Decoding method, decoder, medium, and encoding method for interleaved waveform coding

Abstract

To provide methods and apparatuses for decoding and encoding of audio signals.SOLUTION: In particular, a method for decoding includes receiving a waveform-coded signal having a spectral content corresponding to a certain subset of a frequency range above a cross-over frequency. The waveform-coded signal is interleaved with a parametric high frequency reconstruction of the audio signal above the cross-over frequency. In this way, an improved reconstruction of the high frequency bands of the audio signal is achieved.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The invention disclosed herein relates generally to audio encoding and decoding, and more particularly to audio encoders and decoders adapted to perform high frequency reconstruction of audio signals. [Background technology]

[0002] Audio coding systems use different methodologies for coding audio, such as pure waveform coding, parametric spatial coding and high-frequency reconstruction algorithms, including the Spectral Band Replication (SBR) algorithm. The MPEG-4 standard combines waveform coding and SBR of an audio signal. More precisely, an encoder may waveform code the audio signal for the spectral band up to the crossover frequency and encode the spectral band above the crossover frequency using SBR encoding. The waveform-coded part of the audio signal is then transmitted to a decoder together with the SBR parameters determined during the SBR encoding. Then, based on the waveform-coded part of the audio signal and the SBR parameters, the decoder reconstructs the audio signal in the spectral band above the crossover frequency. This is discussed in the review paper "Analyzing the Audio Signal in a Multi-Speed ​​Audio Codec", Vol. 1, No. 1, pp. 1171-1175, 2003.

[0003] One problem with this approach is that strong tonal components, ie strong harmonic components or any components in the high spectral band that are not well reconstructed by the SBR algorithm, are missing in the output.

[0004] To this end, the SBR algorithm implements a missing harmonics detection procedure: tonal components that cannot be properly reconstructed by the SBR high-frequency reconstruction are identified on the encoder side. Information about the frequency location of these strong tonal components is transmitted to the decoder, where the spectral content of the spectral band where the missing tonal components are located is replaced by a decoder-generated sinusoid. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] Brinker et al., "An overview of the Coding Standard MPEG-4 Audio Amendments 1 and 2: HE-AAC, SSC, and HE-AAC v2", EURASIP Journal on Audio, Speech and Music Processing, Volume 2009, Article ID 468971 Summary of the Invention [Problem to be solved by the invention]

[0006] The advantage of the missing harmonic detection provided in the SBR algorithm is that, somewhat simply, it is a very low bit rate solution, since only the frequency location of the tonal components and their amplitude levels need to be transmitted to the decoder. The disadvantage of the missing harmonic detection in the SBR algorithm is that it is a very coarse model. Another disadvantage is that when the transmission rate is low, i.e. when only a small number of bits can be transmitted per second and, as a result, when the spectral band is wide, a large frequency range is replaced by a sine wave.

[0007] Another drawback of the SBR algorithm is that it tends to blur transient components present in the audio signal. Typically, an SBR reconstructed audio signal has pre- and post-echoes of the transient components. Thus, there is room for improvement. [Brief description of the drawings]

[0008] In the following, exemplary embodiments are described in more detail with reference to the accompanying drawings. [Figure 1] FIG. 2 is a schematic diagram of a decoder according to an exemplary embodiment. [Diagram 2] FIG. 2 is a schematic diagram of a decoder according to an exemplary embodiment. [Diagram 3] 4 is a flowchart of a decoding method according to an exemplary embodiment; [Figure 4] FIG. 2 is a schematic diagram of a decoder according to an exemplary embodiment. [Diagram 5] FIG. 2 is a schematic diagram of an encoder according to an example embodiment. [Figure 6] 4 is a flowchart of an encoding method according to an exemplary embodiment. [Figure 7] 1 is a schematic illustration of a signaling scheme according to an exemplary embodiment; [Figure 8] 1A-1B are schematic illustrations of an interleaving stage according to an exemplary embodiment. All drawings are schematic and generally only show parts necessary for clarity of the invention. Other parts may be omitted or only suggested. Unless otherwise stated, like reference signs refer to like parts in different drawings. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] In view of the above, it is an object to provide an encoder and decoder, and associated methods, that provide improved reconstruction of transient and tonal components in high frequency bands.

[0010] I. Overview - Decoder As used herein, an audio signal can be a pure audio signal or an audiovisual signal or the audio part of a multimedia signal or any of these in combination with metadata.

[0011] According to a first aspect, exemplary embodiments propose a decoding method, a decoding device and a computer program product for decoding. The proposed method, device and computer program product may generally have the same features and advantages.

[0012] According to an exemplary embodiment, a decoding method in an audio processing system is provided, the method including: receiving a first waveform-coded signal having spectral content up to a first crossover frequency; receiving a second waveform-coded signal having spectral content corresponding to a subset of a frequency range above the first crossover frequency; receiving high-frequency reconstruction parameters; performing high-frequency reconstruction using the first waveform-coded signal and the high-frequency reconstruction parameters to generate a frequency-extended signal having spectral content above the first crossover frequency; and interleaving the frequency-extended signal with the second waveform-coded signal.

[0013] As used herein, a waveform-coded signal is understood to be a signal that has been coded by direct quantization of a representation of the waveform; most preferably by quantization of lines of a frequency transform of the input waveform signal. This is in contrast to parametric coding, where the signal is represented by a variant of a general model of the signal properties.

[0014] Thus, the decoding method proposes to use waveform-encoded data in a subset of the frequency range above the first crossover frequency and interleave it with the high-frequency reconstructed signal. In this way, important parts of the signal in the frequency band above the first crossover frequency can be waveform-encoded, such as tonal and transient components that are typically not well reconstructed by parametric high-frequency reconstruction algorithms. As a result, the reconstruction of these important parts of the signal in the frequency band above the first crossover frequency is improved.

[0015] According to an exemplary embodiment, the subset of the frequency range above the first crossover frequency is a sparse subset. For example, the subset may consist of a number of isolated frequency intervals. This is advantageous in that the number of bits for coding the second waveform-coded signal is small. Nevertheless, by having a number of isolated frequency intervals, tonal components of the audio signal, e.g. single harmonics, can be well captured by the second waveform-coded signal. As a result, an improved reconstruction of tonal components for high frequency bands is achieved at a low bit cost.

[0016] According to an exemplary embodiment, the second waveform-encoded signal may represent a transient component in the audio signal to be reconstructed. A transient component is typically limited to a short time range, for example about 100 time samples at a sampling rate of 48 kHz, for example a time range of the order of 5 to 10 milliseconds, but may have a wide frequency range. Thus, in order to capture the transient component, the subset of the frequency band above the first crossover frequency may include a frequency interval extending between the first and second crossover frequencies. This is advantageous in that an improved reconstruction of the transient component may be achieved.

[0017] According to an exemplary embodiment, the second crossover frequency varies as a function of time, for example, the second crossover frequency may vary within a time frame set by the audio processing system, in this way short time ranges of transient components may be taken into account.

[0018] According to an exemplary embodiment, performing high frequency reconstruction includes performing Spectral Band Replication (SBR), which is typically performed in the frequency domain, e.g., in the pseudo Quadrature Mirror Filters (QMF) domain, e.g., 64 subbands.

[0019] According to an exemplary embodiment, the step of interleaving the frequency-extended signal with the second waveform-coded signal is performed in the frequency domain, for example the QMF domain. Typically, for simplicity of implementation and better control over the time and frequency characteristics of both signals, the interleaving is performed in the same frequency domain as the high-frequency reconstruction.

[0020] According to an exemplary embodiment, the received first and second waveform-encoded signals are encoded using the same modified discrete cosine transform (MDCT).

