Decoding method and decoder for an audio signal, medium and encoding method

Abstract

The present disclosure relates to a decoding method and a decoder for audio signals, a medium and an encoding method. Methods and apparatuses for decoding and encoding of audio signals are provided. In particular, the method for decoding comprises receiving a waveform encoded signal having spectral content corresponding to a subset of a frequency range above a crossover frequency. The waveform encoded signal is interleaved with a parametric high frequency reconstruction of the audio signal above the crossover frequency. In this way, an improved reconstruction of the high frequency band of the audio signal is achieved.

Description

[0001] This application is a divisional application of patent application No. 201910557659.X, filed on April 4, 2014, entitled "A method and decoder for decoding audio signals, medium and encoding method". Patent application No. 201910557659.X is a divisional application of patent application No. 201480019104.5, filed on April 4, 2014, entitled "Audio encoder and decoder for interlaced waveform encoding". Technical Field

[0002] The invention disclosed herein generally relates to audio encoding and decoding. In particular, it relates to audio encoders and audio decoders suitable for performing high-frequency reconstruction of audio signals. Background Technology

[0003] Audio coding systems employ various methods for audio coding, such as pure waveform coding, parameter-space coding, and high-frequency reconstruction algorithms incorporating Spectral Band Replication (SBR). The MPEG-4 standard combines SBR and waveform coding of the audio signal. More precisely, the encoder waveform-codes the audio signal for the spectral bands up to the crossover frequency and encodes the spectral bands above the crossover frequency using SBR coding. The waveform-coded portion of the audio signal is then passed to the decoder along with the SBR parameters determined in the SBR coding. As discussed in the review paper 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, 2009, Article ID 468971, based on the waveform-coded portion of the audio signal and the SBR parameters, the decoder then reconstructs the audio signal in the spectral bands above the crossover frequency.

[0004] One problem with this method is that strong tonal components, i.e. strong harmonic components, or any components in the high-frequency band that are not properly reconstructed by the SBR algorithm, are missing in the output.

[0005] Therefore, the SBR algorithm implements the missing harmonic detection process. Tonal components that cannot be properly reconstructed by the high-frequency reconstruction of SBR are identified on the encoder side. The frequency location information of these strong tonal components is transmitted to the decoder, where the spectral content of the frequency band where the missing tonal component is located is replaced with a sine curve generated in the decoder.

[0006] The advantage of missing harmonic detection provided in the SBR algorithm is that it is a very low bit rate solution because, by some degree of simplification, only the frequency position of the tone component and its amplitude level need to be transmitted to the decoder.

[0007] The drawback of the SBR algorithm for missing harmonic detection is that it is a very coarse model. Another drawback is that when the transmission rate is low (i.e., when the number of bits that can be transmitted per second is low) and therefore the spectral bandwidth is wide, a sine curve will be used instead of a large frequency range.

[0008] Another drawback of the SBR algorithm is its tendency to erase transients present in the audio signal. Generally, transient pre-echo and post-echo will be present in the SBR-reconstructed audio signal. Therefore, further improvement is needed. Attached Figure Description

[0009] Hereinafter, exemplary embodiments will be described in more detail with reference to the accompanying drawings, wherein,

[0010] Figure 1 This is a schematic diagram of a decoder according to an exemplary embodiment;

[0011] Figure 2 This is a schematic diagram of a decoder according to an exemplary embodiment;

[0012] Figure 3 This is a flowchart of a decoding method according to an exemplary embodiment;

[0013] Figure 4 This is a schematic diagram of a decoder according to an exemplary embodiment;

[0014] Figure 5 This is a schematic diagram of an encoder according to an exemplary embodiment;

[0015] Figure 6 This is a flowchart of an encoding method according to an exemplary embodiment;

[0016] Figure 7 This is a schematic diagram of a signaling scheme according to an exemplary embodiment; and

[0017] Figure 8a ~b is a schematic diagram of an interleaving level according to an exemplary embodiment.

[0018] All accompanying drawings are schematic, and in order to clarify this disclosure, only the necessary parts are generally shown, while other parts may be omitted or merely suggested. Unless otherwise indicated, similar reference numerals refer to similar parts in different drawings. Detailed Implementation

[0019] In view of the above, one objective is to provide encoders and decoders, and related methods, that can improve the reconstruction of tonal components and transients in the high-frequency band.

[0020] I. Overview – Decoder

[0021] Here, the audio signal can be a pure audio signal, an audio-visual signal or the audio portion of a multimedia signal, or metadata combined with any of them.

[0022] According to the first aspect, exemplary embodiments provide a decoding method, decoding apparatus, and computer program product for decoding. The proposed method, apparatus, and computer program product generally have the same features and advantages.

[0023] According to an exemplary embodiment, a decoding method in an audio processing system is provided, the decoding method comprising: receiving a first waveform encoded signal having spectral content up to a first cross frequency; receiving a second waveform encoded signal having spectral content corresponding to a subset of frequency ranges above the first cross frequency; receiving high-frequency reconstruction parameters; performing high-frequency reconstruction by using the first waveform encoded signal and the high-frequency reconstruction parameters to generate a frequency spread signal having spectral content above the first cross frequency; and interleaving the frequency spread signal with the second waveform encoded signal.

[0024] Here, the waveform-encoded signal is to be interpreted as the signal encoded by direct quantization of the waveform representation; preferably, it is the linear quantization of the frequency transformation of the input waveform signal. This contrasts with parametric encoding, where the signal is represented by variations in a general model of signal properties.

[0025] The decoding method therefore suggests using waveform-encoded data from a subset of the frequency range above the first crossover frequency and interleaving it with the high-frequency reconstructed signal. In this way, important parts of the signal in the frequency band above the first crossover frequency, such as transient or tonal components that generally cannot be well reconstructed by parametric high-frequency reconstruction algorithms, can be waveform-encoded. As a result, the reconstruction of these important parts of the signal in the frequency band above the first crossover frequency is improved.

[0026] According to an exemplary embodiment, the subset of frequencies above the first crossover frequency is a sparse subset. For example, it may comprise multiple isolated frequency intervals. This is advantageous because the number of bits used to encode the second waveform coded signal is low. Furthermore, by having multiple isolated frequency intervals, the tonal components of the audio signal, such as single harmonics, can be well captured by the second waveform coded signal. As a result, improved reconstruction of the tonal components in the high-frequency band is achieved at a low bit cost.

[0027] Here, a missing harmonic or a single harmonic means any arbitrary strong tonal portion of the spectrum. In particular, it should be understood that a missing harmonic or a single harmonic is not limited to a single harmonic in a harmonic series.

