EA044947B1 - BACKWARD COMPATIBLE HARMONIC TRANSPOSER LAYOUT FOR RECONSTRUCTION OF HIGH FREQUENCY AUDIO SIGNALS - Google Patents

Description

Field of technology to which the invention relates

Embodiments relate to processing audio signals, and more specifically, encoding, decoding or recoding audio bitstreams with control data specifying whether a basic form of high frequency reconstruction (HFR) or an advanced form of HFR is to be performed on the audio data.

BACKGROUND OF THE INVENTION

A typical audio bitstream includes both audio data (eg, encoded audio data) indicating one or more channels of audio content, and metadata indicating at least one characteristic of the audio data or audio content. One well-known format for generating an encoded audio bitstream is the MPEG-4 Advanced Audio Coding (AAC) format described in the ISO/IEC 14496-3:2009 MPEG standard. In the MPEG-4 standard, AAC stands for Advanced Audio Coding and HE-AAC stands for High Efficiency Advanced Audio Coding.

The AAC MPEG-4 standard defines several audio profiles that determine what objects and encoding tools are present in a compatible encoder or decoder. Three of these audio profiles are (1) AAC profile, (2) HE-AAC profile and (3) HE-AAC v2 profile. The AAC profile includes the AAC Low Complexity (or AAC-LC) object type. The AAC-LC object is the analogue of the MPEG-2 low complexity AAC profile with some adjustments and does not include either a spectrum band replication (SBR) object type or a parametric stereo (PS) object type. The HE-AAC profile is a superset of the AAC profile and additionally includes an SBR object type. The HE-AAC v2 profile is a superset of the HE-AAC profile and additionally includes a PS object type.

The SBR object type contains a spectrum band replication facility, which is an important high-frequency reconstruction (HFR) encoding facility that significantly improves the compression efficiency of perceptual audio codecs. SBR reconstructs the high-frequency components of the audio signal at the receiver end (for example, at the decoder). Thus, the encoder only needs to encode and transmit low-frequency components, providing the opportunity for much higher audio quality at low data rates. SBR is based on replication of harmonic sequences, previously truncated to reduce the data rate, from the available bandwidth-limited signal and control data received from the encoder. The relationship between tonal and noise-like components is maintained through adaptive inverse filtering, as well as the optional addition of noise and sine waves. In the MPEG-4 AAC standard, the SBR facility performs spectral pasting (also called linear transform or spectral transform) in which a number of successive quadrature mirror filter (QMF) subbands are copied (or pasted) from the transmitted portion of the low-pass band. audio signal into the part of the high frequency band of the audio signal, which is generated in the decoder.

Spectral pasting or linear mapping may not be ideal for some types of audio signal, such as music content with relatively low crossover frequencies. Therefore, technologies are needed to improve the replication of spectrum bands.

Brief Description of Embodiments of the Invention

A first group of embodiments is disclosed, which relates to a method for decoding an encoded audio bitstream. The method includes receiving an encoded audio bitstream and decoding the audio data to generate a decoded low-band audio signal. The method further includes extracting high-pass reconstruction metadata and filtering the decoded low-band audio signal with a signal decomposition filter bank to generate a filtered low-band audio signal. The method further includes extracting a flag indicating whether spectral transform or harmonic transposition should be performed on the audio data, and reconstructing the high-frequency portion of the audio signal using the low-band filtered audio signal and high-pass reconstruction metadata in accordance with the flag. Finally, the method includes combining a filtered low-band audio signal and a reconstructed high-band portion to generate a wideband audio signal.

A second group of embodiments relates to an audio decoder for decoding an encoded audio bitstream. The decoder includes an input interface for receiving a coded audio bitstream, where the coded audio bitstream includes audio data representing a low frequency portion of the audio signal, and a main decoder for decoding the audio data to generate a decoded audio signal in the low frequency band. The decoder also includes a demultiplexer for extracting high frequency reconstruction metadata from the encoded audio bitstream, where the high frequency reconstruction metadata

- 1 044947 frequencies include operating parameters for a high-frequency reconstruction process that linearly converts a number of successive subbands from the low-band portion of the audio signal to the high-band portion of the audio signal, and a signal decomposition filter bank for filtering the decoded audio signal in the low frequency band to generate a filtered audio signal in the low frequency band. The decoder further includes a demultiplexer for extracting from the encoded audio bit stream a flag indicating whether linear transform or harmonic transposition is to be performed on the audio data, and a high-pass restorer for restoring the high-frequency portion of the audio signal using the low-band filtered audio signal. and high-frequency reconstruction metadata according to the flag. Finally, the decoder includes a signal synthesis filter bank for combining the filtered low-band audio signal and the reconstructed high-band portion to generate a wideband audio signal.

Other groups of embodiments relate to encoding and recoding audio bitstreams containing metadata identifying whether enhanced spectrum band replication (eSBR) processing is to be performed.

Brief description of drawings

Fig. 1 is a block diagram of an embodiment of a system that may be configured to perform an embodiment of the inventive method.

Fig. 2 is a block diagram of an encoder, which is an embodiment of an inventive audio signal processing unit.

Fig. 3 is a block diagram of a system including a decoder, which is an embodiment of an inventive audio signal processing unit, and optionally also a post-processor coupled thereto.

Fig. 4 is a block diagram of a decoder, which is an embodiment of an inventive audio signal processing unit.

Fig. 5 is a block diagram of a decoder, which is another embodiment of an inventive audio signal processing unit.

Fig. 6 is a block diagram of another embodiment of an inventive audio signal processing unit.

Fig. 7 is a diagram of an MPEG-4 AAC bitstream block including the segments into which it is divided.

Notation system and terminology

Throughout this specification, including in the claims, the expression performing an operation on a signal or data (e.g., filtering, scaling, transforming, or applying a gain to a signal or data) is used broadly to mean performing an operation directly on a signal or data. data, or on a processed version of the signal or data (for example, on a version of the signal that has been pre-filtered or pre-processed before performing an operation on it).

Throughout this specification, including in the claims, the expression audio signal processing unit or audio processor is used in a broad sense to refer to a system, device or installation configured to process audio data. Examples of audio signal processing units include, but are not limited to, encoders, transcoders, decoders, codecs, pre-processing systems, post-processing systems, and bitstream processing systems (sometimes referred to as bitstream processing means). Almost all consumer electronics, such as mobile phones, televisions, travel computers, tablet computers, contain an audio signal processing unit or sound processor.

Throughout this specification, including in the claims, the term attached or attached is used in a broad sense to mean direct or indirect connection. Thus, if a first device is connected to a second device, the connection may occur through a direct connection or through an indirect connection via other devices and connections. Moreover, components that are combined into or with other components are also connected to each other.

Detailed Description of Embodiments of the Invention

The AAC MPEG-4 standard assumes that an AAC MPEG-4 encoded bitstream includes metadata indicating each type of high frequency reconstruction (HFR) processing that must be performed, if any, by the decoder to decode the audio content of the bitstream. and/or which controls such HFR processing and/or indicates at least one characteristic or parameter of at least one HFR means to be used for decoding the audio content of the bitstream. Throughout this application, we use the expression SBR metadata to refer to metadata of this type, which is described or

- 2 044947 is mentioned in the AAC MPEG-4 standard for use with spectrum band replication (SBR). As will be appreciated by one skilled in the art, SBR is a type of HFR.