[0021] According to an example embodiment, the decoding method may include adjusting the spectral content of the frequency extended signal according to a high-frequency reconstruction parameter, thereby adjusting the spectral envelope of the frequency extended signal.

[0022] According to an exemplary embodiment, interleaving may include adding a second waveform-coded signal to the frequency-extended signal. This is a preferred option when the second waveform-coded signal represents a tonal component, e.g. when said subset of the frequency range above the first crossover frequency includes a number of isolated frequency intervals. Adding a second waveform-coded signal to the frequency-extended signal mimics the parametric addition of harmonics known from SBR and allows the signal copied onto the SBR to be used to avoid large frequency ranges being replaced by a single tonal component by mixing the tonal components at a suitable level.

[0023] According to an exemplary embodiment, the interleaving comprises replacing the spectral content of the frequency-extended signal by the spectral content of the second waveform-coded signal in said subset of the frequency range above the first crossover frequency corresponding to the spectral content of the second waveform-coded signal. This is a preferred option when the second waveform-coded signal represents a transient component, for example when said subset of the frequency range above the first crossover frequency may therefore include a frequency interval extending between said first crossover frequency and a certain second crossover frequency. The replacement is typically performed only for the time range covered by the second waveform-coded signal. In this way, as little as possible can be replaced while still being sufficient to replace the transient components and potential time blurring present in the frequency-extended signal. Thus, the interleaving is not limited to the time segments specified by the SBR envelope time grid.

[0024] According to an exemplary embodiment, the first and second waveform-encoded signals may be separate signals, i.e. separately encoded, or alternatively, the first waveform-encoded signal and the second waveform-encoded signal form first and second signal portions of a common, jointly encoded signal, the latter option being more attractive from an implementation point of view.

[0025] According to an exemplary embodiment, the decoding method may include receiving a control signal including data relating to one or more time ranges and one or more frequency ranges above the first crossover frequency in which the second waveform-coded signal is available, where interleaving the frequency-extended signal with the second waveform-coded signal is based on the control signal. This is advantageous in that it provides an efficient way of controlling the interleaving.

[0026] According to an exemplary embodiment, the control signal includes at least one of a second vector indicating the one or more frequency ranges above the first crossover frequency over which the second waveform-encoded signal is available for interleaving with the frequency-extended signal and a third vector indicating the one or more time ranges over which the second waveform-encoded signal is available for interleaving with the frequency-extended signal, which is a convenient way of implementing the control signal.

[0027] According to an exemplary embodiment, the control signal includes a first vector indicating one or more frequency ranges above the first crossover frequency that are to be parametrically reconstructed based on the high-frequency reconstruction parameters. In this way, the frequency-extended signal may be prioritized over the second waveform-encoded signal for certain frequency bands.

[0028] According to an exemplary embodiment, there is also provided a computer program product having a computer readable medium having instructions for performing any of the decoding methods of the first aspect.

[0029] According to an exemplary embodiment, there is also provided a decoder for an audio processing system, the decoder comprising: a receiving stage configured to receive a first waveform-coded signal having a spectral content up to a first crossover frequency, a second waveform-coded signal having a spectral content corresponding to a subset of a frequency range above the first crossover frequency, and high-frequency reconstruction parameters; a high-frequency reconstruction stage receiving the first waveform-coded signal and the high-frequency reconstruction parameters from the receiving stage and performing high-frequency reconstruction using the first waveform-coded signal and the high-frequency reconstruction parameters to generate a frequency-extended signal having a spectral content above the first crossover frequency; and an interleaving stage receiving the frequency-extended signal from the high-frequency reconstruction stage and the second waveform-coded signal from the receiving stage, and interleaving the frequency-extended signal with the second waveform-coded signal.

[0030] According to an exemplary embodiment, the decoder may be configured to perform any of the decoding methods disclosed herein.

[0031] II. Overview - Encoders According to a second aspect, exemplary embodiments propose an encoding method, an encoding device and a computer program product for encoding. The proposed method, device and computer program product may generally have the same features and advantages.

[0032] The advantages of the features and setups presented in the decoder overview above may be generally valid for the corresponding features and setups for the encoder.

[0033] According to an exemplary embodiment, a method of encoding in an audio processing system is provided, the method including: receiving an audio signal to be encoded; calculating, based on the received audio signal, high-frequency reconstruction parameters enabling high-frequency reconstruction of the received audio signal above a first crossover frequency; identifying, based on the received audio signal, a subset of a frequency range above the first crossover frequency in which a spectral content of the received audio signal is to be waveform coded and then interleaved with the high-frequency reconstruction of the audio signal in a decoder; generating a first waveform-coded signal by waveform coding the received audio signal for a spectral band up to the first crossover frequency; and generating a second waveform-coded signal by waveform coding the received audio signal for a spectral band corresponding to the identified subset of the frequency range above the first crossover frequency.

[0034] According to an example embodiment, the subset of the frequency range above the first crossover frequency may include a number of isolated frequency intervals.

[0035] According to an example embodiment, the subset of the frequency range above a first crossover frequency may include a frequency interval extending between the first crossover frequency and a second crossover frequency.

[0036] According to an example embodiment, the second crossover frequency may vary as a function of time.

[0037] According to an exemplary embodiment, the high-frequency reconstruction parameters are calculated using Spectral Band Replication (SBR) encoding.

[0038] According to an exemplary embodiment, the encoding method may further comprise adjusting a spectral envelope level included in the high-frequency reconstruction parameters to compensate for the high-frequency reconstruction of the received audio signal being added with the second waveform-coded signal at the decoder. Since the second waveform-coded signal is added to the high-frequency reconstructed signal at the decoder, the spectral envelope level of the combined signal is different from the spectral envelope level of the high-frequency reconstructed signal. This change in the spectral envelope level may be taken into account at the encoder so that the combined signal at the decoder obtains a target spectral envelope. By performing the above adjustment at the encoder side, the intelligence required at the decoder side may be reduced. Or, in other words, specific signaling from the encoder to the decoder does not require defining specific rules at the decoder on how to handle the situation. This allows future optimization of the system due to future optimization of the encoder without the need to update the decoder, which may be widely deployed.

[0039] According to an exemplary embodiment, the step of adjusting the high-frequency reconstruction parameters may include measuring an energy of the second waveform-coded signal; and adjusting a spectral envelope level intended to control the spectral envelope of the high-frequency reconstructed signal by subtracting the measured energy of the second waveform-coded signal from a spectral envelope level for a spectral band corresponding to the spectral content of the second waveform-coded signal.

[0040] According to an exemplary embodiment, there is also provided a computer program product having a computer readable medium having instructions for performing any of the encoding methods of the second aspect.

[0041] According to an exemplary embodiment, an encoder for an audio processing system is provided, comprising: a receiving stage configured to receive an audio signal to be encoded; a high-frequency encoding stage configured to receive the audio signal from the receiving stage and to calculate, based on the received audio signal, high-frequency reconstruction parameters enabling high-frequency reconstruction of the received audio signal above a first crossover frequency; an interleave coding detection stage configured to identify, based on the received audio signal, a subset of a frequency range above the first crossover frequency in which a spectral content of the received audio signal is to be waveform coded and thereafter interleaved with the high-frequency reconstruction of the audio signal in a decoder; and a waveform coding stage configured to receive the audio signal from the receiving stage and generate a first waveform coded signal by waveform coding the received audio signal for a spectral band up to the first crossover frequency, receive the identified subset of frequency ranges above the first crossover frequency from the interleave coding detection stage, and generate a second waveform coded signal by waveform coding the received audio signal for a spectral band corresponding to the received identified subset of frequency ranges.