[0028] According to an exemplary embodiment, the second waveform-encoded signal may represent a transient in the audio signal to be reconstructed. The transient is generally limited to a short time range, such as nearly a hundred time samples at a sampling rate of 48 kHz, for example, a time range on the order of 5 to 10 milliseconds, but may have a wide frequency range. To capture the transient, a subset of the frequency range above the first crossover frequency may therefore be included in the frequency interval extending between the first crossover frequency and the second crossover frequency. This is advantageous because improved reconstruction of the transient can be achieved.

[0029] According to an exemplary embodiment, the second cross frequency changes over time. For example, the second cross frequency can be changed within a time frame set by the audio processing system. In this way, transient short time ranges can be addressed.

[0030] According to an exemplary embodiment, the step of performing high-frequency reconstruction includes performing spectral band replication, i.e., SBR. High-frequency reconstruction is typically performed in the frequency domain, such as the domain of a pseudo-orthogonal mirror filter (QMF) with, for example, 64 sub-bands.

[0031] According to an exemplary embodiment, the step of interleaving the frequency spread signal and the second waveform encoded signal is performed in the frequency domain, such as the QMF domain. Generally, in order to facilitate implementation and better control of the time and frequency characteristics of these two signals, the interleaving is performed in the same frequency domain as the high-frequency reconstruction.

[0032] According to an exemplary embodiment, the received first and second waveform encoded signals are encoded using the same modified discrete cosine transform (MDCT).

[0033] According to an exemplary embodiment, the decoding method may include adjusting the spectral content of the frequency spread signal according to high-frequency reconstruction parameters to adjust the spectral envelope of the frequency spread signal.

[0034] According to an exemplary embodiment, interleaving may include adding a second waveform-encoded signal to a frequency-spread signal. This is a preferred option if the second waveform-encoded signal represents a tonal component, such as when a subset of the frequency range above the first crossover frequency contains multiple isolated frequency intervals. Adding the second waveform-encoded signal to the frequency-spread signal mimics the parameter addition of known harmonics in the SBR and allows the use of the SBR replica signal to avoid large frequency ranges being replaced by a single tonal component through an appropriate degree of blending.

[0035] According to an exemplary embodiment, interleaving includes replacing the spectral content of the frequency spread signal with the spectral content of the second waveform-coded signal in a 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, for example, when the subset of the frequency range above the first crossover frequency can therefore be included in the frequency interval extending between the first crossover frequency and the second crossover frequency. Generally, the replacement is performed only for the time range covered by the second waveform-coded signal. In this way, the replacement can be minimized while still being sufficient to replace transients and potential time erasures present in the frequency spread signal, and the interleaving is thus not limited to the time period defined by the SBR envelope time grid.

[0036] According to an exemplary embodiment, the first and second waveform encoded signals can be separate signals, meaning they are encoded separately. Alternatively, the first and second waveform encoded signals form the first and second signal portions of a common joint encoded signal. From an implementation perspective, this latter alternative is more attractive.

[0037] According to an exemplary embodiment, the decoding method may include receiving a control signal containing data relating to one or more time ranges available for a second waveform encoded signal and one or more frequency ranges above a first crossover frequency, wherein the step of interleaving the frequency spread signal with the second waveform encoded signal is based on the control signal. This is advantageous because it provides an efficient way to control the interleaving.

[0038] According to an exemplary embodiment, the control signal includes at least one of a second vector indicating that the second waveform encoded signal can be used to interleave with the frequency spread signal at one or more frequency ranges above the first crossover frequency, and a third vector indicating that the second waveform encoded signal can be used to interleave with the frequency spread signal at one or more time ranges. This is a convenient way to implement the control signal.

[0039] 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 reconstructed on the parameters based on high-frequency reconstruction parameters. In this way, for a certain frequency band, the frequency spread signal may take precedence over the second waveform-coded signal.

[0040] According to an exemplary embodiment, a computer program product is also provided, including a computer-readable medium having instructions for performing any decoding method of the first aspect.

[0041] According to an exemplary embodiment, a decoder for an audio processing system is also provided, the decoder comprising: a receiver stage configured to receive a first waveform-coded signal having spectral content up to a first cross frequency, a second waveform-coded signal having spectral content corresponding to a subset of frequency ranges above the first cross frequency, and high-frequency reconstruction parameters; a high-frequency reconstruction stage configured to receive the first waveform-coded signal and the high-frequency reconstruction parameters from the receiver stage and perform high-frequency reconstruction using the first waveform-coded signal and the high-frequency reconstruction parameters to generate a frequency-spread signal having spectral content above the first cross frequency; and an interleaving stage configured to receive the frequency-spread signal from the high-frequency reconstruction stage and receive the second waveform-coded signal from the receiver stage and interleave the frequency-spread signal with the second waveform-coded signal.

[0042] According to an exemplary embodiment, the decoder may be configured to perform any decoding method disclosed herein.

[0043] II. Overview – Encoder

[0044] According to the second aspect, exemplary embodiments provide encoding methods, encoding apparatus, and computer program products for encoding. The proposed methods, apparatus, and computer program products generally possess the same features and advantages.

[0045] For the corresponding features and settings used in the encoder, the advantages regarding features and settings given in the decoder overview above will generally be effective.

[0046] According to an exemplary embodiment, an encoding method in an audio processing system is provided, the encoding method comprising the steps of: receiving an audio signal to be encoded; calculating, based on the received audio signal, high-frequency reconstruction parameters that enable high-frequency reconstruction of the received audio signal above a first crossover frequency; identifying, based on the received audio signal, a subset of frequency ranges above the first crossover frequency, for which the spectral content of the received audio signal is waveform encoded and subsequently interleaved with high-frequency reconstruction of the audio signal in a decoder; generating a first waveform encoded signal by waveform encoding the received audio signal for a spectral band up to the first crossover frequency; and generating a second waveform encoded signal by waveform encoding the received audio signal for a spectral band corresponding to the identified subset of frequency ranges above the first crossover frequency.

[0047] According to an exemplary embodiment, a subset of the frequency range above the first cross frequency may include multiple isolated frequency intervals.

[0048] According to an exemplary embodiment, a subset of the frequency range above the first cross frequency may be included in the frequency interval extending between the first cross frequency and the second cross frequency.

[0049] According to an exemplary embodiment, the second cross frequency may change over time.

[0050] According to an exemplary embodiment, high-frequency reconstruction parameters are calculated by using spectral band replication (i.e., SBR) coding.