SBR is preferably used as a double sample rate system, with the underlying codec running at half the original sample rate, while SBR. operates at the original sampling rate. The SBR encoder runs in parallel with the underlying main codec, albeit at a higher sample rate. Although SBR. is primarily post-processed in the decoder, important parameters are extracted in the encoder in order to provide the most accurate high-frequency reconstruction in the decoder. The encoder estimates the spectral envelope of the SBR band, which relates to the time-frequency range/time and frequency resolution appropriate to the characteristics of the current segments of the input signal. The spectral envelope is estimated by decomposing the signal using complex QFTs and subsequent energy calculations. The time and frequency resolutions of the spectral envelopes can be selected with a high degree of freedom to provide the best time and frequency resolution for a given input signal segment. Envelope estimation must take into account that the transient in the original, primarily located in the high frequency region (e.g., high overshoot), will be present to a minor extent in the SBR generated high frequency band before envelope correction, since the high frequency band in the decoder is based on the low frequency band frequencies, where the transient process is expressed to a much lesser extent compared to the high frequency band. This aspect places different requirements on the time and frequency resolution of the spectral envelope data compared to traditional spectral envelope estimation as used in other audio coding algorithms.

In addition to the spectrum envelope, several additional parameters are extracted, representing the spectral characteristics of the input signal for different time-frequency domains. Since the encoder naturally has access to the original signal, as well as information about how the SBR block in the decoder will produce the high frequency band, subject to a certain set of control parameters, it is possible for the system to cope with situations where the low frequency band constitutes a powerful harmonic series, and the high frequency band that must be recreated consists mainly of random components of the signal, as well as situations where strong tonal components are present in the original high frequency band without analogues in the low frequency band on which the high frequency band region is based. Moreover, the SBR encoder works closely with the underlying host codec to estimate which frequency range should be covered by SBR at a given time. SBR data is intelligently encoded before transmission using entropy encoding as well as control data channel dependencies in the case of stereo signals.

Control parameter extraction algorithms typically need to be carefully tuned to the underlying codec at a given bit rate and a given sample rate. This is due to the fact that lower bitrates typically rely on a larger SBR range compared to high bitrates, and different sampling rates correspond to different time resolutions of SBR frames.

An SBR decoder typically includes several different parts. It contains a bitstream decoding module, a high-frequency recovery (HFR) module, an additional high-frequency component module, and an envelope corrector module. The system is based on a filter bank of complex-valued FQFs. In the bitstream extracting module, control data is read from the bitstream and decoded. The time/frequency grid is obtained for the current frame before reading the envelope data from the bitstream. The underlying main decoder decodes the current frame's audio signal (albeit at a lower sampling rate) to produce time-domain audio samples. The resulting audio data frame is used for high frequency reconstruction by the HFR module. The decoded low-band signal is then subjected to signal decomposition using a FQF filter bank. Reconstruction of high frequencies and correction of the envelope are subsequently performed on samples of the sub-bands of the filter bank from the FQF. High frequencies are reconstructed from the low frequency band in a flexible manner based on specified control parameters. Moreover, the reconstructed high frequency band is adaptively filtered based on the subband channels according to the control data to ensure proper spectral characteristics of a given frequency/time domain.

The top layer of an MPEG-4 AAC bitstream is a sequence of data blocks (raw_data_block elements), each of which is a data segment (referred to herein as a block) that contains audio data (typically for a period of time of 1024 or 960 samples) and related information and/or other data. As used herein, we use the term block to refer to a segment of an MPEG-4 AAC bitstream containing audio data (and associated metadata and, optionally, also other associated data) that defines or is indicative of one (but not more than one) element raw_data_block.

Each MPEG-4 AAC bitstream block may include a number of syntax elements (each of which is also materialized in the bitstream as a data segment). Seven types of such syntax elements are defined in the MPEG-4 AAC standard. Each syntax element is identified by a different id_syn_ele data element value. Examples of syntax elements include single_channel_element(), channel_pair_element(), and fill_element(). A single channel element is a container including audio data of a single audio channel (monaural audio signal). A channel pair element includes audio data of two audio channels (ie, a stereo audio signal).

A padding element is a container of information including an identifier (eg, the value of the id_syn_ele element noted above) followed by data that is referred to as padding data. Padding elements have historically been used to correct the instantaneous bit rate of bit streams that must be transmitted over a constant bit rate channel. By adding an appropriate amount of padding data to each block, a constant data transfer rate can be achieved.

In accordance with embodiments of the invention, the padding data may include one or more extension payloads that extend the type of data (eg, metadata) that can be transmitted in the bit stream. A decoder that receives bitstreams with padding data containing a new data type can optionally be used by a device receiving the bitstream (eg, a decoder) to enhance the functionality of the device. Thus, as may be appreciated by one of ordinary skill in the art, padding is a special type of data structure and is different from the data structures typically used to transmit audio data (eg, audio payloads containing channel data).

In some embodiments of the invention, the identifier used to identify the padding element may consist of a three-bit unsigned most significant bit first (uimsbf) integer having the value 0x6. Multiple instances of the same type of syntactic element (for example, multiple pad elements) may appear in the same block.

Another standard for encoding audio bitstreams is the Unified Speech and Audio Coding (USAC) MPEG standard (ISO/IEC 23003-3:2012). The USAC MPEG standard describes the encoding and decoding of audio content using spectrum replication processing (including SBR processing as described in the AAC MPEG-4 standard, and also including other advanced forms of spectrum replication processing). This processing employs spectrum band replication facilities (sometimes referred to herein as enhanced SBR facilities or eSBR facilities) of an extended and enhanced version of the SBR feature set described in the MPEG-4 AAC standard. Thus, eSBR (as defined in the USAC standard) is an improvement over SBR (as defined in the AAC MPEG-4 standard).

As used herein, we use the expression enhanced SBR processing (or eSBR processing) to refer to spectrum band replication processing using at least one eSBR facility (e.g., at least one eSBR facility that is described or referenced in the USAC MPEG standard), which is not described or mentioned in the MPEG-4 AAC standard. Examples of such eSBR features are harmonic transposition and additional pre-processing of the paste using QZF or pre-alignment.

An integer-order harmonic transposer T maps a sine wave of frequency co into a sine wave of frequency Tco, while maintaining the duration of the signal. Three orders, T=2, 3, 4, are typically used sequentially to create each portion of the desired output frequency range using the smallest possible transposition order. If an output signal above the fourth order transposition range is required, it can be generated by frequency shifts. Whenever possible, near-critically sampled baseband time regions are created for processing to minimize computational complexity.

A bitstream generated in accordance with the USAC MPEG standard (sometimes referred to herein as a USAC bitstream) includes encoded audio content and typically includes metadata indicating each type of spectrum band replication processing to be applied by the decoder for decoding USAC bitstream audio content, and/or metadata that controls such spectrum band replication processing or indicates at least one characteristic or parameter of at least one SBR means and/or eSBR means that is to be used to decode the USAC bitstream audio content.

As used herein, we use the expression enhanced SBR metadata (or eSBR metadata) to refer to metadata indicating each type of spectrum band replication processing to be applied by a decoder to decode the audio content of an encoded audio bitstream (e.g., a USAC bitstream), and/or which control such spectrum band replication processing and/or indicate at least one characteristic or

- 4 044947 parameter of at least one SBR means and/or eSBR means to be used for decoding such audio content, but which are not described or mentioned in the MPEG-4 AAC standard. An example of eSBR metadata is metadata (indicating or intended to control spectrum band replication processing) that is described or referenced in the USAC MPEG standard, but not in the AAC MPEG-4 standard. Thus, eSBR metadata as used herein refers to metadata that is not SBR metadata, and SBR metadata as used herein refers to metadata that is not eSBR metadata.