[0042] According to an exemplary embodiment, the encoder may further comprise an envelope adjustment stage configured to receive the high-frequency reconstruction parameters from the high-frequency encoding stage and the identified subset of the frequency range above the first crossover frequency from the interleaved coding detection stage, and to adjust, based on the received data, high-frequency reconstruction parameters to compensate for subsequent interleaving of the high-frequency reconstruction of the received audio signal with the second waveform-coded signal at a decoder.

[0043] According to an exemplary embodiment, the decoder may be configured to perform any of the decoding methods disclosed herein.

[0044] III. EXEMPLARY EMBODIMENTS - DECODERS 1 shows an exemplary embodiment of a decoder 100. The decoder comprises a receiving stage 110, a high-frequency reconstruction stage 120 and an interleaving stage .

[0045] The operation of the decoder 100 will now be described in more detail with reference to the exemplary embodiment of Fig. 2 showing a decoder 200 and the flow chart of Fig. 3. The objective of the decoder 200 is to provide an improved signal reconstruction for high frequencies when there are strong tonal components in the high frequency band of the audio signal to be reconstructed. The receiving stage 110 receives a first waveform-coded signal 201 in step D02. The first waveform-coded signal 201 has a spectral content up to a first crossover frequency fc. That is to say, the first waveform-coded signal 201 is a low-band signal that is limited to a frequency range below the first crossover frequency fc.

[0046] The receiving stage 110 receives the second waveform-encoded signal 202 in step D04. The second waveform-encoded signal 202 has a spectral content corresponding to a subset of the frequency range above the first crossover frequency fc. In the illustrated example of Fig. 2, the second waveform-encoded signal 202 has a spectral content corresponding to a number of isolated frequency intervals 202a and 202b. Thus, the second waveform-encoded signal 202 may be seen as being composed of a number of band-limited signals, each band-limited signal corresponding to one of the isolated frequency intervals 202a and 202b. In Fig. 2, only two frequency intervals 202a and 202b are shown. In general, the spectral content of the second waveform-encoded signal may correspond to any number of frequency intervals of various widths.

[0047] The receiving stage 110 may receive the first and second waveform-coded signals 201 and 202 as two separate signals. Alternatively, the first and second waveform-coded signals 201 and 202 may form first and second signal parts of a common signal received by the receiving stage 110. In other words, the first and second waveform-coded signals may be jointly coded, for example using the same MDCT transform.

[0048] Typically, the first waveform-coded signal 201 and the second waveform-coded signal 202 received by the receiving stage 110 are coded using an overlapping windowed transform, such as an MDCT transform. The receiving stage may comprise a waveform decoding stage 240 configured to transform the first and second waveform-coded signals 201 and 202 into the time domain. The waveform decoding stage 240 typically comprises an MDCT filter bank configured to perform an inverse MDCT transform of the first and second waveform-coded signals 201 and 202.

[0049] The receiving stage 110 further receives, in step D06, high-frequency reconstruction parameters to be used by the high-frequency reconstruction stage 120 disclosed below.

[0050] The first waveform-encoded signal 201 and the high-frequency parameters received by the receiving stage 110 are then input to the high-frequency reconstruction stage 120. The high-frequency reconstruction stage 120 typically operates in the frequency domain, preferably in the QMF domain. Therefore, before being input to the high-frequency reconstruction stage 120, the first waveform-encoded signal 201 is preferably transformed into the frequency domain, preferably into the QMF domain, by a QMF decomposition stage 250. The QMF decomposition stage 250 typically comprises a QMF filter bank configured to perform a QMF transformation of the first waveform-encoded signal 201.

[0051] Based on the first waveform-encoded signal 201 and the high-frequency reconstruction parameters, the high-frequency reconstruction stage 120 extends the first waveform-encoded signal 201 to frequencies above the first crossover frequency fc in step D08. More specifically, the high-frequency reconstruction stage 120 generates a frequency-extended signal 203 having a spectral content above the first crossover frequency fc. Thus, the frequency-extended signal 203 is a wideband signal.

[0052] The high-frequency reconstruction stage 120 may operate according to any known algorithm for performing high-frequency reconstruction. In particular, the high-frequency reconstruction stage 120 may be configured to perform SBR as disclosed in the review article by Friedrich Schmidt, "Sample-based Reconstruction of High-Frequency Signals," IEEE Transactions on Signal Processing, Vol. 13, No. 1, pp. 1171-1175, 2002. Thus, the high-frequency reconstruction stage may have several sub-stages configured to generate the frequency-extended signal 203 in several steps. For example, the high-frequency reconstruction stage 120 may have a high-frequency generation stage 221, a parametric high-frequency component addition stage 222 and an envelope adjustment stage 223.

[0053] Briefly, the high frequency generation stage 221 extends the first waveform-coded signal 201 to a frequency range above the crossover frequency fc in a first sub-step D08a in order to generate a frequency extended signal 203. This generation is performed by selecting subband parts of the first waveform-coded signal 201 and mirroring or copying the selected subband parts of the first waveform-coded signal 201 to selected subband parts of the frequency range above the first crossover frequency fc according to certain rules guided by high frequency reconstruction parameters.

[0054] The high frequency reconstruction parameters may further include missing harmonics parameters for adding missing harmonics to the frequency extended signal 203. As discussed above, missing harmonics are interpreted as any strong tonal part of the spectrum. For example, the missing harmonics parameters may include parameters related to the frequency and amplitude of the missing harmonics. Based on the missing harmonics parameters, the parametric high frequency component addition stage 222 generates sinusoidal components and adds the sinusoidal components to the frequency extended signal 203 in sub-step D08b.

[0055] The high-frequency reconstruction parameters may further comprise spectral envelope parameters describing a target energy level of the frequency extended signal 203. Based on the spectral envelope parameters, the envelope adjustment stage 223 adjusts in sub-step D08c the spectral content of the frequency extended signal 203, i.e. the spectral coefficients of the frequency extended signal 203, so that the energy level of the frequency extended signal 203 corresponds to the target energy level described by the spectral envelope parameters.

[0056] The frequency-expanded signal 203 from the high-frequency reconstruction stage 120 and the second waveform-coded signal from the receiving stage 110 are then input to the interleaving stage 130. The interleaving stage 130 typically operates in the same frequency domain as the high-frequency reconstruction stage 120, preferably in the QMF domain. Thus, the second waveform-coded signal 202 is typically input to the interleaving stage via a QMF decomposition stage 250. Furthermore, the second waveform-coded signal 202 is typically delayed by a delay stage 260 to compensate for the time it takes the high-frequency reconstruction stage 120 to perform the high-frequency reconstruction. In this way, the second waveform-coded signal 202 and the frequency-expanded signal 203 are aligned so that the interleaving stage 130 operates on signals corresponding to the same time frame.

[0057] The interleaving stage 130 then interleaves, i.e. combines, in step D10, the second waveform-coded signal 202 with the frequency-extended signal 203 to generate an interleaved signal 204. Various approaches can be used to interleave the second waveform-coded signal 202 with the frequency-extended signal 203.

[0058] According to an exemplary embodiment, the interleaving stage 130 interleaves the frequency-extended signal 203 with the second waveform-coded signal 202 by adding the frequency-extended signal 203 and the second waveform-coded signal 202. The spectral content of the second waveform-coded signal 202 overlaps the spectral content of the frequency-extended signal 203 in said subset of the frequency range corresponding to the spectral content of the second waveform-coded signal 202. By adding the frequency-extended signal 203 and the second waveform-coded signal 202, the interleaved signal 204 contains the spectral content of the frequency-extended signal 203 and the frequency content of the second waveform-coded signal 202 for the overlapping frequencies. As a result of the addition, the spectral envelope level of the interleaved signal 204 increases for the overlapping frequencies. Preferably, as disclosed below, the increase in the spectral envelope level due to the addition is taken into account at the encoder side when determining the energy envelope level to be included in the high-frequency reconstruction parameters. For example, the spectral envelope levels for the overlapping frequencies may be reduced at the encoder side by an amount that corresponds to the increase in the spectral envelope levels due to interleaving at the decoder side.