[0051] According to an exemplary embodiment, the encoding method may further include adjusting the spectral envelope level included in the high-frequency reconstruction parameters to compensate for the addition of the high-frequency reconstruction of the received audio signal and the second waveform encoded signal in the decoder. Since the second waveform encoded signal is added to the high-frequency reconstruction signal in the decoder, the spectral envelope level of the combined signal differs from that of the high-frequency reconstruction signal. This change in the spectral envelope level can be addressed in the encoder so that the combined signal in the decoder obtains the target spectral envelope. By performing this adjustment on the encoder side, the work required on the decoder side can be reduced, or in other words, by using specific signaling from the encoder to the decoder, it is not necessary to define specific rules in the decoder on how to handle this situation. This allows for future optimization of the system by optimizing the encoder in the future, without having to update the potentially widely deployed decoder.

[0052] According to an exemplary embodiment, the step of adjusting the high-frequency reconstruction parameters may include: measuring the energy of the second waveform coded signal; and adjusting the spectral envelope level by subtracting the measured energy of the second waveform coded signal from the spectral envelope level of the spectral band corresponding to the spectral content of the second waveform coded signal, in order to control the spectral envelope of the high-frequency reconstruction signal.

[0053] According to an exemplary embodiment, a computer program product is also provided, comprising a computer-readable medium having instructions for performing any coded method of the second aspect.

[0054] According to an exemplary embodiment, an encoder for an audio processing system is provided, the encoder comprising: a receiver stage configured to receive an audio signal to be encoded; a high-frequency encoding stage configured to receive the audio signal from the receiver stage and 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 interleaved coding detection stage configured to identify a subset of frequency ranges above the first crossover frequency based on the received audio signal, for which the spectral content of the received audio signal is waveform encoded and subsequently interleaved with high-frequency reconstruction of the audio signal in a decoder; and a waveform encoding stage configured to receive the audio signal from the receiver stage and generate a first waveform encoded signal by waveform encoding the received audio signal for a spectral band up to the 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 encoded signal by waveform encoding the received audio signal for a spectral band corresponding to the identified subset of the received frequency range.

[0055] According to an exemplary embodiment, the encoder may further include: an envelope adjustment stage configured to receive high-frequency reconstruction parameters from a high-frequency coding stage and an identified subset of a frequency range above a first cross frequency from an interleaved coding detection stage, and to adjust the high-frequency reconstruction parameters based on the received data to compensate for the interleaving of high-frequency reconstruction of the received audio signal with the second waveform coded signal in the decoder.

[0056] According to an exemplary embodiment, the encoder may be configured to perform any encoding method disclosed herein.

[0057] III. Exemplary Model – Decoder

[0058] Figure 1 An exemplary embodiment of decoder 100 is shown. The decoder includes a receiver stage 110, a high-frequency reconstruction stage 120, and an interleaving stage 130.

[0059] Now refer to the diagram showing decoder 200 Figure 2 Exemplary embodiments and Figure 3 The flowchart explains the operation of decoder 100 in more detail. The purpose of decoder 200 is to improve signal reconstruction at high frequencies when strong tonal components exist in the high-frequency band of the audio signal to be reconstructed. Receiver stage 110 receives the first waveform encoded signal 201 in step D02. The first waveform encoded signal 201 has frequencies up to the first crossover frequency f. c The spectral content, that is, the first waveform coded signal 201, is limited to a frequency below the first crossover frequency f. c Low-band signals in the frequency range.

[0060] In step D04, receiver 110 receives the second waveform encoded signal 202. The second waveform encoded signal 202 has a frequency higher than the first crossover frequency f. c The spectral content corresponding to a subset of the frequency range. Figure 2 In the illustrated example, the second waveform encoded signal 202 has spectral content corresponding to a plurality of isolated frequency intervals 202a and 202b. The second waveform encoded signal 202 can thus be considered as consisting of a plurality of band-limited signals, each band-limited signal corresponding to one of the isolated frequency intervals 202a and 202b. Figure 2 In the diagram, only two frequency intervals, 202a and 202b, are shown. Generally, the spectral content of the second waveform-coded signal can correspond to any number of frequency intervals with varying widths.

[0061] Receiver stage 110 can receive first and second waveform-encoded signals 201 and 202 as two separate signals. Alternatively, the first and second waveform-encoded signals 201 and 202 can form first and second signal portions of a common signal received by receiver stage 110. In other words, the first and second waveform-encoded signals can be jointly encoded, for example, by using the same MDCT transform.

[0062] Generally, the first waveform encoded signal 201 and the second waveform encoded signal 202 received by the receiver stage 110 are encoded using an overlapping window transform, such as an MDCT transform. The receiver stage may include a waveform decoding stage 240 configured to transform the first and second waveform encoded signals 201 and 202 to the time domain. The waveform decoding stage 240 generally includes an MDCT filter bank configured to perform an inverse MDCT transform of the first and second waveform encoded signals 201 and 202.

[0063] Receiver 110 further receives, in step D06, high-frequency reconstruction parameters used by high-frequency reconstruction stage 120, which is disclosed later.

[0064] The first waveform encoded signal 201 and the high-frequency parameters received by the receiver stage 110 are then input to the high-frequency reconstruction stage 120. The high-frequency reconstruction stage 120 typically operates the signal in the frequency domain, preferably in the QMF domain. Before being input to the high-frequency reconstruction stage 120, the first waveform encoded signal 201 is therefore preferably transformed to the frequency domain, preferably the QMF domain, by the QMF analysis stage 250. The QMF analysis stage 250 typically includes a QMF filter bank configured to perform a QMF transformation of the first waveform encoded signal 201.

[0065] 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 a frequency higher than the first crossover frequency f in step D08. c The frequency. Specifically, the high-frequency reconstruction stage 120 generates a frequency higher than the first crossover frequency f. c The frequency spread signal 203 contains the spectrum content of the frequency spread signal. Therefore, the frequency spread signal 203 is a high-band signal.

[0066] The high-frequency reconstruction stage 120 can operate according to any known algorithm used to perform high-frequency reconstruction. Specifically, as disclosed in the review paper 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, 2009, article ID 468971, the high-frequency reconstruction stage 120 can be configured to perform SBR. Thus, the high-frequency reconstruction stage can comprise several sub-stages configured to generate a frequency spread signal 203 in several steps. For example, the high-frequency reconstruction stage 120 can comprise a high-frequency generation stage 221, a parametric high-frequency component addition stage 222, and an envelope adjustment stage 223.