The USAC bitstream may include both SBR metadata and eSBR metadata. More specifically, the USAC bitstream may include eSBR metadata that controls the execution of eSBR processing by the decoder, and SBR metadata that controls the execution of SBR processing by the decoder. In accordance with exemplary embodiments of the present invention, eSBR metadata (eg, eSBR-specific configuration data) (in accordance with the present invention) is included in the MPEG-4 AAC bitstream (eg, in the sbr_extension() container at the end of the SBR payload).

Performing eSBR processing while decoding an encoded bitstream using an eSBR engine (comprising at least one eSBR engine) installed by the decoder restores the high frequency band of the audio signal based on the replication of harmonic sequences that were truncated during encoding. Such eSBR processing typically adjusts the spectral envelope of the generated high-pass band and applies inverse filtering, and adds noise and sine components to recreate the spectral characteristics of the original audio signal.

In accordance with exemplary embodiments of the invention, eSBR metadata is included (e.g., a small number of control bits that are eSBR metadata is included) in one or more metadata segments of an encoded audio bitstream (e.g., an MPEG-4 AAC bitstream) that also includes encoded audio data in other segments (audio data segments). Typically, at least one such metadata segment of each bitstream block is (or includes) a padding element (including an identifier indicating the start of the padding element), and the eSBR metadata is included in the padding element after the identifier. Fig. 1 is a block diagram of an exemplary audio signal processing circuit (audio data processing system) in which one or more elements of the system may be implemented in accordance with an embodiment of the present invention. The system includes the following elements connected to each other as shown: an encoder 1, a delivery subsystem 2, a decoder 3 and a post-processing unit 4. In variations of the system shown, one or more elements are not included, or additional audio processing units are included.

In some implementations, encoder 1 (which optionally includes a pre-processing unit) is configured to receive PCM (time domain) samples containing audio content as an input signal and output an encoded audio bitstream (having a format that is compatible with the standard AAC MPEG-4), which is indicative of audio content. Bitstream data that indicates audio content is sometimes referred to herein as audio data or encoded audio data. If the encoder is implemented in accordance with an exemplary embodiment of the present invention, the audio bitstream output from the encoder includes eSBR metadata (and typically other metadata as well) as well as audio data.

One or more coded audio streams output from the encoder 1 may be presented to the coded audio delivery subsystem 2. Subsystem 2 is configured to store and/or deliver each encoded bitstream output from encoder 1. The encoded audio bitstream output from encoder 1 may be stored by subsystem 2 (eg, as a DVD or Bluray disc) or transmitted by subsystem 2 (which may implement a channel or transmission network), or may be both stored and transmitted by subsystem 2.

Decoder 3 is configured to decode an AAC MPEG-4 encoded audio bitstream (generated by encoder 1) that it receives via subsystem 2. In some embodiments, decoder 3 is configured to extract eSBR metadata from each block of the bitstream and decode the bitstream ( including by performing eSBR processing using the extracted eSBR metadata) to generate decoded audio data (eg, streams of decoded PCM audio samples). In some embodiments, decoder 3 is configured to extract SBR metadata from the bitstream (but ignore eSBR metadata included in the bitstream) and decode the bitstream (including by performing SBR processing using the extracted SBR metadata) to generate decoded audio data (e.g., streams of decoded samples of the PCM audio signal. Typically, decoder 3 includes a buffer that stores (e.g., in a non-ephemeral manner) segments of the encoded audio bitstream received from subsystem 2.

- 5 044947

Post-processing block 4 according to FIG. 1 is configured to receive a stream of decoded audio data from the decoder 3 (eg, samples of a PCM audio signal) and perform post-processing on it. The post-processing unit may also be configured to reproduce the post-processed audio content (or the decoded audio signal received from the decoder 3) for playback by one or more speakers.

Fig. 2 is a block diagram of an encoder (100), which is an embodiment of an inventive audio signal processing unit. Any of the components or elements of encoder 100 may be implemented as one or more processes and/or one or more circuits (e.g., ASICs, FPGAs, or other integrated circuits) in hardware, software software or combination of hardware and software. Encoder 100 includes an encoder 105, a filler/formatter stage 107, a metadata generation stage 106, and a buffer memory 109 connected as shown. In addition, typically, encoder 100 includes other processing elements (not shown). Encoder 100 is configured to convert an input audio bitstream into an encoded MPEG-4 AAC output bitstream.

A metadata generator 106 is coupled to and configured to generate (and/or pass through cascade 107) metadata (including eSBR metadata and SBR metadata) to be included by cascade 107 in an encoded bitstream to be output from encoder 100.

An encoder 105 is coupled and configured to encode (e.g., by performing compression on it) the input audio data and present the resulting encoded audio signal to stage 107 for inclusion in a coded bitstream to be output from stage 107.

Stage 107 is configured to multiplex a coded audio signal from encoder 105 and metadata (including eSBR metadata and SBR metadata) from generator 106 to form a coded bit stream to be output from stage 107, preferably such that the coded bit stream has the format , as defined by one embodiment of the present invention.

Buffer memory 109 is configured to store (for example, in a non-ephemeral manner) at least one block of encoded audio bitstream output from stage 107, and the sequence of blocks of encoded audio bitstream is then presented from buffer memory 109 as an output from encoder 100 to the system. delivery.

Fig. 3 is a block diagram of a system including a decoder (200), which is an embodiment of an inventive audio signal processing unit, and optionally also a post-processor (300) coupled thereto. Any of the components or elements of the decoder 200 and post-processor 300 may be implemented as one or more processes and/or one or more circuits (eg, ASICs, FPGAs, or other integrated circuits) in hardware hardware, software or a combination of hardware and software. Decoder 200 includes a buffer memory 201, a bitstream payload deformer 205, an audio decoding subsystem 202 (sometimes referred to as a main decoding stage or main decoding subsystem), an eSBR processing stage 203, and a control bit generation stage 204, connected as shown. . In addition, typically, decoder 200 includes other processing elements (not shown).

Buffer memory 201 (buffer) stores (e.g., in a non-ephemeral manner) at least one block of an AAC MPEG-4 encoded audio bitstream received by decoder 200. When operating decoder 200, a sequence of bitstream blocks is presented from buffer 201 to deformer 205.

In a variation of the embodiment of FIG. 3, an APU that is not a decoder (e.g., APU 500 of FIG. 6) includes a buffer memory (e.g., a buffer memory identical to buffer 201) that stores (e.g., in a non-ephemeral manner) at least one block of encoded audio bitmaps. stream (eg, an AAC MPEG-4 audio bitstream) of the same type received by buffer 201 of FIG. 3 or fig. 4 (that is, an encoded audio bitstream that includes eSBR metadata).

With reference again to FIG. 3, a deformer 205 is coupled and configured to demultiplex each bitstream block to extract SBR metadata (including quantized envelope data) and eSBR metadata (and typically also other metadata) from it, presenting at least the eSBR metadata and SBR metadata to eSBR processing stage 203 and typically also provide other extracted metadata to decoding subsystem 202 (and optionally also to control bit generator 204). A deformer 205 is also attached and configured to extract audio data from each block of the bitstream, and provide the extracted audio data to a decoding subsystem 202 (decoding stage).

