the audio signal to a highband portion of the audio signal; an analysis filterbank for filtering the decoded lowband audio signal to generate a filtered lowband audio signal; a deformatter for extracting from the encoded audio bitstream a flag indicating whether either linear translation or harmonic transposition is to be performed on the audio data; the decoder being configured for extracting from the encoded audio bitstream a parameter indicating whether to use signal adaptive frequency domain oversampling; wherein the encoded audio bitstream further includes a fill element with an identifier indicating a start of the fill element and fill data after the identifier, wherein the fill data includes the flag; wherein the fill data includes an extension payload, the extension payload includes spectral band replication extension data, and the extension payload is identified with a four bit unsigned integer transmitted most significant bit first and having a value of '1101' or '1110', wherein the identifier is a three bit unsigned integer transmitted most significant bit first and having a value of 0x6; wherein the spectral band replication extension data includes: a high frequency regenerator for regenerating a highband portion of the audio signal by performing harmonic transposition using the filtered lowband audio signal and the high frequency reconstruction metadata, if the flag indicates that harmonic transposition is to be performed on the audio data; and a synthesis filterbank for combining the filtered lowband audio signal and the regenerated highband portion to form a wideband audio signal, wherein a phase shift is added to the filtered lowband audio signal after the filtering and compensated for before the combining; and characterized in that the analysis filterbank includes analysis filters, hk(n), that are modulated versions of a prototype filter, p0(n), according to: h k n = p 0 n exp i π M k + 1 2 n − N 2 , 0 ≤ n ≤ N ; 0 ≤ k < M where p0(n) is a real-valued symmetric or asymmetric prototype filter, M is a number of channels in the analysis filterbank and N is the prototype filter order; wherein the prototype filter, p0(n), is defined by the coefficients of the following Table: np0(n)np0(n)np0(n)00.00000000002140.00197656014280.01176238321-0.0005525286215-0.00320868964290.01637012582-0.0005617692216-0.00857117494300.02079970723-0.0004947518217-0.01412888274310.02503075614-0.0004875227218-0.01988341294320.02908240065-0.0004893791219-0.02582272884330.03295839306-0.0005040714220-0.03195312744340.03664181167-0.0005226564221-0.03827765724350.04014582788-0.0005466565222-0.04478068214360.04347687829-0.0005677802223-0.05148041764370.046630330510-0.0005870930224-0.05837053264380.049597867611-0.0006132747225-0.06544098534390.052409382112-0.0006312493226-0.07269433004400.055046003413-0.0006540333227-0.08013729344410.057515269114-0.0006777690228-0.08775475364420.059816657015-0.0006941614229-0.09555333524430.061960277916-0.0007157736230-0.10353295314440.063944480517-0.0007255043231-0.11168269314450.065769066818-0.0007440941232-0.12000779844460.067452502119-0.0007490598233-0.12850028504470.068966401320-0.0007681371234-0.13715517614480.070353307321-0.0007724848235-0.14597664914490.071582636422-0.0007834332236-0.15496070714500.072677464223-0.0007779869237-0.16409588554510.073640600524-0.0007803664238-0.17338081724520.074466439425-0.0007801449239-0.18281725484530.075157625526-0.0007757977240-0.19239667454540.075730575627-0.0007630793241-0.20212501764550.076174832128-0.0007530001242-0.21197358534560.076505071829-0.0007319357243-0.22196526964570.076720492430-0.0007215391244-0.23206908704580.076823001131-0.0006917937245-0.24230168844590.076817397532-0.0006650415246-0.25264803094600.076709349033-0.0006341594247-0.26310532994610.076499217034-0.0005946118248-0.27366340404620.076199247935-0.0005564576249-0.28432141894630.075800835836-0.0005145572250-0.29507167174640.075313733637-0.0004606325251-0.30590985754650.074745255838-0.0004095121252-0.31682789134660.074100364239-0.0003501175253-0.32781137274670.073362025540-0.0002896981254-0.33887226934680.072568258341-0.0002098337255-0.34999141224690.071700267342-0.00014463802560.36115899034700.070762871043-0.00006173342570.37237955464710.0697630244440.00001349492580.38363500134720.0687043828450.00010943832590.39492117614730.0676075985460.00020430172600.40623176764740.0664367512470.00029495312610.41756968964750.0652247106480.00040265402620.42891199204760.0639715898490.00051073882630.44025537544770.0626857808500.00062393762640.45159965354780.0613455171510.00074580252650.46293080854790.0599837480520.00086084432660.47424532144800.0585915683530.00098859882670.48552530914810.0571616450540.00112501552680.49677082544820.0557173648550.00125778842690.50798175004830.0542452768560.00139024942700.51912349704840.0527630746570.00154432192710.53022408954850.0512556155580.00168680832720.54125534484860.0497385755590.00183482652730.55220512584870.0482165720600.00198411402740.56307891404880.0466843027610.00214615832750.57385241314890.0451488405620.00230172542760.58454032354900.0436097542630.00246256162770.59511230864910.0420649094640.00262017582780.60557835384920.0405349170650.00278704642790.61591099324930.0390053679660.00294694472800.62612426954940.0374812850670.00311254202810.63619801074950.0359697560680.00327396132820.64612696954960.0344620948690.00344188742830.65590163024970.0329754081700.00360082682840.66551398804980.0315017608710.00376039222850.67496631904990.0300502657720.00392074322860.68423532935000.0286072173730.00408197532870.69332823765010.0271859429740.00422642692880.70223887195020.0257875847750.00437307192890.71094104265030.0244160992760.00452098522900.71944626345040.0230680169770.00466064602910.72774489005050.0217467550780.00479325602920.73582117585060.0204531793790.00491376032930.74368278635070.0191872431800.00503930222940.75131374565080.0179433381810.00514073532950.75870807605090.0167324712820.00524611662960.76586748655100.0155405553830.00534716812970.77277808815110.0143904666840.00541967752980.7794287519512-0.0132718220850.00548760402990.7858353120513-0.0121849995860.00554757143000.7919735841514-0.0111315548870.00559380233010.7978466413515-0.0101150215880.00562206433020.8034485751516-0.0091325329890.00564551963030.8087695004517-0.0081798233900.00563891993040.8138191270518-0.0072615816910.00562661143050.8185776004519-0.0063792293920.00559171283060.8230419890520-0.0055337211930.00554043633070.8272275347521-0.0047222596940.00547537833080.8311038457522-0.0039401124950.00538389753090.8346937361523-0.0031933778960.00527157583100.8379717337524-0.0024826723970.00513822753110.8409541392525-0.0018039472980.00498396873120.8436238281526-0.0011568135990.00481094693130.8459818469527-0.00054642801000.00460395303140.84803157775280.00002760451010.00438018613150.84978051985290.00058322641020.00412516423160.85119715245300.00109023291030.00384564083170.85230470355310.00157846821040.00354012463180.85310209495320.00202741761050.00320918853190.85357205735330.00245085401060.00284467573200.85373856005340.00284467571070.00245085403210.85357205735350.00320918851080.00202741763220.85310209495360.00354012461090.00157846823230.85230470355370.00384564081100.00109023293240.85119715245380.0041251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