[0067] In short, in order to generate the frequency-extended signal 203, the high-frequency generation stage 221 extends the first waveform-encoded signal 201 to a frequency higher than the first crossover frequency f in the first sub-step D08a. c The frequency range. By selecting a sub-band portion of the first waveform encoded signal 201, and according to specific rules guided by high-frequency reconstruction parameters, the selected sub-band portion of the first waveform encoded signal 201 is mapped or copied to a frequency higher than the first crossover frequency f. c The selected sub-band portion of the frequency range is used to perform the generation.

[0068] The high-frequency reconstruction parameters may also include missing harmonic parameters for adding missing harmonics to the frequency spread signal 203. As discussed above, missing harmonics should be interpreted as any arbitrary strong tone portion of the spectrum. For example, missing harmonic parameters may include parameters related to the frequency and amplitude of the missing harmonics. Based on the missing harmonic parameters, the parameter high-frequency component addition stage 222 generates a sinusoidal component in sub-step D08b and adds the sinusoidal component to the frequency spread signal 203.

[0069] The high-frequency reconstruction parameters may also include spectral envelope parameters describing the target energy level of the frequency-spread signal 203. Based on the spectral envelope parameters, the envelope adjustment stage 223 may adjust the spectral content of the frequency-spread signal 203, i.e., the spectral coefficients of the frequency-spread signal 203, in sub-step D08c, so that the energy level of the frequency-spread signal 203 corresponds to the target energy level described by the spectral envelope parameters.

[0070] The frequency spread 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 generally operates in the same frequency domain, preferably the QMF domain, as the high-frequency reconstruction stage 120. Therefore, the second waveform-coded signal 202 is generally input to the interleaving stage via the QMF analysis stage 250. Furthermore, the second waveform-coded signal 202 is generally delayed by the delay stage 260 to compensate for the time taken by the high-frequency reconstruction stage 120 to perform high-frequency reconstruction. In this way, the second waveform-coded signal 202 and the frequency spread signal 203 are aligned so that the interleaving stage 130 operates on signals corresponding to the same time frame.

[0071] Then, in order to generate the interleaved signal 204, the interleaving stage 130 interleaves in step D10, that is, combines the second waveform encoded signal 202 with the frequency spread signal 203. Different methods can be used to interleave the second waveform encoded signal 202 with the frequency spread signal 203.

[0072] According to an exemplary embodiment, the interleaving stage 130 interleaves the frequency-spread signal 203 and the second waveform-encoded signal 202 by adding the frequency-spread signal 203 and the second waveform-encoded signal 202. The spectral content of the second waveform-encoded signal 202 overlaps with the spectral content of the frequency-spread signal 203 in a subset of the frequency range corresponding to the spectral content of the second waveform-encoded signal 202. By adding the frequency-spread signal 203 and the second waveform-encoded signal 202, the interleaved signal 204 thereby includes the spectral content of both the frequency-spread signal 203 and the second waveform-encoded 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, and as disclosed later, when determining the energy envelope level included in the high-frequency reconstruction parameters, the increase in the spectral envelope level due to the addition should be addressed on the encoder side. For example, the spectral envelope level for the overlapping frequencies can be reduced on the encoder side by an amount corresponding to the increase in the spectral envelope level due to the interleaving on the decoder side.

[0073] As an alternative, the increase in the spectral envelope level due to addition can be addressed on the decoder side. For example, there can be an energy measurement stage that measures the energy of the second waveform encoded signal 202, compares the measured energy with the target energy level described by the spectral envelope parameters, and adjusts the spread frequency signal 203 so that the spectral envelope level of the interleaved signal 204 is equal to the target energy level.

[0074] According to another exemplary embodiment, the interleaving stage 130 interleaves the frequency-spread signal 203 and the second waveform-coded signal 202 by replacing the spectral content of the frequency-spread signal 203 with the spectral content of the second waveform-coded signal 202 for those frequencies where the frequency-spread signal 203 and the second waveform-coded signal 202 overlap. In the exemplary embodiment where the frequency-spread signal 203 is replaced by the second waveform-coded signal 202, it is not necessary to adjust the spectral envelope level to compensate for the interleaving of the frequency-spread signal 203 and the second waveform-coded signal 202.

[0075] The high-frequency reconstruction stage 120 preferably operates at a sampling rate equal to that of the underlying core encoder used to encode the first waveform encoded signal 201. In this way, the second waveform encoded signal 202 can be encoded using the same overlapping window transform used to encode the first waveform encoded signal 201, such as the same MDCT.

[0076] The interleaving stage 130 may be further configured to preferably receive the first waveform encoded signal 201 from the receiving stage via the waveform decoding stage 240, the QMF analysis stage 250, and the delay stage 260, and to generate a combined signal 205 having spectral content at frequencies lower than and higher than the first cross frequency, the interleaving signal 204 is combined with the first waveform encoded signal 201.

[0077] The output signal from the interleaving stage 130, namely the interleaved signal 204 or the combined signal 205, can then be transformed back to the time domain by the QMF synthesis stage 270.

[0078] Preferably, the QMF analysis stage 250 and the QMF synthesis stage 270 have the same number of sub-bands, meaning that the sampling rate of the signal input to the QMF analysis stage 250 is equal to the sampling rate of the signal output from the QMF synthesis stage 270. Therefore, the waveform encoder (using MDCT) used for waveform encoding of the first and second waveform encoded signals can operate at the same sampling rate as the output signal. Thus, by using the same MDCT transformation, the first and second waveform encoded signals can be encoded efficiently and structurally easily. This differs from prior art where the sampling rate of the waveform encoder is generally limited to half the sampling rate of the output signal, and the subsequent high-frequency reconstruction module performs both upsampling and high-frequency reconstruction. This limits the ability of waveform encoding to cover the entire output frequency range.

[0079] Figure 4 An exemplary embodiment of decoder 400 is shown. Decoder 400 provides improved signal reconstruction for high frequencies in the presence of transients in the input audio signal to be reconstructed. Figure 4 Examples and Figure 2 The main difference between the examples is the spectral content and duration of the second waveform encoded signal.

[0080] Figure 4 The operation of decoder 400 in multiple subsequent time portions of a time frame is illustrated; here, three subsequent time portions are shown. A time frame may, for example, correspond to 2048 time samples. Specifically, during the first time portion, receiver 110 receives signals with frequencies up to the first cross frequency f. c1 The first waveform encoded signal 401a contains the spectrum content. The second waveform encoded signal is not received during the first time portion.