The system according to FIG. 3 optionally also includes a post processor 300. The post processor 300 includes a buffer memory 301 (buffer) and other processing elements (not shown), including

- 6 044947 at least one processing element attached to the buffer 301. The buffer 301 stores (for example, in a non-ephemeral manner) at least one block (or frame) of decoded audio data received by the post processor 300 from the decoder 200. The processing elements of the post processor 300 are attached and executed with the ability to receive and adaptively process a sequence of blocks (or frames) of decoded audio signal output from buffer 301 using metadata output from decoding subsystem 202 (and/or deformer 205) and/or control bits output from decoder stage 204 200 .

The audio decoding subsystem 202 of the decoder 200 is configured to decode the audio data extracted by the parser 205 (such decoding may be referred to as a main decoding operation) to generate decoded audio data, and provide the decoded audio data to the eSBR processing stage 203. Decoding is performed in the frequency domain and typically involves inverse quantization followed by spectral processing. Typically, the final processing stage in subsystem 202 applies a frequency domain to time domain transform to the decoded frequency domain audio data such that the output of the subsystem is the decoded time domain audio data. Stage 203 is configured to apply SBR facilities and eSBR facilities indicated by SBR metadata and eSBR metadata (extracted by parser 205) to the decoded audio data (i.e., perform SBR and eSBR processing on the output of decoding subsystem 202 using the SBR and eSBR metadata eSBR) to generate fully decoded audio data that is output (eg, to post processor 300) from decoder 200. Typically, decoder 200 includes memory (accessible from subsystem 202 and stage 203) that stores deformed audio data and metadata output from deformer 205, and stage 203 is configured to access audio data and metadata (including SBR metadata and eSBR metadata) as needed during SBR and eSBR processing. The SBR processing and eSBR processing in stage 203 may be considered post-processing output from main decoding subsystem 202. Optionally, decoder 200 also includes a post-upmix subsystem (which may employ parametric stereo (PS) facilities defined in the MPEG-4 AAC standard using PS metadata extracted by deformer 205 and/or control bits generated in the subsystem 204) that is coupled to and configured to upmix the output of stage 203 to generate a fully decoded upmixed audio signal that is output from decoder 200. Alternatively, post processor 300 is configured to upmix the output of the decoder. 200 (eg, using PS metadata extracted by deformer 205 and/or control bits generated in subsystem 204).

In response to the metadata extracted by the deformer 205, the control bit generator 204 may generate control data, and the control data may be used within the decoder 200 (e.g., in the post upmix subsystem) and/or provided as an output of the decoder 200 (e.g., in post-processor 300 for use in post-processing). In response to metadata extracted from the input bitstream (and, optionally, also in response to control data), stage 204 may generate (and present to post-processor 300) control bits indicating that the decoded audio data output from processing stage 203 eSBRs must undergo a specific type of post-processing. In some embodiments, decoder 200 is configured to provide metadata extracted by deformer 205 from the input bitstream to post-processor 300, and post-processor 300 is configured to perform post-processing on the decoded audio data output from decoder 200 using the metadata.

Fig. 4 is a block diagram of an audio processing unit (APU) 210, which is another embodiment of an inventive audio processing unit. APU 210 is a legacy decoder that is not capable of performing eSBR processing. Any of the components or elements of the APU 210 may be implemented as one or more processes and/or one or more circuits (e.g., ASICs, FPGAs, or other integrated circuits) in hardware, software software or combination of hardware and software. APU 210 includes a buffer memory 201, a bitstream payload deformer 215, an audio decoding subsystem 202 (sometimes referred to as a main decoding stage or main decoding subsystem), and an SBR processing stage 213, connected as shown. In addition, typically, APU 210 includes other processing elements (not shown). APU 210, for example, may be an audio encoder, decoder, or transcoder.

Elements 201 and 202 of APU 210 are identical to equally numbered elements of decoder 200 (of FIG. 3), and the above description will not be repeated. During operation of the APU 210, a sequence of blocks of encoded audio bitstream (AAC MPEG-4 bitstream) received by the APU 210 is presented from the buffer 201 to the deformer 215.

A deformer 215 is attached and configured to demultiplex each block of the bitstream to extract SBR metadata (including quantized envelope data) and typically other metadata therefrom, but ignore eSBR metadata that may be included in the bitstream, in accordance with any embodiment of the present invention. Deformer 215 is configured to add at least SBR metadata to SBR processing stage 213. A deformer 215 is also connected and configured to extract audio data from each block of the bitstream, and present the extracted audio data to a decoding subsystem 202 (decoding stage).

The audio decoding subsystem 202 of the decoder 200 is configured to decode the audio data extracted by the deformer 215 (such decoding may be referred to as a main decoding operation) to generate decoded audio data and provide the decoded audio data to the SBR processing stage 213. Decoding is performed in the frequency domain. Typically, the final processing stage in subsystem 202 applies a frequency domain to time domain transform to the decoded frequency domain audio data such that the output of the subsystem is the decoded time domain audio data. Stage 213 is configured to apply SBR means (but not eSBR means) indicated by SBR metadata (extracted by deformer 215) to the decoded audio data (i.e., perform SBR processing on the output of decoding subsystem 202 using SBR metadata) to generate a complete decoded audio data that is output (eg, to post processor 300) from APU 210. Typically, APU 210 includes memory (accessible from subsystem 202 and stage 213) that stores deformed audio data and metadata output from warp 215, and stage 213 is configured to access audio data and metadata (including SBR metadata) as needed during SBR processing. The SBR processing in stage 213 may be considered a post-processing output from main decoding subsystem 202. Optionally, APU 210 also includes a post-upmix subsystem (which may employ parametric stereo (PS) facilities defined in the MPEG-4 AAC standard using PS metadata extracted by deformer 215) that is coupled to and configured to perform up-mixing. mixing on the output of stage 213 to generate a fully decoded upmixed audio signal that is output from APU 210. Alternatively, the post processor is configured to perform upmixing on the output of APU 210 (eg, using PS metadata extracted by deformer 215 , and/or control bits generated in the APU 210).

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

According to some embodiments, eSBR metadata is included (e.g., a small number of control bits that are eSBR metadata are included) in an encoded audio bitstream (e.g., an MPEG-4 AAC bitstream) such that legacy decoders (which are not implemented with ability to parse eSBR metadata and use whatever eSBR facility to which the eSBR metadata refers) may ignore eSBR metadata but still decode the bitstream as much as possible without using eSBR metadata or any facility The eSBR, to which the eSBR metadata refers, is typically without any significant degradation in the quality of the decoded audio signal. However, eSBR decoders configured to parse the bitstream to identify eSBR metadata and to use at least one eSBR means in response to the eSBR metadata will have the benefits of using at least one such eSBR means. Therefore, embodiments of the invention provide a means for intelligently transmitting enhanced spectrum band replication (eSBR) control data or metadata in a backwards-compatible manner.

Typically, eSBR metadata in a bitstream is indicative of (eg, indicative of at least one characteristic or parameter) one or more of the following eSBR features (which are described in the MPEG USAC standard, and which may or may not have been applied by the encoder during generation of the bitstream flow):

harmonic transposition and additional pre-processing by pasting using KZF (pre-alignment).

For example, the eSBR metadata included in the bitstream may be indicative of parameter values (described in the USAC MPEG standard and the present invention):

sbrPatchingMode[ch], sbrOversamplingFlag[ch], sbrPitchInBins[ch], sbrPitchInBins[ch] and bs_sbr_preprocessing.