[0059] Alternatively, the increase in the spectral envelope level due to the addition may be taken into account on the decoder side, for example there may be an energy measurement stage which measures the energy of the second waveform-coded signal 202, compares the measured energy with a target energy level described by a spectral envelope parameter and adjusts the frequency extended signal 203 such that the spectral envelope level of the interleaved signal 204 is equal to the target energy level.

[0060] According to another exemplary embodiment, the interleaving stage 130 interleaves the frequency extended signal 203 with the second waveform encoded signal 202 by replacing the spectral content of the frequency extended signal 203 with the spectral content of the second waveform encoded signal 202 for frequencies where the frequency extended signal 203 and the second waveform encoded signal 202 overlap. In the exemplary embodiment where the frequency extended signal 203 is replaced by the second waveform encoded signal 202, it is not necessary to adjust the spectral envelope level to compensate for the interleaving of the frequency extended signal 203 and the second waveform encoded signal 202.

[0061] The high frequency reconstruction stage 120 preferably operates with a sampling rate equal to the sampling rate of the underlying core encoder used to encode the first waveform coded signal 201. In this way, the same overlapping windowed transform, such as the same MDCT, used to encode the first waveform coded signal 202 can be used to encode the second waveform coded signal 202.

[0062] The interleaving stage 130 may further be configured to receive a first waveform-encoded signal 201 from the receiving stage, preferably via a waveform decoding stage 240, a QMF decomposition stage 250 and a delay stage 260, and to combine the interleaved signal 204 with the first waveform-encoded signal 201 to generate a combined signal 205 having spectral content for frequencies below and above the first crossover frequency.

[0063] The output signal from interleaving stage 130 , ie, interleaved signal 204 or combined signal 205 , may then be transformed back to the time domain by QMF synthesis stage 270 .

[0064] Preferably, the QMF decomposition stage 250 and the QMF synthesis stage 270 have the same number of subbands. That is, the sampling rate of the signal input to the QMF decomposition stage 250 is equal to the sampling rate of the signal output from the QMF synthesis stage 270. As a result, the waveform coder (using MDCT) used to waveform code the first and second waveform-coded signals operates at the same sampling rate as the output signal. Thus, the first and second waveform-coded signals can be efficiently and structurally simply coded using the same MDCT transform. This is in contrast to the prior art, where the sampling rate of the waveform coder was typically limited to half the sampling rate of the output signal, and the subsequent high-frequency reconstruction module performed upsampling in addition to the high-frequency reconstruction. This limits the ability to waveform code frequencies covering the entire output frequency range.

[0065] Fig. 4 shows an exemplary embodiment of a decoder 400. The decoder 400 is intended to provide an improved signal reconstruction for high frequencies in the presence of transient components in the input audio signal to be reconstructed. The main difference between the example of Fig. 4 and the example of Fig. 2 is the shape of the spectral content and the duration of the second waveform-encoded signal.

[0066] 4 illustrates the operation of the decoder 400 during a number of subsequent time portions of a time frame. Here, three subsequent time portions are shown. A time frame may correspond, for example, to 2048 time samples. In particular, during a first time portion, the receiving stage 110 receives a first waveform-encoded signal 401a having a spectral content up to a first crossover frequency fc1. During the first time portion, a second waveform-encoded signal is not received.

[0067] During the second time portion, the receiving stage 110 receives a first waveform-encoded signal 401b having a spectral content up to a first crossover frequency fc1 and a second waveform-encoded signal 402b having a spectral content corresponding to a subset of the frequency range above the first crossover frequency fc1. In the illustrated example of Fig. 4, the second waveform-encoded signal 402b has a spectral content corresponding to a frequency interval extending between the first crossover frequency fc1 and a second crossover frequency fc2. Thus, the second waveform-encoded signal 402b is a band-limited signal that is limited to a frequency band between the first crossover frequency fc1 and the second crossover frequency fc2.

[0068] During the third time portion, the receiving stage 110 receives the first waveform-encoded signal 401c having a spectral content up to the first crossover frequency fc1. For the third time portion, the second waveform-encoded signal is not received.

[0069] For the first and third illustrated time portions, there is no second waveform-coded signal. For these time portions, the decoder operates like a normal decoder configured to perform high-frequency reconstruction, such as a conventional SBR decoder. The high-frequency reconstruction stage 120 generates frequency-extended signals 403a and 403c based on the first waveform-coded signals 401a and 401c, respectively. However, since there is no second waveform-coded signal, no interleaving is performed by the interleaving stage.

[0070] For the second illustrated time portion, there is a second waveform-coded signal 402b. For the second time portion, the decoder 400 operates in the same manner as described with respect to Fig. 2. In particular, the high-frequency reconstruction stage 120 performs high-frequency reconstruction based on the first waveform-coded signal and the high-frequency reconstruction parameters to generate a frequency-extended signal 403b. The frequency-extended signal 403b is then input to the interleaving stage 130, where it is interleaved with the second waveform-coded signal 402b into an interleaved signal 404b. As discussed in connection with the exemplary embodiment of Fig. 2, the interleaving may be performed using an additive or permutation approach.

[0071] In the above example, there is no second waveform-coded signal for the first and third time portions. For these time portions, the second crossover frequency is equal to the first crossover frequency and no interleaving is performed. For the second time frame, the second crossover frequency is greater than the first crossover frequency and interleaving is performed. In general, the second crossover frequency can thus vary as a function of time. In particular, the second crossover frequency can vary within a time frame. Interleaving is performed when the second crossover frequency is greater than the first crossover frequency and less than the maximum frequency represented by the decoder. If the second crossover frequency is equal to the maximum frequency, this corresponds to pure waveform coding and no high-frequency reconstruction is required.

[0072] It is noted that the embodiments described with respect to figures 2 and 4 may be combined. Figure 7 shows a time-frequency matrix 700 defined in the frequency domain, preferably in the QMF domain, where interleaving is performed by the interleaving stage 130. The illustrated time-frequency matrix 700 corresponds to one frame of the audio signal to be decoded. The illustrated matrix is ​​divided into 16 time slots and a number of frequency subbands starting from a first crossover frequency fc1. Furthermore, a first time range T1 covering the time range below the eighth time slot, a second time range T2 covering the eighth time slot and a third time range T3 covering the time slots above the eighth time slot are shown. As part of the SBR data, different spectral envelopes may be associated to the different time ranges T1 to T3.

[0073] In the present example, at the encoder side, two strong tonal components in frequency bands 710 and 720 have been identified in the audio signal. The frequency bands 710 and 720 may be of the same bandwidth as the SBR envelope band, i.e., the same frequency resolution used to represent the spectral envelope. These tonal components in bands 710 and 720 have a time range corresponding to a complete time frame, i.e., the time range of the tonal components includes the time ranges T1 to T3. At the encoder side, it has been decided to waveform-code the tonal components 710 and 720 during the first time range T1. This is indicated by the tonal components 710a and 720 being shaded during the first time range T1. Furthermore, at the encoder side, it has been decided that during the second and third time ranges T2 and T3 the first tonal component 710 should be parametrically reconstructed by the decoder by including a sinusoid as described in connection with the parametric high frequency component stage 222 of FIG. 2. This is illustrated by the orthogonal diagonal line pattern of the first tonal component 710b during the (second time range T2) and third time range T3. During the second and third time ranges T2 and T3, the second tonal component 720 is still waveform encoded. Furthermore, in this embodiment, the first and second tonal components are interleaved with the high frequency reconstructed audio signal by summation, so that the encoder adjusts the transmitted spectral envelope, the SBR envelope, accordingly.