[0081] During the second time period, receiver 110 receives signals up to the first cross frequency f. c1 The first waveform encoded signal 401b of the spectrum content and having a frequency higher than the first cross frequency f c1 The second waveform encoded signal 402b corresponds to the spectral content of a subset of the frequency range. Figure 4 In the illustrated example, the second waveform encoded signal 402b has a frequency similar to the first crossover frequency f. c1 With the second cross frequency f c2 The frequency intervals extending between them correspond to the spectral content. The second waveform encoded signal 402b is thus limited to the first crossover frequency f. c1 With the second cross frequency f c2 Band-limited signals in the frequency band between.

[0082] During the third time segment, receiver 110 receives signals up to the first cross frequency f. c1 The first waveform encoded signal 401c is the spectral content. For the third time portion, the second waveform encoded signal is not received.

[0083] For the first and third time portions shown, there is no second waveform encoded signal. For these time portions, the decoder will perform conventional decoder operations, such as a conventional SBR decoder, configured to perform high-frequency reconstruction. The high-frequency reconstruction stage 120 will generate frequency spread signals 403a and 403c based on the first waveform codes 401a and 401c, respectively. However, since there is no second waveform encoded signal, the interleaving stage 130 does not perform interleaving.

[0084] For the second time portion shown, there is a second waveform encoded signal 402b. For the second time portion, the decoder 400 will use approximately... Figure 2 The same operation is described. Specifically, the high-frequency reconstruction stage 120 performs high-frequency reconstruction based on the first waveform encoded signal and high-frequency reconstruction parameters to generate a frequency-spread signal 403b. The frequency-spread signal 403b is then input to the interleaving stage 130, where it is interleaved with the second waveform encoded signal 402b to form an interleaved signal 404b. (See also...) Figure 2As discussed in the exemplary embodiments, interleaving can be performed by using addition or alternative methods.

[0085] In the examples above, there is no second waveform encoded 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. Generally, the second crossover frequency can thus change over time. In particular, the second crossover frequency can change within a time frame. Interleaving is performed when the second crossover frequency is greater than the first crossover frequency but less than the maximum frequency represented by the decoder. The case where the second crossover frequency is equal to this maximum frequency corresponds to pure waveform encoding, and high-frequency reconstruction is not required.

[0086] It should be noted that, regarding Figure 2 and Figure 4 The described embodiments can be combined. Figure 7 The diagram illustrates a time-frequency matrix 700 defined in the frequency domain, preferably the QMF domain, wherein interleaving is performed via interleaving stage 130. The illustrated time-frequency matrix 700 corresponds to a frame of the audio signal to be decoded. The illustrated matrix 700 is divided into segments starting from the first crossover frequency f. c1 The initial 16 time slots and multiple frequency sub-bands are shown. Furthermore, a first time range T1 covering time ranges below the eighth time slot, a second time range T2 covering the eighth time slot, and a time range T3 covering time slots above the eighth time slot are illustrated. Different spectral envelopes, as part of the SBR data, can be correlated with different time ranges T1 to T3.

[0087] In this example, two strong tonal components in frequency bands 710 and 720 are identified in the audio signal on the encoder side. Frequency bands 710 and 720 may have the same bandwidth as, for example, the SBR envelope band, i.e., the same frequency resolution is used to represent the spectral envelope. These tonal components in frequency bands 710 and 720 have a time range corresponding to the entire time frame, i.e., the time range of the tonal components includes time ranges T1 to T3. On the encoder side, the tonal components of waveform encoding 710 and 720 in the first time range T1 are determined, which is shown by the tonal components 710a and 720 represented by dashed lines in the first time range T1. And, on the encoder side, it is determined that in the second and third time ranges T2 and T3, the tonal components to be encoded are as follows: Figure 2The high-frequency component addition stage 222, as explained, contains a sine curve, and the first tone component 710 is parametrically reconstructed in the decoder. This is represented by a square pattern of the first tone component 710b in the second time range T2 and the third time range T3. In the second and third time ranges T2 and T3, the second tone component 720 is still waveform-encoded. Furthermore, in this embodiment, the first and second tone components are to be interleaved with the high-frequency reconstructed audio signal by addition; therefore, the encoder has adjusted the transmitted spectral envelope and SBR envelope accordingly.

[0088] Additionally, transient 730 has been identified in the audio signal on the encoder side. Transient 730 has a duration corresponding to the second time range T2, and a duration corresponding to the first crossover frequency f. c1 With the second cross frequency f c2 The frequency intervals between them correspond. The time-frequency portion of the audio signal corresponding to the waveform encoding and transient positions has been determined on the encoder side. In this embodiment, the interleaving of waveform encoding transients is accomplished by substitution. A signaling scheme is set to signal this information to the decoder. The signaling scheme includes the second waveform encoded signal in which / some time ranges and / or above the first crossover frequency f. c1 Information regarding which frequency ranges / ranges are available. The signaling scheme may also be related to rules concerning how interleaving is performed, i.e., whether interleaving is done through addition or substitution. The signaling scheme may also be related to rules, explained later, that define the priority order of adding or substituting different signals.

[0089] The signaling scheme includes a first vector 740 labeled "Additional Sine Curve," which indicates whether a sine curve should be added to the parameters for each frequency sub-band. Figure 7 In the example shown, for the corresponding subband of the first vector 740, the addition of the first tone component 710b in the second and third time ranges T2 and T3 is indicated by "1". Signaling containing the first vector 740 is known in the prior art. A rule is defined in the prior art decoder regarding when a sine curve is allowed to begin. This rule is that if a new sine curve is detected, i.e., the "another sine curve" signaling of the first vector 740 changes from 0 in one frame to 1 in the next, then for a given subband, the sine curve begins at the start of that frame, unless a transient event exists within the frame; in the case of a transient event, the sine curve begins at the transient. In the example shown, a transient event 730 exists within the frame, which explains why the parameter reconstruction using a sine curve for frequency band 710 begins only after the transient event 730.

[0090] The signaling scheme also includes a second vector 750 labeled "waveform coding". The second vector 750 indicates for each frequency sub-band whether the waveform-coded signal can be interleaved with the high-frequency reconstruction of the audio signal. Figure 7 In this example, the availability of waveform-coded signals for the corresponding sub-bands of the second vector 750, the first and second tone components 710 and 720, is indicated by a "1". In this example, the availability of waveform-coded data in the second vector 750 also indicates that interleaving should be performed by addition. However, in other embodiments, the availability of waveform-coded data in the second vector 750 may also indicate that interleaving should be performed by substitution.