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As used herein, the designation X[ch], where X is a parameter, indicates that the parameter refers to the channel (ch) of the audio content of the encoded bit stream to be decoded. For the sake of simplicity, we sometimes omit the [ch] expression and assume that the corresponding parameter refers to the audio content channel.

As used herein, the notation X[ch][env], where X is a parameter, denotes that the parameter refers to the SBR envelope (env) of the audio content channel (ch) of the encoded bitstream to be decoded. For the sake of simplicity, we sometimes omit the expressions [env] and [ch], and assume that the corresponding parameter refers to the SBR envelope of the audio content channel.

During decoding of an encoded bitstream, the implementation of harmonic transposition during the eSBR decoding processing stage (for each channel, ch, of audio content specified by the bitstream) is controlled by the following eSBR metadata parameters: sbrPatchingMode[ch]: sbrOversamplingFlag[ch]; sbrPitchInBinsFlag[ch] and sbrPitchInBins[ch].

The value of sbrPatchingMode[ch] specifies the type of transposer used in eSBR: sbrPatchingMode[ch]=1 specifies non-harmonic patching, as described in section 4.6.18.6.3 of the AAC MPEG-4 standard; sbrPatchingMode[ch]=0 specifies SBR harmonic patching as specified in section 7.5.3 or 7.5.4 of the USAC MPEG USAC standard.

The value sbrOversamplingFlag[ch] specifies the use of signal-adaptive frequency domain oversampling in eSBR in combination with DFT-based SBR harmonic stitching, as described in section 7.5.3 of the USAC MPEG standard. This flag controls the size of the DFTs that are used in the transposer: 1 indicates signal-adaptive frequency domain resampling is enabled, as described in section 7.5.3.1 of the USAC MPEG standard; 0 indicates signal-adaptive frequency domain resampling disabled, as described in section 7.5.3.1 of the USAC MPEG standard.

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

The sbrPitchInBins[ch] value controls the addition of cross product terms to the SBR harmonic transposer. The value of sbrPitchinBins[ch] is an integer value in the range [0.127] and represents the distance measured in frequency bins for a 1536-point DFT operating at the base encoder sampling rate.

In the case where the MPEG-4 AAC bitstream indicates a pair of SBR channels whose channels are not paired (instead of a single SBR channel), the bitstream is indicating two instances of the above syntax (for harmonic or non-harmonic transposition), one for each channel sbr_channel_pair_element().

The eSBR facility's harmonic transposition typically improves the quality of decoded music signals with relatively low crossover frequencies. Nonharmonic transposition (ie, inherited spectral pasting) typically improves speech signals. Hence, the starting point when deciding which type of transposition is preferable for encoding a particular audio content is to select the transposition method depending on the speech/music detection, with harmonic transposition being performed on the musical content, and spectral pasting on speech content.

The execution of pre-alignment during eSBR processing is controlled by the value of a one-bit eSBR metadata parameter known as bs sbr preprocessing, in the sense that pre-alignment is performed or not performed depending on the value of this single bit. When the SBR FQF stitching algorithm is used, as described in section 4.6.18.6.3 of the MPEG-4 AAC standard, a pre-alignment step may be performed (when specified by the bs_sbr_preprocessing parameter) in an attempt to avoid lack of continuity in the spectral envelope profile of the high-frequency signal fed to the subsequent equalizer envelope (the envelope corrector acts as another stage of eSBR processing). Pre-equalization typically improves the effect of the subsequent envelope correction stage, resulting in a high-band signal that is perceived to be more stable.

The overall bit rate requirement for inclusion in eSBR metadata of an MPEG-4 AAC bitstream specifying the eSBR (harmonic transposition and pre-equalization) facilities mentioned above is expected to be on the order of several hundred bits per second, since only the distinctive control data required to perform eSBR processing are transmitted in accordance with some embodiments of the invention. Legacy decoders may ignore this information since it is included in a backwards compatible manner (as explained later). Therefore, the detrimental impact on bit rates associated with inclusion of eSBR metadata is negligible for a number of reasons, including the following:

the bit rate degradation (caused by inclusion in the eSBR metadata) is a very small fraction of the total bit rate, since only the distinctive control data needed to perform eSBR processing is transmitted (rather than transmitting the SBR control data simultaneously); And

- 9 044947 The setting of SBR-related control information is typically independent of the transposition details.

Thus, embodiments of the invention provide a means for intelligently transmitting enhanced spectrum band replication (eSBR) control data or metadata in a backwards-compatible manner. Efficient transmission of eSBR control data reduces memory requirements in decoders, encoders and transcoders employing aspects of the invention, while not being perceptibly adversely affected by bit rates. Moreover, the complexity and processing requirements associated with performing eSBR in accordance with embodiments of the invention are also reduced since the SBR data only needs to be processed once and there is no concurrent transmission that would occur if the eSBR were processed as a complete separate object type in AAC MPEG-4 instead of being built into the AAC MPEG-4 codec in a backwards-compatible manner.

Then, with reference to FIG. 7, we will describe the elements of a block (raw_data_block) of an MPEG-4 AAC bitstream in which eSBR metadata is included in accordance with some embodiments of the present invention. Fig. 7 is a block diagram (raw_data_block) of an MPEG-4 AAC bitstream, showing some of its segments.

An MPEG-4 AAC bitstream block may include at least one single channel element() (e.g., the single channel element shown in FIG. 7), and/or at least one channel pair element() (not particularly shown in Fig. 7, although it may be present), including audio data for the audio program. The block may also include a number of fill_elements (eg, fill element 1 and/or fill element 2 of FIG. 7) including data (eg, metadata) related to the program. Each single_channel_element() includes an identifier (eg, ID1 of FIG. 7) indicating the start of the single channel element, and may include audio data indicating another channel of the multi-channel audio program. Each channel_pair_element includes an identifier (not shown in FIG. 7) indicating the start of the channel pair element, and may include audio data indicating two program channels.

The fill element (herein referred to as a fill element) of the MPEG-4 AAC bitstream includes an identifier (ID2 of FIG. 7) indicating the start of the fill element, and fill data after the identifier. ID2 may consist of a three-bit unsigned integer, most significant bit first (uimsbf), having the value 0x6. The padding data may include an extension_payload() element (sometimes referred to herein as an extension payload), whose syntax is shown in Table 1. 4.57 AAC MPEG-4 standard. Several extension payload types exist and are identified by the extension_type parameter, which is a four-bit unsigned integer, most significant bit first (uimsbf).

The padding data (e.g., its extension payload) may include a header or identifier (e.g., header 1 of FIG. 7) that indicates a segment of padding data that is indicative of an SBR object (i.e., the header initializes the type of the SBR object referenced as sbr_extension_data() in the AAC MPEG-4 standard). For example, a spectrum band replication (SBR) extension payload is identified by the value '1101' or '1110' as regards the extension_type field in the header, with '1101' identifying the extension payload with SBR data and '1110' identifying both the extension payload with SBR data with cyclic redundancy code (CRC) to verify the correctness of the SBR data.

When a header (eg, an extension_type field) initializes an SBR object type, SBR metadata (sometimes referred to as spectrum band replication data and referenced as sbr_data() in the MPEG-4 AAC standard) follows the header, and at least one band replication extension element spectrum (eg, the SBR extension element of the padding element 1 of FIG. 7) may follow the SBR metadata. Such a spectrum band replication extension element (bitstream segment) is referenced as the sbr_extension() container in the MPEG-4 AAC standard. The spectrum band replication extension element optionally includes a header (eg, the SBR extension header of padding element 1 of FIG. 7).