[0074] Furthermore, at the encoder side, a transient component 730 has been identified in the audio signal. The transient component 730 has a duration corresponding to a second time range T2 and corresponds to a frequency interval between the first crossover frequency fc1 and the second crossover frequency fc2. At the encoder side, it has been decided to waveform-code the time-frequency portion of the audio signal corresponding to the location of the transient component. In this embodiment, the interleaving of the waveform-coded transient components is performed by substitution. A signaling scheme is set up to communicate this information to the decoder. The signaling scheme includes information related to in which time range and / or in which frequency range above the first crossover frequency fc1 the second waveform-coded signal is available. The signaling scheme may be associated with rules related to how the interleaving should be performed, i.e. whether the interleaving is by addition or by substitution. The signaling scheme may be associated with rules defining the priority of adding or substituting the various signals as explained below.

[0075] The signaling scheme includes a first vector 740, labeled "add sinusoid", which indicates whether a sinusoid should be parametrically added for each frequency subband. In FIG. 7, the addition of the first tonal component 710b in the second and third time ranges T2 and T3 is indicated by a "1" for the corresponding subband in the first vector 740. The signaling including the first vector 740 is known from the prior art. These are rules defined in prior art decoders for when a sinusoid is allowed to start. The rule is that for a particular subband, if a new sinusoid is detected, i.e., if the "add sinusoid" signaling of the first vector 740 goes from 0 in one frame to 1 in the next frame, then the sinusoid will start at the beginning of the frame, unless there is a transient event in that frame. In that case, the sinusoid will start at the transient component. In the illustrated example, there is a transient event 730 in the frame, which explains why the parametric reconstruction with a sinusoid for the frequency band 710 starts only after the transient event 730 .

[0076] The signaling scheme further includes a second vector 750 labeled "waveform-encoded". The second vector 750 indicates, for each frequency subband, whether a waveform-encoded signal is available for interleaving with the high-frequency reconstruction of the audio signal. In FIG. 7, the availability of a waveform-encoded signal for the first and second tonal components 710 and 720 is indicated by a "1" for the corresponding subband in the second vector 750. In the present example, the indication of the availability of waveform-encoded data in the second vector 750 is also an indication that the interleaving is performed by addition. However, in other embodiments, the indication of the availability of waveform-encoded data in the second vector 750 may be an indication that the interleaving is performed by substitution.

[0077] The signaling scheme further includes a third vector 760 labeled "waveform-encoded". The third vector 760 indicates, for each time slot, whether a waveform-encoded signal is available for interleaving with the high-frequency reconstruction of the audio signal. In FIG. 7, the availability of a waveform-encoded signal for the transient component 730 is indicated by a "1" for the corresponding time slot in the third vector 760. In the present example, the indication of the availability of waveform-encoded data in the third vector 760 is also an indication that interleaving is performed by substitution. However, in other embodiments, the indication of the availability of waveform-encoded data in the third vector 760 may be an indication that interleaving is performed by addition.

[0078] There are many alternative options for how to implement the first, second and third vectors 740, 750, 760. In some embodiments, the vectors 740, 750, 760 are binary vectors that use a logical 0 or a logical 1 to provide that indication. In other embodiments, the vectors 740, 750, 760 may take different forms. For example, a first value such as a "0" in the vector may indicate that no waveform encoded data is available for that particular frequency band or time slot. A second value such as a "1" in the vector may indicate that interleaving is performed by addition for that particular frequency band or time slot. A third value such as a "2" in the vector may indicate that interleaving is performed by permutation for that particular frequency band or time slot.

[0079] The above exemplary signaling schemes may be associated with priorities that may be applied in case of a collision. By way of example, the third vector 760, representing an interleaving of transient components by permutation, may have priority over the first and second vectors 740 and 750. Furthermore, the first vector 740 may have priority over the second vector 750. It is understood that any priority between the vectors 740, 750, 760 may be defined.

[0080] FIG. 8a shows the interleaving stage 130 of FIG. 1 in more detail. The interleaving stage 130 may include a signaling decode component 1301, a decision logic component 1302, and an interleaving component 1303. As discussed above, the interleaving stage 130 receives the second waveform-encoded signal 802 and the frequency-extended signal 803. The interleaving stage 130 may also receive a control signal 805. The signaling decode component 1301 decodes the control signal 805 into three parts corresponding to the first vector 740, the second vector 750, and the third vector 760 of the signaling scheme described with respect to FIG. 7. These are sent to the decision logic component 1302 which generates a time / frequency matrix 870 for the QMF frame indicating for which time / frequency tiles to use either the second waveform-encoded signal 802 or the frequency-extended signal 803 based on logic. The time / frequency matrix 870 is passed to the interleaving component 1303 and is used in interleaving the second waveform-encoded signal 802 with the frequency-extended signal 803 .

[0081] The decision logic component 1302 is shown in more detail in FIG. 8b. The decision logic component 1302 may include a time / frequency matrix generation component 13201 and a prioritization component 13022. The time / frequency generation component 13021 generates a time / frequency matrix 870 with time / frequency tiles corresponding to the current QMF frame. The time / frequency generation component 13021 includes information from the first vector 740, the second vector 750, and the third vector 760 in the time / frequency matrix. For example, as shown in FIG. 7, if there is a "1" (or more generally any number different from 0) in the second vector 750 for a frequency, the time / frequency tiles corresponding to the frequency are set to "1" (or more generally to the number present in the vector 750) in the time / frequency matrix 870, indicating that interleaving with the second waveform-coded signal 802 should be performed for those time / frequency tiles. Similarly, a "1" (or more generally any number different from 0) in the third vector 760 for a time slot indicates that the time / frequency tiles corresponding to said time slot are set to "1" (or more generally any number different from 0) in the time / frequency matrix 870, indicating that interleaving with the second waveform-coded signal 802 should be performed for those time / frequency tiles. Similarly, a "1" in the first vector 740 for a frequency indicates that the time / frequency tiles corresponding to said frequency are set to "1" in the time / frequency matrix 870, indicating that the output signal 804 should be based on the frequency-extended signal 803 that has been parametrically reconstructed for said frequency, e.g. by including a sinusoidal signal.

[0082] For some time / frequency tiles, there will be a collision between information from the first vector 740, the second vector 750 and the third vector 760. That is, two or more of the vectors 740-760 indicate a number different from 0, such as "1", for the same time / frequency tile of the time / frequency matrix 870. In such a situation, the prioritization component 13022 needs to make a decision on how to prioritize information from those vectors to remove the collision in the time / frequency matrix 870. More precisely, the prioritization component 13022 decides whether the output signal 804 should be based on the frequency-extended signal 803 (i.e. giving priority to the first vector 740), by interleaving the second waveform-coded signal 802 in the frequency direction (i.e. giving priority to the second vector 750) or by interleaving the second waveform-coded signal 802 in the time direction (i.e. giving priority to the third vector 750).

[0083] To this end, the prioritization component 13022 has predefined rules relating to the priorities of the vectors 740-760. The prioritization component 13022 may also have predefined rules relating to how the interleaving should be performed, i.e., whether the interleaving should be performed by addition or by substitution.