[0091] The signaling scheme also includes a third vector 760 labeled "waveform coding." The third vector 760 indicates for each time slot whether the waveform-coded signal can be interleaved with the high-frequency reconstruction of the audio signal. Figure 7 In this example, for the corresponding time slot of the third vector 760, the availability of the waveform-encoded signal of the transient 730 is represented by "1". The availability representation of the waveform-encoded data in the third vector 760 also indicates that interleaving should be performed by substitution. However, in other embodiments, the availability representation of the waveform-encoded data in the third vector 760 may also indicate that interleaving should be performed by addition.

[0092] There are many alternative ways to represent the first, second, and third vectors 740, 750, and 760. In some embodiments, vectors 740, 750, and 760 are binary vectors that use logic 0 or logic 1 to provide their indication. In other embodiments, vectors 740, 750, and 760 may take different forms. For example, a first value such as "0" in the vector may indicate that no waveform-coded data is available for a particular frequency band or time slot. A second value such as "1" in the vector may indicate that interleaving is to be performed on a particular frequency band or time slot by addition. A third value such as "2" in the vector may indicate that interleaving is to be performed on a particular frequency band or time slot by substitution.

[0093] The exemplary signaling schemes described above can also be associated with a priority order that can be applied in case of conflict. As an example, a transient, interleaved third vector 760 representing an alternative mode may take precedence over the first and second vectors 740 and 750. Furthermore, the first vector 740 may take precedence over the second vector 750. It should be understood that any priority order can be defined among vectors 740, 750, and 760.

[0094] Figure 8a Show in more detail Figure 1 The interleaving stage 130 may include a signaling decoding unit 1301, a decision logic unit 1302, and an interleaving unit 1303. As discussed above, the interleaving stage 130 receives a second waveform encoded signal 802 and a frequency spread signal 803. The interleaving stage 130 may also receive a control signal 805. The signaling decoding unit 1301 decodes the control signal 805 into a signal that is analogous to a reference signal. Figure 7The described signaling scheme comprises three parts: a first vector 740, a second vector 750, and a third vector 760. These are sent to a decision logic unit 1302, which, based on logic, creates a time / frequency matrix 870 for QMF frames, indicating which of the second waveform encoded signal 802 and the frequency spread signal 803 should be used for which time / frequency segment. The time / frequency matrix 870 is sent to an interleaving unit 1303 and is used when interleaving the second waveform encoded signal 802 with the frequency spread signal 803.

[0095] exist Figure 8b The decision logic unit 1302 is shown in more detail below. The decision logic unit 1302 may include a time / frequency matrix generation unit 13021 and a priority ordering unit 13022. The time / frequency generation unit 13021 generates a time / frequency matrix 870 having time / frequency segments corresponding to the current QMF frame. The time / frequency generation unit 13021 incorporates information from a first vector 740, a second vector 750, and a third vector 760 into the time / frequency matrix. For example, as... Figure 7 As shown, if a "1" exists in the second vector 750 for a certain frequency (or, more generally, any value other than zero), then in the time / frequency matrix 870, the time / frequency segment corresponding to that frequency is set to "1" (or, more generally, set to a value present in vector 750), indicating that interleaving with the second waveform encoded signal 802 is to be performed on these time / frequency segments. Similarly, if a "1" exists in the third vector 760 for a certain time slot (or, more generally, any value other than zero), then in the time / frequency matrix 870, the time / frequency segment corresponding to that time slot is set to "1" (or, more generally, set to any value other than zero), indicating that interleaving with the second waveform encoded signal 802 is to be performed on these time / frequency segments. Similarly, if there is a "1" in the first vector 740 for a certain frequency, then in the time / frequency matrix 870, the time / frequency segment corresponding to that frequency is set to "1", indicating that the output signal 804 is to be based on the frequency extension signal 803 that has been reconstructed in terms of parameters, for example, by including a sine wave signal.

[0096] For some time / frequency segments, there are conflicts between the information from the first vector 740, the second vector 750, and the third vector 760. This means that for the same time / frequency segment in the time / frequency matrix 870, more than one vector in vectors 740-760 represents a value different from zero, such as "1". In this case, to eliminate the conflicts in the time / frequency matrix 870, the priority ordering unit 13022 needs to determine how to prioritize the information from the vectors. More precisely, the priority ordering unit 13022 determines whether the output signal 804 is based on the frequency spread signal 803 (thus giving priority to the first vector 740), or through the interleaving of the second waveform encoded signal 802 in the frequency direction (thus giving priority to the second vector 750), or through the interleaving of the second waveform encoded signal 802 in the time direction (thus giving priority to the third vector 760).

[0097] For this purpose, the priority ordering component 13022 includes predetermined rules relating to the priority order of vectors 740-760. The priority ordering component 13022 may also include predetermined rules relating to how to perform interleaving, i.e., whether to perform interleaving by adding or substituting.

[0098] Preferably, these rules are as follows:

[0099] • Interleaving in the time direction, i.e., interleaving defined by the third vector 760, is given the highest priority. Preferably, interleaving in the time direction is performed by replacing the frequency spread signal 803 in those time / frequency segments defined by the third vector 760. The time resolution of the third vector 760 corresponds to the time slot of the QMF frame. If the QMF frame corresponds to 2048 time-domain samples, then the time slot can generally correspond to 128 time-domain samples.

[0100] • Frequency parameter reconstruction, i.e., the frequency spread signal 803 defined by the first vector 740 is given second-highest priority. The frequency resolution of the first vector 740 is, for example, the frequency resolution of a QMF frame in an SBR envelope. Existing technical rules relating to signaling and interpretation of the first vector 740 remain in effect.

[0101] • Frequency direction interleaving, i.e., the interleaving defined by the second vector 750, is given the lowest priority. Frequency direction interleaving is performed by adding a frequency spread signal 803 to those time / frequency segments defined by the second vector 750. The frequency resolution of the second vector 750 corresponds to the frequency resolution of a QMF frame, such as an SBR envelope.

[0102] III. Exemplary Example – Encoder

[0103] Figure 5An exemplary embodiment of an encoder 500 suitable for an audio processing system is shown. The encoder 500 includes a receiving stage 510, a waveform encoding stage 520, a high-frequency encoding stage 530, an interleaving code detection stage 540, and a transmission stage 550. The high-frequency encoding stage 530 may include a high-frequency reconstruction parameter calculation stage 530a and a high-frequency reconstruction parameter adjustment stage 530b.