The MPEG-4 AAC standard specifies that the spectrum band replication extension element may include PS (parametric stereophony) data for program audio data. The MPEG-4 AAC standard assumes that when the header of a padding element (eg, its extension payload) initializes an SBR object type (as header1 does in FIG. 7) and the padding element's spectrum band replication extension element includes PS data, a filler element (eg, its extension payload) includes spectrum band replication data, and a bs_extension_id parameter whose value (ie, bs_extension_id=2) indicates that the PS data is included in the spectrum band replication extension element of the filler element.

In accordance with some embodiments of the present invention, eSBR metadata (eg, a flag indicating whether enhanced spectrum band replication (eSBR) processing should be performed on the audio content of the block). For example, such a flag is indicated in the filling element 1 in FIG. 7, where the flag occurs after the header (SBR extension header of the padding element 1) of the SBR extension element of the padding element 1. Optionally, such a flag and additional eSBR data are included in the spectrum band replication extension element after the spectrum band replication extension element header (eg, in the SBR extension element of padding element 1 in FIG. 7, after the SBR extension header). In accordance with some embodiments of the present invention, a padding element that includes eSBR metadata also includes a bs_extension_id parameter whose value (eg, bs_extension_id=3) indicates that eSBR metadata is included in the padding element and that eSBR processing should be performed on the audio content of the relevant block.

In accordance with some embodiments of the invention, metadata, eSBR, is included in a padding element (eg, padding element 2 of FIG. 7) of the MPEG-4 AAC bitstream, other than in the spectrum band replication extension element (SBR extension element) of the padding element. The reason is that pad elements containing extension_payload() with SBR data or SBR data with CRC do not contain any other extension payload of any other extension type. Therefore, in embodiments where eSBR metadata is stored in its own extension payload, a separate padding element is used to store eSBR metadata. Such pad element includes an identifier (eg, ID2 of FIG. 7) indicating the beginning of the pad element, and pad data after the identifier. The padding data may include an extension_payload() element (sometimes referred to herein as an extension payload), whose syntax is shown in Table 1. 4.57 AAC MPEG-4 standard. The padding data (eg, its extension payload) includes a header (eg, header2 of padding element 2 of FIG. 7) that is indicative of an eSBR object (i.e., the header initializes an enhanced spectrum band replication (eSBR) object type), and the padding data (eg, its extension payload) includes eSBR metadata after the header. For example, the filling element 2 of FIG. 7 includes such a header (header2) and also includes, after the header, eSBR metadata (i.e., a flag in padding element 2 that indicates whether enhanced spectrum band replication (eSBR) processing should be performed on the audio content of the block ). Optionally, additional eSBR metadata is also included in the padding data of padding element 2 of FIG. 7 after header 2. In the embodiments described in this paragraph, the header (eg, header 2 of FIG. 7) has an identification value that is not one of the traditional values specified in table. 4.57 of the MPEG-4 AAC standard, and is instead indicative of the eSBR extension payload (so that the extension_type field indicates that the padding data includes eSBR metadata).

In a first group of embodiments, the invention is an audio signal processing unit (eg, a decoder) comprising a memory (eg, buffer 201 of FIG. 3 or 4) configured to store at least one block of encoded audio bitstream (eg, by at least one AAC MPEG-4 bitstream block);

a bitstream payload deformer (eg, element 205 of FIG. 3 or element 215 of FIG. 4) coupled to the memory and configured to demultiplex at least one portion of said bitstream block; and a decoding subsystem (e.g., elements 202 and 203 of FIG. 3 or elements 202 and 213 of FIG. 4) coupled to and configured to decode at least one portion of the audio content of said bitstream block, the block including an element padding, including an identifier indicating the beginning of a padding element (for example, the id_syn_ele identifier having the value 0x6, according to Table 4.85 of the MPEG-4 AAC standard), and padding data after the identifier, wherein the padding data includes at least one flag an attribute identifying whether enhanced spectrum band replication (eSBR) processing should be performed on the audio content of the block (eg, using the spectrum band replication data and eSBR metadata included in the block).

A flag is eSBR metadata, and an example of a flag is the sbrPatchingMode flag. Another example of a flag is the harmonic SBR flag. Both of these flags indicate whether a basic form of spectrum replication or an advanced form of spectrum replication should be performed on the block's audio data. The basic form of spectrum replication is spectral pasting, and an advanced form of spectrum band replication is harmonic transposition.

In some embodiments, the padding data also includes additional eSBR metadata (ie, eSBR metadata other than a flag).

The memory may be a buffer memory (eg, an implementation of buffer 201 of FIG. 4) that stores (eg, in a non-ephemeral manner) at least one block of an encoded audio bitstream.

- 11 044947

It is estimated that the complexity of performing eSBR processing (using harmonic transposition and eSBR pre-alignment) by an eSBR decoder while decoding an MPEG-4 AAC bitstream that includes eSBR metadata (indicating these eSBR facilities) would be as follows (for a typical decoding with the specified parameters):

harmonic transposition (16 kbps, 14400/28800 Hz);

based on DFT: 3.68 WMOPS (weighted million operations per second);

based on KZF: 0.98 WMOPS;

pre-processing of the insert using KZF (pre-alignment): 0.1 WMOPS. It is known that DFT-based transposition typically performs better than QFT-based transposition when applied to transients.

In accordance with some embodiments of the present invention, a padding element (of an encoded audio bitstream) that includes eSBR metadata also includes a parameter (eg, a bs_extension_id parameter) whose value (eg, bs_extension_id=3) signals that the metadata eSBRs are included in the pad element, and that eSBR processing must be performed on the audio content of the relevant block, and/or parameter (e.g., the same bs_extension_id parameter whose value (e.g., bs_extension_id=2) signals that the pad element's sbr_extension() container includes PS data. For example, as indicated in Table 1 below, such a parameter having a value of bs_extension_id=2 may signal that the pad element's sbr_extension() container includes PS data, and such a parameter having a value of bs_extension_id =3 may signal that the padding element's sbr_extension() container includes eSBR metadata.

Table 1

bs_extension_id Meaning 0 Reserved 1 Reserved 2 EXTENSION_ID_PS 3 EXTENSION_ID_ESBR

In accordance with some embodiments of the invention, the syntax of each spectrum band replication extension element that includes eSBR metadata and/or PS data is as set forth in Table. 2 above (in which sbr_extension() denotes a container that is a spectrum band replication extension element, bs_extension_id is as described in Table 1 above, ps_data denotes PS data, and esbr_data denotes eSBR metadata).

table 2

sbr_extension(bs_extension_id, num_bits_left) { switch (bs_extension_id) { case EXTENSION_ID_PS: num_bits_left -= ps_data(); Note 1 break; case EXTENSION_ID_ESBR: num bits left -= esbr data(); Note 2 break; default: bs_f i1l_bi ts; num_bits_left=0; break;

- 12044947

} } Note 1: ps_data() returns the number of bits read. Note 2: esbr_data() returns the number of bits read.

In an exemplary embodiment, esbr_data() referred to in Table. 2 above is indicating the values of the following metadata parameters:

1. one-bit metadata parameter, bs_sbr_preprocessing; And

2. for each channel (ch) of the audio content of the encoded bitstream to be decoded, each of the parameters described above: sbrPatchingMode[ch];

sbrOversamplingFlag[ch]; sbrPitchInBinsFlag[ch]; and sbrPitchInBins[ch].

For example, in some embodiments, esbr_data() may have the syntax specified in Table. 3 to specify these metadata parameters.