[0084] Preferably, these rules are as follows:

[0085] Interleaving in the time direction, i.e. the interleaving defined by the third vector 760, is given the highest priority. Interleaving in the time direction is preferably performed by permuting the frequency extended signal 803 in time / frequency tiles defined by the third vector 760. The time resolution of the third vector 760 corresponds to the time slots of the QMF frame. If the QMF frame corresponds to 2048 time domain samples, then a time slot may typically correspond to 128 time domain samples.

[0086] A parametric reconstruction of the frequency, i.e. using the frequency extended signal 803 defined by the first vector 740, is given the second highest priority. The frequency resolution of the first vector 740 is the frequency resolution of the QMF frame, such as the SBR envelope band. The prior art rules relating to the signalling and interpretation of the first vector 740 remain valid.

[0087] Interleaving in frequency direction, i.e. the interleaving defined by the second vector 750, is given the lowest priority. Interleaving in the frequency domain is performed by adding the frequency extended signal 803 in time / frequency tiles defined by the second vector 750. The frequency resolution of the second vector 750 corresponds to the frequency resolution of the QMF frame, such as the SBR envelope band.

[0088] III. EXEMPLARY EMBODIMENTS - ENCODERS 5 shows an exemplary embodiment of an encoder 500 suitable for use in an audio processing system. The encoder 500 comprises a receiving stage 510, a waveform encoding stage 520, a high-frequency encoding stage 530, an interleaved coding detection stage 540 and a transmission stage 550. The high-frequency encoding stage 530 may comprise a high-frequency reconstruction parameter calculation stage 530a and a high-frequency reconstruction parameter adjustment stage 530b.

[0089] The operation of the encoder 500 is described below with reference to the flow charts of figures 5 and 6. In step E02, the receiving stage 510 receives the audio signal to be encoded.

[0090] The received audio signal is input to the high-frequency encoding stage 530. Based on the received audio signal, the high-frequency encoding stage 530, in particular the high-frequency reconstruction parameter calculation stage 530a, calculates, in E04, high-frequency reconstruction parameters that enable high-frequency reconstruction of the received audio signal above a first crossover frequency fc. The high-frequency reconstruction parameter calculation stage 530a may use any known technique for calculating high-frequency reconstruction parameters, such as SBR encoding. The high-frequency encoding stage 530 typically operates in the QMF domain. Thus, before calculating the high-frequency reconstruction parameters, the high-frequency encoding stage 530 may perform a QMF decomposition of the received audio signal. As a result, the high-frequency reconstruction parameters are defined with respect to the QMF domain.

[0091] The calculated high-frequency reconstruction parameters may include some parameters related to high-frequency reconstruction. For example, the high-frequency reconstruction parameters may include parameters related to how to mirror or copy an audio signal from a selected subband part in a frequency range below the first crossover frequency fc to a subband part in a frequency range above the first crossover frequency fc. Such parameters are sometimes referred to as parameters describing a patching structure.

[0092] The high frequency reconstruction parameters may further include a spectral envelope parameter describing a target energy level of a subband portion of a frequency range above the first crossover frequency.

[0093] The high frequency reconstruction parameters may further include missing harmonic parameters indicating harmonics or strong tonal components that would be missing if the audio signal were reconstructed in a frequency range above the first crossover frequency using parameters describing the patching structure.

[0094] The interleaved coding detection stage 540 then identifies in step E06 a certain subset of the frequency range above the first crossover frequency fc in which the spectral content of the received audio signal should be waveform coded. In other words, the role of the interleaved coding detection stage 540 is to identify frequencies above the first crossover frequency in which high frequency reconstruction does not give the desired results.

[0095] The interleaved coding detection stage 540 may take different approaches to identify the relevant subset of the frequency range above the first crossover frequency fc. For example, the interleaved coding detection stage 540 may identify strong tonal components that are not well reconstructed by the high frequency reconstruction. The identification of strong tonal components may be based on the received audio signal, for example by determining the energy of the audio signal as a function of frequency and identifying frequencies with high energy as containing strong tonal components. Furthermore, the identification may be based on knowledge of how the received audio signal is reconstructed in the decoder. In particular, such identification may be based on a tonal quota, which is the ratio between a tonality measure of the received audio signal for the frequency band above the first crossover frequency and a tonality measure of the reconstruction of the received audio signal. A high tonal quota indicates that the audio signal is not well reconstructed for the frequencies corresponding to the tonal quota.

[0096] The interleaved coding detection stage 540 may also detect transient components of the received audio signal that are not well reconstructed by the high-frequency reconstruction. Such identification may be the result of a time-frequency analysis of the received audio signal. For example, a time-frequency interval in which the transient components appear may be detected from a spectrogram of the received audio signal. Such a time-frequency interval typically has a time range shorter than the time frame of the received audio signal. The corresponding frequency range typically corresponds to a frequency interval extending up to the second crossover frequency. Thus, said subset of the frequency range above the first crossover frequency may be identified by the interleaved coding detection stage 540 as an interval extending from the first crossover frequency to the second crossover frequency.

[0097] The interleaved coding detection stage 540 may further receive high-frequency reconstruction parameters from the high-frequency reconstruction parameter calculation stage 530a. Based on the missing harmonic parameters from the high-frequency reconstruction parameters, the interleaved coding detection stage 540 may identify the frequencies of the missing harmonics and decide to include at least some of the frequencies of the missing harmonics in the identified subset of the frequency range above the first crossover frequency fc. Such an approach may be advantageous when there are strong tonal components in the audio signal that cannot be properly modeled within the limits of a parametric model.

[0098] The received audio signal is also input to a waveform encoding stage 520. The waveform encoding stage 520 performs waveform encoding of the received audio signal in step E08. In particular, the waveform encoding stage 520 generates a first waveform-encoded signal by waveform encoding the audio signal for a spectral band up to a first crossover frequency fc. Furthermore, the waveform encoding stage 520 receives the identified subset from the interleaved coding detection stage 540. The waveform encoding stage 520 then generates a second waveform-encoded signal by waveform encoding the received audio signal for a spectral band corresponding to the identified subset of the frequency range above the first crossover frequency. Thus, the second waveform-encoded signal has a spectral content corresponding to the identified subset of the frequency range above the first crossover frequency fc.

[0099] According to an exemplary embodiment, the waveform encoding stage 520 may generate the first and second waveform-encoded signals by first waveform-encoding the received audio signal for all spectral bands and then removing the spectral content of the thus waveform-encoded signal for frequencies corresponding to an identified subset of frequencies above the first crossover frequency fc.

[0100] The waveform encoding stage may perform waveform encoding using, for example, an overlapping windowed transform filter bank, such as an MDCT filter bank. Such overlapping windowed transform filter banks use windows with a certain temporal length, so that the values ​​of the transformed signal in a certain time frame are influenced by the values ​​of the signal in the previous and following time frames. To mitigate the effects of this fact, it may be advantageous to perform a certain amount of temporal over-encoding. That is, the waveform encoding stage 520 waveform encodes not only the current time frame of the received audio signal, but also the previous and following time frames of the received audio signal. Similarly, the high-frequency encoding stage 530 may encode not only the current time frame of the received audio signal, but also the previous and following time frames of the received audio signal. In this way, an improved cross-fade between the second waveform-encoded signal and the high-frequency reconstruction of the audio signal can be achieved in the QMF domain. Furthermore, this reduces the need for adjustment of the spectral envelope data boundaries.

[0101] It is noted that the first and second waveform-encoded signals may be separate signals, but preferably they form the first and second waveform-encoded signal parts of a common signal, and if so, they may be generated by performing a single waveform encoding process on the received audio signal, for example by applying a single MDCT transform to the received audio signal.