[0104] The following is for reference Figure 5 and Figure 6 The flowchart describes the operation of encoder 500. In step E02, receiver 510 receives the audio signal to be encoded.

[0105] The received audio signal is input to the high-frequency coding stage 530. Based on the received audio signal, the high-frequency coding stage 530, particularly the high-frequency reconstruction parameter calculation stage 530a, calculates in step E04 that a frequency higher than the first crossover frequency f can be achieved. c The high-frequency reconstruction parameters of the received audio signal are calculated. The high-frequency reconstruction parameter calculation stage 530a can use any known technique for calculating the high-frequency reconstruction parameters, such as SBR coding. The high-frequency coding stage 530 generally operates in the QMF domain. Therefore, before calculating the high-frequency reconstruction parameters, the high-frequency coding stage 530 can perform QMF analysis of the received audio signal. As a result, the high-frequency reconstruction parameters are defined with respect to the QMF domain.

[0106] The calculated high-frequency reconstruction parameters may include several parameters related to high-frequency reconstruction. For example, the high-frequency reconstruction parameters may include parameters related to how to reconstruct frequencies from frequencies below the first crossover frequency f. c The audio signal of the sub-band portion of the frequency range is mapped or copied to a frequency higher than the first cross frequency f. c The parameters are related to the sub-band portion of the frequency range. These parameters are sometimes referred to as parameters describing the patching structure.

[0107] The high-frequency reconstruction parameters may also include spectral envelope parameters that describe the target energy level in the sub-band portion of the frequency range above the first crossover frequency.

[0108] The high-frequency reconstruction parameters may also include missing harmonic parameters indicating the harmonics, or missing strong tone components if the audio signal is reconstructed in a frequency range above the first cross frequency using parameters describing the patch structure.

[0109] Interleaved coding detection level 540 then identifies, in step E06, the spectral content of the received audio signal to be waveform-coded above the first crossover frequency f. c A subset of the frequency range. In other words, the role of the interleaved coding detection level 540 is to identify frequencies above the first crossover frequency (for which high-frequency reconstruction cannot yield the desired results).

[0110] The interleaved coding detection level 540 can employ different methods to identify frequencies above the first crossover frequency f. c The frequency range is a relevant subset. For example, the interleaved coding detection stage 540 can identify strong tone components that cannot be well reconstructed through high-frequency reconstruction. The identification of strong tone components can be based on the received audio signal, for example, by determining the energy of the audio signal according to its frequency and identifying frequencies with high energy as containing strong tone components. Furthermore, the identification can be based on knowledge of how the decoder reconstructs the received audio signal. In particular, this identification can be based on a tone quota, which is the ratio of the tone measure of the received audio signal to the reconstructed tone measure of the received audio signal in a frequency band above the first cross frequency. A high tone quota indicates that the audio signal will not be well reconstructed for frequencies corresponding to the tone quota.

[0111] The interleaving-coded detection stage 540 can also detect transients in the received audio signal that cannot be well reconstructed through high-frequency reconstruction. This identification can be the result of time-frequency analysis of the received audio signal. For example, the time-frequency intervals in which transients occur can be detected from the spectrogram of the received audio signal. These time-frequency intervals generally have a shorter time range than the time frame of the received audio signal. The corresponding frequency range generally corresponds to a frequency interval extending to the second cross frequency. A subset of the frequency range above the first cross frequency can therefore be identified by the interleaving-coded detection stage 540 as intervals extending from the first cross frequency to the second cross frequency.

[0112] The interleaving coding detection stage 540 can also 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 interleaving coding detection stage 540 can identify the frequency of the missing harmonic and determine the frequency above the first crossover frequency f. c The identified subset of the frequency range contains at least some of the frequencies of the missing harmonics. This approach may be advantageous if strong tonal components exist in an audio signal that cannot be correctly modeled within the limits of the parametric model.

[0113] The received audio signal is also input to waveform encoding stage 520. Waveform encoding stage 520 performs waveform encoding of the received audio signal in step E08. Specifically, waveform encoding stage 520 encodes the waveform up to the first cross frequency f. c The audio signal in the frequency band is used to generate a first waveform encoded signal. Furthermore, waveform encoding stage 520 receives the identified subset from interleaved encoding detection stage 540. Waveform encoding stage 520 then generates a second waveform encoded signal by waveform encoding the received audio signal in the frequency band corresponding to the identified subset in the frequency range above the first cross frequency. The second waveform encoded signal will thus have a frequency band above the first cross frequency f. cThe frequency range of the identified subset corresponds to the spectral content.

[0114] According to an exemplary embodiment, waveform coding stage 520 can generate first and second waveform coded signals by first waveform coding the received audio signal across all spectral bands, and then coding the signal with frequencies higher than the first crossover frequency f. c The frequency of the identified subset of frequencies is removed to extract the spectral content of the waveform-encoded signal.

[0115] The waveform coding stage can perform waveform coding, for example, by using an overlapping window transform filter bank such as an MDCT filter bank. This overlapping window transform filter bank uses a window with a certain time length, such that the value of the transformed signal in one time frame is affected by the values ​​of the signal in the preceding and following time frames. To reduce this effect, it may be advantageous to perform a certain amount of time overcoding, meaning that waveform coding stage 520 not only waveform codes the current time frame of the received audio signal, but also waveform codes the preceding and following time frames of the received audio signal. Similarly, high-frequency coding stage 530 can also encode not only the current time frame of the received audio signal, but also the preceding and following time frames of the received audio signal. In this way, cross-fading between the second waveform-coded signal and the high-frequency reconstruction of the audio signal can be improved in the QMF domain. Furthermore, this reduces the need for adjustments to the spectral envelope data boundaries.

[0116] It should be noted that the first and second waveform encoded signals can also be separate signals. However, preferably, they form the first and second waveform encoded signal portions of a common signal. If so, they can be generated by performing a single waveform encoding operation on the received audio signal, such as applying a single MDCT transform to the received audio signal.

[0117] The high-frequency coding stage 530, particularly the high-frequency reconstruction parameter adjustment stage 530b, can also receive the identified subset of frequencies above the first crossover frequency fc. Based on the received data, the high-frequency reconstruction parameter adjustment stage 530b can adjust the high-frequency reconstruction parameters in step E10. Specifically, the high-frequency reconstruction parameter adjustment stage 530b can adjust the high-frequency reconstruction parameters corresponding to the spectral bands contained in the identified subset.