Table 3

Syntax Number of bits esbr_data(id_aac, bs_coupling) { bs_sbr_preprocessing; 1 if (id_aac == ID_SCE) { if (sbrPatchingMode[0] == 0) { 1 sbrOversamplingFlag[0]; 1 if (sbrPitchlnBinsFlag[0]) 1 sbrPitchlnBins[0]; 7 else sbrPitchlnBins[0]=0; } else { sbrOversamplingFlag[0]=0; sbrPitchlnBins[0]=0; }

- 13 044947

} else if (id_aac == ID_CPE) { If (bs_coupling) { if (sbrPatchingMode[0,1] == 0) { 1 sbrOversamplingFlag[0,1]; 1 if (sbrPitchlnBinsFlag[0,1]) 1 sbrPitchlnBins[0,1]; 7 else sbrPitchlnBins[0,1 ] = 0; } else { sbrOversamplingFlag[0, 1 ] = 0; sbrPitchlnBins[0,1 ] = 0; } } else { /* bs_coupling == 0 */ if (sbrPatchingMode[0] == 0) { 1 sbrOversamplingFlag[0]; 1 if (sbrPitchlnBinsFlag[0]) 1 sbrPitchlnBins[0]; 7 else sbrPitchlnBins[ 0 ] = 0; } else { sbrOversamplingFlag[0]=0; sbrPitchlnBins[ 0 ] = 0; } if (sbrPatchingMode[1] == 0) { 1 sbrOversamplingFlag[1]; 1 if (sbrPitchlnBinsFlag[1]) 1 sbrPitchlnBins[1]; 7 else sbrPitchlnBins[ 1]=0; } else { sbrOversamplingFlag[ 1 ] = 0; sbrPitchlnBins[ 1 ] = 0; } } } } Note: bs sbr preprocessing is defined as described in section 6.2.12 of ISO/IEC 23003-3:2012. sbrPatchingMode[ch], sbrOversamplingFlag[ch] , sbrPitchlnBinsFlag[ch] and sbrPitchlnBins[ch] are defined as described in section 7.5 of ISO/IEC 23003-3:2012.

The above syntax allows for a rational implementation of an advanced form of spectrum band replication, such as harmonic transposition, as an extension of the legacy decoder. More precisely, the eSBR data from Table. 3 include only those parameters necessary to perform an advanced form of spectrum band replication that are not already supported in the bitstream and are not directly inferred from parameters already supported in the bitstream. All other parameters and processing data needed to perform an advanced form of spectrum band replication are derived from pre-existing parameters at already defined locations in the bitstream.

For example, a HE-AAC MPEG-4 or HE-AAC v2 compatible decoder may be extended to include an advanced form of spectrum band replication, such as harmonic transposition. This advanced form of spectrum band replication is in addition to the basic form of spectrum band replication already supported by the decoder. In the context of a HEAAC or HE-AAC v2 MPEG-4 decoder, this basic form of spectrum band replication is a means of SBR spectral pasting using FQF, as defined in section 4.6.18 of the AAC MPEG4 standard.

When performing an advanced form of spectrum band replication, the extended HE-AAC decoder can reuse many of the bitstream parameters already included in the SBR bitstream extension payload. Specific parameters that can be reused, for example, include the various parameters that define the frequency band summary table. These parameters include bs_start_freq (a parameter that specifies the start of the frequency summary table parameter), bs_stop_freq (a parameter that specifies the end of the frequency summary table), bs_freq_scale (a parameter that specifies the number of frequency bands per octave), and bs_alter_scale (a parameter that changes the scale frequency bands). Parameters that can be reused also include parameters that define the noise band table (bs_noise_bands) and the limit band table parameters (bs_limiter_bands). Accordingly, in various embodiments, at least some of the equivalent parameters defined in the USAC standard are not included in the bitstream, thereby reducing overhead and control data in the bitstream. Typically, in cases where an AAC-specified parameter has an equivalent USAC-specified parameter, the equivalent USAC-specified parameter has the same name as the AAC-specified parameter, for example, envelope scale factor, E _Or i _gMapped . However, the equivalent parameter specified in the USAC standard typically has a different value that is tailored to the processing of the enhanced SBR defined in the USAC standard rather than to the processing of the SBR defined in the AAC standard.

In addition to numerous parameters, other data elements may also be reused by the extended HE-AAC decoder when performing an advanced form of spectrum band replication in accordance with embodiments of the invention. For example, envelope data and noise floor data can also be extracted from bs_data_env (envelope scale factors) and bs_noise_env (noise floor scale factors) data and used during an advanced form of spectrum band replication.

Essentially, these embodiments use configuration parameters and envelope data already supported by a legacy HE-AAC or HE-AAC v2 decoder in the SBR extension payload to enable an advanced form of spectrum band replication while requiring as little additional transmitted data as possible. The metadata was originally tailored for a basic form of HFR (eg, spectral pasting SBR), but, in accordance with embodiments, is used for an advanced form of HFR (eg, harmonic transposition eSBR). As discussed earlier, metadata typically represents performance parameters (e.g., envelope scaling factors, noise floor scaling factors, time/frequency grid parameters, sinusoidal complement information, variable frequency/bandwidth, inverse filtering mode, envelope resolution, smoothing mode, frequency interpolation mode). adapted and intended for use with a basic form of HFR (e.g. linear transform). However, this metadata, combined with additional metadata parameters specific to the advanced form of HFR (eg, harmonic transposition), can be used to efficiently and effectively process audio data using the advanced form of HFR.

Accordingly, extended decoders that support an advanced form of spectrum band replication can be created in a very efficient manner by relying on already defined bitstream elements (such as those in the SBR extension payload) and adding only those parameters that are necessary to support the advanced form of replication spectrum bands (in the fill element extension payload). This data reduction feature, combined with placing newly added parameters in reserved data fields such as an extension container, significantly reduces the barriers to creating a decoder that supports advanced spectrum band replication, ensuring that the bitstream is backwards compatible with a legacy decoder that does not support the advanced form. replication of spectrum bands.

- 15 044947

In table 3, the number in the right column indicates the number of bits of the corresponding parameter in the left column.

In some embodiments, the SBR object type defined in MPEG-4 AAC is updated to contain an SBR facility or aspects of an enhanced SBR facility (eSBR), as signaled in the SBR extension element (bs_extension_id==EXTENSION_ID_ESBR).

In some embodiments, the invention is a method including the step of encoding audio data to generate an encoded bitstream (e.g., an MPEG-4 AAC bitstream), including by including eSBR metadata in at least one segment of at least one block of encoded bit stream and audio data into at least one other block segment. In typical embodiments, the method includes the step of multiplexing audio data with eSBR metadata in each block of the encoded bitstream. In a typical decoding of an encoded bitstream in an eSBR decoder, the decoder extracts eSBR metadata from the bitstream (including by parsing and demultiplexing eSBR metadata and audio data) and uses the eSBR metadata to process the audio data to generate a decoded audio data stream.

Another aspect of the invention is an eSBR decoder configured to perform eSBR processing (e.g., using at least one of the eSBR features known as harmonic transposition or pre-equalization) while decoding an encoded audio stream (e.g., an AAC MPEG-4 bitstream ), which does not include eSBR metadata. An example of such a decoder will be described with reference to FIG. 5.