[0102] The high-frequency encoding stage 530, in particular the high-frequency reconstruction parameter adjustment stage 530b, may also receive the identified subset of the frequency range above the first crossover frequency fc. Based on the received data, the high-frequency reconstruction parameter adjustment stage 530b may adjust the high-frequency reconstruction parameters in step E10. In particular, the high-frequency reconstruction parameter adjustment stage 530b may adjust the high-frequency reconstruction parameters corresponding to the spectral bands comprised in the identified subset.

[0103] For example, the high-frequency reconstruction parameter adjustment stage 530b may adjust a spectral envelope parameter describing a target energy level of the subband portion of the frequency range above the first crossover frequency. This is particularly important when the second waveform-coded signal is summed with the high-frequency reconstruction of the audio signal in the decoder, since in that case the energy of the second waveform-coded signal is added to the energy of the high-frequency reconstruction. To compensate for such summation, the high-frequency reconstruction parameter adjustment stage 530b may adjust the energy envelope parameter by subtracting the measured energy of the second waveform-coded signal from the target energy level for the spectral band corresponding to the identified subset of the frequency range above the first crossover frequency fc. In this way, the total signal energy is preserved when the second waveform-coded signal and the high-frequency reconstruction are summed in the decoder. The energy of the second waveform-coded signal may be measured, for example, by the interleaved coding detection stage 540.

[0104] The high-frequency reconstruction parameter adjustment stage 530b may also adjust the missing harmonic parameters. More specifically, if a subband containing a missing harmonic indicated by the missing harmonic parameters is part of the identified subset of the frequency range above the first crossover frequency fc, that subband is waveform coded by the waveform encoding stage 520. Thus, the high-frequency reconstruction parameter adjustment stage 530b may remove such missing harmonics from the missing harmonic parameters, since such missing harmonics do not need to be parametrically reconstructed at the decoder side.

[0105] A transmission stage 550 then receives the first and second waveform encoded signals from the waveform encoding stage 520 and the high-frequency reconstruction parameters from the high-frequency encoding stage 530. The transmission stage 550 formats the received data into a bitstream for transmission to a decoder.

[0106] The interleave coding detection stage 540 may further signal information to the transmission stage 550 for inclusion in the bitstream. In particular, the interleave coding detection stage 540 may signal how the second waveform-coded signal should be interleaved with the high-frequency reconstruction of the audio signal, for example whether interleaving should be performed by adding the signals or by replacing one of the signals with the other, and for which frequency ranges and for which time intervals the waveform-coded signal should be interleaved. For example, the signaling may be performed using the signaling scheme discussed with reference to FIG. 7.

[0107] Equivalents, extensions, replacements, etc. Further embodiments of the present disclosure will be apparent to those skilled in the art upon reviewing the above description. Although the present text and drawings disclose embodiments and examples, the present disclosure is not limited to these specific examples. Numerous modifications and variations can be made without departing from the scope of the present disclosure defined by the appended claims. Any reference signs appearing in the claims shall not be construed as limiting the scope thereof.

[0108] Moreover, variations to the disclosed embodiments can be understood and implemented by those skilled in the art in practicing the present disclosure, from an examination of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the singular does not exclude a plurality. The mere fact that certain features are recited in mutually different dependent claims does not indicate that a combination of these features cannot be used to advantage.

[0109] The systems and methods disclosed above may be implemented as software, firmware, hardware or a combination thereof. In hardware implementations, the division of tasks among functional units mentioned in the above description does not necessarily correspond to a division into physical units. Rather, one physical component may have multiple functions and one task may be performed by several physical components in cooperation. Some or all of the components may be implemented as software executed by a digital signal processor or microprocessor, or may be implemented as hardware or as an application specific integrated circuit. Such software may be distributed on a computer readable medium, which may include computer storage media (or non-transitory media) and communication media (or transitory media). As is well known to those skilled in the art, the term computer storage media includes volatile and non-volatile, removable and non-removable media implemented in any method or technology for storage of information such as computer readable instructions, data structures, program modules or other data. Computer storage media includes, but is not limited to, RAM, ROM, EEPROM, flash memory or other memory technology, CD-ROM, digital versatile disks (DVD) or other optical disk storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to store desired information and that can be accessed by a computer. Additionally, those skilled in the art will recognize that communication media typically embodies computer-readable instructions, data structures, program modules or other data in a modulated data signal, such as a carrier wave or other transport mechanism, and includes any information delivery media.