[0118] For example, the high-frequency reconstruction parameter adjustment stage 530b can adjust the spectral envelope parameters of the target energy level describing the sub-band portion of the frequency range above the first crossover frequency. This is particularly relevant if a second waveform encoded signal is added to the high-frequency reconstruction of the audio signal in the decoder, because the energy of the second waveform encoded signal will be added to the energy of the high-frequency reconstruction. To compensate for this addition, the high-frequency reconstruction parameter adjustment stage 530b can adjust the spectral envelope parameters of the sub-band portion of the frequency range above the first crossover frequency f. cThe energy envelope parameter is adjusted by subtracting the measured energy of the second waveform-coded signal from the target energy level using the spectral band corresponding to the identified subset of the frequency range. In this way, the total signal energy is preserved when the second waveform-coded signal is added to the decoder and high-frequency reconstruction is performed. The energy of the second waveform-coded signal can be measured, for example, by the interleaved coding detection stage 540.

[0119] The high-frequency reconstruction parameter adjustment stage 530b can also adjust the missing harmonic parameters. More specifically, if the subband containing the missing harmonic represented by the missing harmonic parameters is above the first crossover frequency f... c If a subband is identified as part of the frequency range, then that subband will be waveform encoded by waveform encoding stage 520. Therefore, high-frequency reconstruction parameter adjustment stage 530b can remove such missing harmonics from the missing harmonic parameters because such missing harmonics do not need to be reconstructed by parameters on the decoder side.

[0120] The transport 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 transport stage 550 formats the received data into a bitstream for transmission to the decoder.

[0121] The interleaving code detection stage 540 can also signal information to the transport stage 550 so that it is included in the bit stream. Specifically, the interleaving code detection stage 540 signals how to reconstruct the interleaved second waveform coded signal using the high frequencies of the audio signal (e.g., whether interleaving is performed by adding signals or by replacing one signal with another), and for what frequency range and time interval the waveform coded signal should be interleaved. For example, this can be achieved by using a reference... Figure 7 The signaling scheme discussed will be implemented.

[0122] Equivalents, extensions, substitutions, and hybrids

[0123] After studying the above description, those skilled in the art will be able to conceive of other embodiments of this disclosure. Although embodiments and examples have been disclosed in this specification and accompanying drawings, this disclosure is not limited to these specific examples. Numerous modifications and variations may be made without departing from the scope of this disclosure as defined by the appended claims. Any reference numerals appearing in the claims should not be construed as limiting their scope.

[0124] Furthermore, by studying the accompanying drawings, this disclosure, and the appended claims, those skilled in the art who practice this disclosure can understand and implement variations of the disclosed embodiments. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite articles "a" or "an" do not exclude multiple. The mere recitation of certain measures in several different dependent claims does not imply that a combination of these measures cannot be fully utilized.

[0125] The systems and methods disclosed above can be implemented as software, firmware, hardware, or a combination thereof. In hardware implementation, the division of tasks among the functional units mentioned in the above description does not necessarily correspond to the division of multiple units; instead, a physical component may have multiple functions, and a task may be implemented by several cooperating physical components. Some or all of the components may be implemented as software executed by a digital signal processor or microprocessor, or as hardware or application-specific integrated circuits. Such software may be distributed on a computer-readable medium that may contain computer storage media (or non-transitory media) or communication media (or transient media). As is known to those skilled in the art, the term computer storage medium includes volatile and non-volatile, removable and non-removable media implemented in any method or technology for storing information such as computer-readable instructions, data structures, program modules, or other data. Computer storage media include, but are not limited to, RAM, ROM, EEPROM, rewritable flash memory or other memory technologies, CD-ROM, digital universal disc (DVD) or other optical disc storage, magnetic cartridges, magnetic tape, disk storage or other magnetic storage devices, or any other medium that can be used to store desired information and is accessible by a computer. Furthermore, as is known to those skilled in the art, communication media generally embody computer-readable instructions, data structures, program modules, or other data in modulated data signals such as carrier waves or other transmission mechanisms, and include any information transmission medium.

Claims

1. A method for decoding audio signals in an audio processing system, comprising: Receive a first waveform-coded signal that includes spectral content up to the first cross frequency; Receive a second waveform-coded signal that includes spectral content corresponding to a subset of frequencies above the first cross frequency; Receive high-frequency reconfiguration parameters; as well as High-frequency reconstruction is performed by using at least a portion of a first waveform coded signal and high-frequency reconstruction parameters to generate a frequency-spread signal with spectral content higher than a first crossover frequency, wherein the high-frequency reconstruction includes adjusting the energy level of the sub-bands of the frequency-spread signal based on a target energy level of the sub-bands of the frequency-spread signal.

2. The method according to claim 1, wherein, The spectral content of the second waveform coded signal overlaps with the spectral content of the frequency spread signal in a subset of the frequency range above the first cross frequency.

3. The method according to claim 1, wherein, Adjusting the energy level of the subband of the frequency spread signal includes subtracting the energy level of the subband of the frequency spread signal from the target energy level of the subband.

4. The method according to claim 1, wherein, Performing high-frequency reconstruction involves copying lower frequency bands to higher frequency bands.

5. The method according to claim 1, further comprising adjusting the spectral content of the frequency spread signal according to the high-frequency reconstruction parameters, so as to adjust the spectral envelope of the frequency spread signal.

6. A non-transitory computer-readable storage medium storing instructions that, when executed by a processor, cause the processor to perform the method according to any one of claims 1-5.

7. An apparatus for decoding coded audio signals, comprising: The input interface is configured to receive a first waveform-coded signal comprising spectral content up to a first cross frequency, and a second waveform-coded signal comprising spectral content corresponding to a subset of frequencies above the first cross frequency. as well as A high-frequency reconstructor is configured to receive a first waveform-encoded signal and high-frequency reconstruction parameters from the input interface, and to perform high-frequency reconstruction using the first waveform-encoded signal and the high-frequency reconstruction parameters to generate a frequency-spread signal with spectral content higher than a first crossover frequency, wherein the high-frequency reconstruction includes adjusting the energy level of the sub-bands of the frequency-spread signal based on a target energy level of the sub-bands of the frequency-spread signal.

8. An apparatus for decoding an encoded audio signal, comprising components for performing the method according to any one of claims 1-5.

9. An apparatus for decoding encoded audio signals, comprising: At least one processor, and A non-transitory computer-readable storage medium comprising executable instructions that, when executed by at least one processor, cause at least one processor to perform the method according to any one of claims 1-5.

10. A computer program product having instructions that, when executed by a computing device or system, cause the computing device or system to perform the method according to any one of claims 1-5.

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