[0110] Several aspects will be described. [Aspect 1] 1. A method of decoding in an audio processing system, comprising: receiving a first waveform-encoded signal having a spectral content up to a first crossover frequency; receiving a second waveform-encoded signal having a spectral content corresponding to a subset of a frequency range above the first crossover frequency; receiving high frequency reconstruction parameters; performing high-frequency reconstruction using the first waveform-encoded signal and the high-frequency reconstruction parameters to generate a frequency extended signal having spectral content above the first crossover frequency; interleaving the frequency extended signal with the second waveform encoded signal; How to decode. [Aspect 2] 2. The decoding method of claim 1, wherein the subset of the frequency range above the first crossover frequency includes a plurality of isolated frequency intervals. [Aspect 3] 2. The decoding method of claim 1, wherein the subset of the frequency band above the first crossover frequency includes a frequency interval extending between the first crossover frequency and a second crossover frequency. Aspect 4 4. The decoding method of claim 3, wherein the second crossover frequency varies as a function of time. Aspect 5 5. The decoding method of claim 3 or 4, wherein the second crossover frequency varies within a time frame set by the audio processing system. Aspect 6 6. The decoding method of any one of aspects 1 to 5, wherein the step of performing high-frequency reconstruction comprises performing Spectral Band Replication (SBR). Aspect 7 7. The decoding method according to any one of aspects 1 to 6, wherein the step of performing high frequency reconstruction is performed in the frequency domain. Aspect 8 8. The decoding method of any one of aspects 1 to 7, wherein interleaving the frequency extended signal with the second waveform encoded signal is performed in the frequency domain. Aspect 9 8. The decoding method of claim 6 or 7, wherein the frequency domain is a quadrature mirror filter (QMF) domain. Aspect 10 10. The decoding method of any one of aspects 1 to 9, wherein the received first and second waveform-coded signals are coded using the same MDCT transform. Aspect 11 11. The decoding method of any one of aspects 1 to 10, further comprising adjusting a spectral content of the frequency extended signal according to the high-frequency reconstruction parameter, thereby adjusting a spectral envelope of the frequency extended signal. Aspect 12 12. The method of decoding of any one of aspects 1-11, wherein the interleaving step comprises adding the second waveform-encoded signal to the frequency-extended signal. Aspect 13 12. The decoding method of any one of aspects 1 to 11, wherein the interleaving step includes replacing the spectral content of the frequency extended signal with the spectral content of the second waveform coded signal in the subset of frequency ranges above the first crossover frequency corresponding to the spectral content of the second waveform coded signal. Aspect 14 14. The decoding method of any one of aspects 1 to 13, wherein the first waveform-encoded signal and the second waveform-encoded signal form first and second signal parts of a common signal. Aspect 15 15. The decoding method of any one of aspects 1 to 14, further comprising receiving a control signal including data relating to one or more time ranges and one or more frequency ranges above the first crossover frequency in which the second waveform-coded signal is available, and wherein the step of interleaving the frequency-extended signal with the second waveform-coded signal is based on the control signal. Aspect 16 16. The decoding method of claim 15, wherein the control signal includes at least one of a second vector indicating the one or more frequency ranges above the first crossover frequency in which the second waveform-coded signal is available for interleaving with the frequency-extended signal, and a third vector indicating the one or more time ranges in which the second waveform-coded signal is available for interleaving with the frequency-extended signal. Aspect 17 A decoding method according to aspect 15 or 16, wherein the control signal includes a first vector indicating one or more frequency ranges above the first crossover frequency that are to be parametrically reconstructed based on the high-frequency reconstruction parameters. Aspect 18 18. A computer program product having a computer readable medium having instructions for performing the decoding method according to any one of embodiments 1 to 17. Aspect 19 1. A decoder for an audio processing system comprising: a receiving stage configured to receive a first waveform-encoded signal having a spectral content up to a first crossover frequency, a second waveform-encoded signal having a spectral content corresponding to a subset of a frequency range above the first crossover frequency, and high-frequency reconstruction parameters; a high frequency reconstruction stage that receives the first waveform-encoded signal and the high frequency reconstruction parameters from the receiving stage and performs high frequency reconstruction using the first waveform-encoded signal and the high frequency reconstruction parameters to generate a frequency extended signal having spectral content above the first crossover frequency; an interleaving stage for receiving the frequency extended signal from the high frequency reconstruction stage and the second waveform encoded signal from the receiving stage and for interleaving the frequency extended signal with the second waveform encoded signal. decoder. Aspect 20 1. A method of encoding in an audio processing system, comprising: receiving an audio signal to be encoded; calculating, based on the received audio signal, high-frequency reconstruction parameters enabling high-frequency reconstruction of the received audio signal above a first crossover frequency; identifying, based on the received audio signal, a subset of a frequency range above the first crossover frequency within which the spectral content of the received audio signal is to be waveform coded and then interleaved with a high frequency reconstruction of the audio signal at a decoder; generating a first waveform-coded signal by waveform coding the received audio signal for a spectral band up to a first crossover frequency, and generating a second waveform-coded signal by waveform coding the received audio signal for a spectral band corresponding to the identified subset of a frequency range above the first crossover frequency. The encoding method. Aspect 21 21. The encoding method of claim 20, wherein the subset of the frequency range above the first crossover frequency includes a plurality of isolated frequency intervals. Aspect 22 22. The encoding method of claim 20 or 21, wherein the subset of the frequency range above the first crossover frequency includes a frequency interval extending between the first crossover frequency and a second crossover frequency. Aspect 23 23. The encoding method of embodiment 22, wherein the second crossover frequency varies as a function of time. Aspect 24 22. The encoding method of embodiment 20 or 21, wherein the high-frequency reconstruction parameters are calculated using Spectral Band Replication (SBR) encoding. Aspect 25 25. The encoding method of any one of aspects 20 to 24, further comprising a step of adjusting a spectral envelope level included in the high-frequency reconstruction parameters to ensure that high-frequency reconstruction of the received audio signal is added to the second waveform-coded signal at a decoder. Aspect 26 The step of adjusting the high frequency reconstruction parameters comprises: measuring an energy of the second waveform-encoded signal; adjusting the spectral envelope level by subtracting the measured energy of the second waveform encoded signal from the spectral envelope level for a spectral band corresponding to the spectral content of the second waveform encoded signal. The encoding method according to embodiment 25. Aspect 27 A computer program product having a computer-readable medium having instructions for performing the encoding method described in any one of aspects 20 to 26. Aspect 28 13. An encoder for an audio processing system comprising: a receiving stage configured to receive an audio signal to be encoded; a high frequency encoding stage configured to receive the audio signal from the receiving stage and to calculate, based on the received audio signal, high frequency reconstruction parameters enabling high frequency reconstruction of the received audio signal above a first crossover frequency; an interleave coding detection stage configured to identify, based on the received audio signal, a subset of a frequency range above the first crossover frequency in which the spectral content of the received audio signal should be waveform coded and then interleaved with a high frequency reconstruction of the audio signal in a decoder; a waveform encoding stage configured to receive the audio signal from the receiving stage and generate a first waveform-coded signal by waveform coding the received audio signal for a spectral band up to a first crossover frequency, and to receive the identified subset of frequency ranges above the first crossover frequency from the interleaved coding detection stage and generate a second waveform-coded signal by waveform coding the received audio signal for a spectral band corresponding to the received identified subset of frequency ranges. Encoder. Aspect 29 29. The encoder of claim 28, further comprising an envelope adjustment stage configured to receive the high-frequency reconstruction parameters from the high-frequency encoding stage and the identified subset of the frequency range above the first crossover frequency from the interleave encoding detection stage, and to adjust the high-frequency reconstruction parameters based on the received data to compensate for subsequent interleaving of the high-frequency reconstruction of the received audio signal with the second waveform-coded signal at a decoder.

Claims

1. 1. A method of decoding an audio signal in an audio processing system, comprising: receiving a first waveform-encoded signal having a spectral content up to a first crossover frequency; receiving a second waveform-encoded signal having spectral content corresponding to a subset of a frequency range above the first crossover frequency; performing high-frequency reconstruction using at least a portion of the first waveform-coded signal and high-frequency reconstruction parameters to generate a frequency extended signal having spectral content above the first crossover frequency, the high-frequency reconstruction adjusting energy levels of subbands of the frequency extended signal based on target energy levels for those subbands, the high-frequency reconstruction being performed in the frequency domain; and interleaving the frequency extended signal with the second waveform coded signal to generate an interleaved signal, such that energy levels for subbands of the interleaved signal are based on the target energy levels for those subbands. method.

2. The method of claim 1 , wherein the spectral content of the second waveform-encoded signal overlaps the spectral content of the frequency-extended signal in the subset of the frequency range above the first crossover frequency.

3. 2. The method of claim 1, wherein adjusting the energy levels of subbands of the frequency extension signal comprises subtracting the energy levels of subbands of the frequency extension signal from the target energy levels for those subbands.

4. The method of claim 1 , further comprising the step of combining the frequency extended signal, the second waveform encoded signal and the first waveform encoded signal.

5. The method of claim 1 , wherein the step of performing high frequency reconstruction comprises copying lower frequency bands into higher frequency bands.

6. The method of claim 1 , further comprising adjusting a spectral content of the frequency-extended signal according to the high-frequency reconstruction parameters to adjust a spectral envelope of the frequency-extended signal.

7. The method of claim 1 , wherein said interleaving comprises adding said second waveform-encoded signal to said frequency-extended signal.

8. 2. The method of claim 1, wherein the interleaving replaces the spectral content of the frequency-extended signal by the spectral content of the second waveform-encoded signal in the subset of the frequency range above the first crossover frequency that corresponds to the spectral content of the second waveform-encoded signal.

9. A non-transitory computer readable medium storing instructions that, when executed by a processor, cause the processor to perform the method of claim 1.

10. 1. An apparatus for decoding an encoded audio signal, comprising: an input interface configured to receive a first waveform-encoded signal having spectral content up to a first crossover frequency and a second waveform-encoded signal including spectral content corresponding to a subset of a frequency range above the first crossover frequency; a high-frequency reconstructor configured to receive the first waveform-encoded signal and high-frequency reconstruction parameters and to perform high-frequency reconstruction using the first waveform-encoded signal and the high-frequency reconstruction parameters to generate a frequency-extended signal having spectral content above the first crossover frequency, the high-frequency reconstruction adjusting energy levels of subbands of the frequency-extended signal based on target energy levels for those subbands, the high-frequency reconstruction being performed in the frequency domain; an interleaver configured to receive the frequency extended signal from the high frequency reconstructor and the second waveform coded signal from the input interface and to interleave the frequency extended signal with the second waveform coded signal to generate an interleaved signal, wherein an energy level for a subband of the interleaved signal is based on the target energy level. Device.

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