The eSBR decoder (400) of FIG. 5 includes a buffer memory 201 (which is identical to the memory 201 of FIGS. 3 and 4), a bitstream payload deformer 215 (which is identical to the deformer 215 of FIG. 4), an audio decoding subsystem 202 (sometimes referred to as the main decoding stage or main decoding subsystem, and which is identical to the main decoding subsystem 202 of FIG. 3), an eSBR control data generation subsystem 401, and an eSBR processing stage 203 (which is identical to the stage 203 of FIG. 3, connected as shown. Additionally, typically, a decoder 400 includes other processing elements (not shown).

When operating decoder 400, a sequence of blocks of encoded audio bitstream (AAC MPEG-4 bitstream) received by decoder 400 is presented from buffer 201 to deformer 215.

A deformer 215 is attached and configured to demultiplex each bitstream block to extract SBR metadata (including quantized envelope data) and typically other metadata therefrom. The deformer 215 is configured to add at least SBR metadata to the eSBR processing stage 203. A deformer 215 is also attached and configured to extract audio data from each block of the bit stream, and provide the extracted audio data to a decoding subsystem 202 (decoding stage).

The audio decoding subsystem 202 of the decoder 400 is configured to decode the audio data extracted by the deformer 215 (such decoding may be referred to as a main decoding operation) to generate decoded audio data and provide the decoded audio data to the eSBR processing stage 203. Decoding is performed in the frequency domain. Typically, the final processing stage in subsystem 202 applies a frequency domain to time domain transform to the decoded frequency domain audio data such that the output of the subsystem is the decoded time domain audio data. Stage 203 is configured to apply SBR facilities (and eSBR facilities) indicated by SBR metadata (extracted by deformer 215) and eSBR metadata generated in subsystem 401 to the decoded audio data (i.e., perform SBR and eSBR processing on the output of subsystem 202 decoding using SBR and eSBR metadata) to generate fully decoded audio data that is output from decoder 400. Typically, decoder 400 includes memory (accessible from subsystem 202 and stage 203) that stores deformed audio data and metadata output from the deformer 215 (and optionally also subsystems 401), and stage 203 is configured to access audio data and metadata as needed during SBR and eSBR processing. The SBR processing in stage 203 may be considered a post-processing output from main decoding subsystem 202. Optionally, decoder 400 also includes a post-upmix subsystem (which may employ parametric stereo (PS) facilities defined in the MPEG-4 AAC standard using PS metadata extracted by deformer 215) that is coupled to and configured to perform up-mixing. mixing on the output of stage 203 to generate a fully decoded upmixed audio signal that is output from APU 210.

The control data generation subsystem 401 of FIG. 5 is coupled and configured to detect at least one property of the encoded audio bitstream to be decoded and generate eSBR control data (which may be or include

- 16 044947 eSBR metadata of any of the types included in the encoded audio bitstreams, in accordance with other embodiments of the invention) in response to at least one result of the detection step. eSBR control data is added to cascade 203 to drive the application of individual eSBRs or a combination of eSBRs when a particular property (or combination of properties) of the bitstream is detected and/or control the application of such eSBRs. For example, in order to control the execution of eSBR processing using harmonic transposition, some embodiments of the control data generation subsystem 401 would include: a music detector (e.g., a simplified version of a traditional music detector) to set the sbrPatchingMode[ch] parameter (and present the set parameter to cascade 203) in response to determining that the bitstream is or is not indicative of music; a transient detector for setting the parameter sbrOversamplingFlag[ch] (and presenting the set parameter to stage 203) in response to detecting the presence or absence of transients in the audio content indicated by the bit stream; and/or a pitch detector for setting the parameters sbrPitchInBinsFlag[ch] and sbrPitchInBins[ch] (and presenting the set parameters to stage 203) in response to detecting the pitch of the audio content indicated by the bit stream. Other aspects of the invention include methods for decoding an audio bitstream performed by any embodiment of the inventive decoder described in this paragraph and the preceding paragraph.

Aspects of the invention include a type of encoding or decoding method that any embodiment of an inventive APU, system, or device is configured (or programmed) to perform. Other aspects of the invention include a system or device configured (e.g., programmed) to perform any embodiment of an inventive method, and a machine-readable medium (e.g., a disk) that stores a computer program (e.g., in a non-ephemeral manner) for implementing any an embodiment of a method or its stages having features of the invention. For example, an inventive system may be or include a general purpose programmable processor, digital signal processor, or microprocessor programmed with software or firmware and/or otherwise configured to perform any of a variety of operations on data, including, implementation of a method or its stages that has features of an invention. Such a general purpose processor may be or include a computer system including an input device, memory, processing circuitry programmed (and/or otherwise configured) to execute an embodiment of an inventive method (or steps thereof) in response to information presented to him.

Embodiments of the present invention may be implemented in hardware, firmware, or software, or a combination of both (eg, as a programmable gate array). Unless otherwise indicated, the algorithms and processes included as part of the invention are not, by their nature, related to any particular computer or other device. In particular, various general purpose machines may be used with programs written in accordance with the teachings herein, or it may be more convenient to construct a more specialized device (eg, integrated circuits) to perform the required method steps. Thus, the invention may be implemented in one or more computer programs executing on one or more programmable computer systems (for example, implementations of any of the elements of FIG. 1 or encoder 100 of FIG. 2 (or element thereof), or decoder 200 of Fig. 3 (or element thereof), or decoder 210 of Fig. 4 (or element thereof) or decoder 400 of Fig. 5 (or element thereof)), each of which contains at least one processor, at least one system data storage (including volatile or nonvolatile memory elements and/or storage elements), at least one input device or port, and at least one output device or port. The control program is applied to the input data to perform the functions described in the materials of this application, and generates output information. The output information is sent to one or more output devices in a known manner.

Each such program may be implemented in any desired computer language (including machine, layout, or high-level procedural, logical, or object-oriented programming languages) for exchanging information with the computer system. In either case, the language may be a compiled or interpreted language.

For example, when implemented by sequences of computer software instructions, various functions and steps of embodiments of the invention may be implemented by sequences of multi-threaded software instructions running on suitable digital signal processing hardware, in which case, various devices, steps and functions of embodiments may correspond to portions of instructions software.

- 17 044947

Each such computer program is preferably stored on or loaded onto a storage media or device (e.g., solid-state memory or media, or magnetic or optical media) readable by a general purpose or special purpose programmable computer for configuring and controlling the computer when the storage media or device read by a computer system to perform the procedures described herein. The inventive system may also be implemented as a machine-readable storage medium configured by a computer program (i.e., storing a computer program), wherein the storage medium so configured causes the computer system to act in a specific and predetermined manner to perform the functions described in the materials of this application.

A number of embodiments of the invention have been described. However, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Many modifications and variations of the present invention are possible in light of the above teachings. For example, in order to facilitate efficient implementations, phase shifts can be used in combination with signal decomposition and signal synthesis filter banks of the complex FQF. The signal decomposition filter bank is responsible for filtering the time domain lowband signal generated by the main decoder into a plurality of subbands (eg, FQF subbands). The signal decomposition filter bank is responsible for combining the reconstructed high-pass band created by the selected HFR technology (as indicated by the accepted sbrPatchingMode parameter) with the decoded low-pass band to synthesize a wideband audio output signal. A given filter bank implementation operating in a particular sampling rate mode, such as normal double-rate operation or SBR downsampling mode, however, must not have phase shifts that are dependent on the bitstream. The QFT combs used in SBR are an extension of the complex exponential function of cosine-modulated filter comb theory. It can be shown that the limitations of spurious signal rejection become obsolete when the cosine modulation filter bank is expanded to complex exponential modulation. Thus, with regard to SBR QF combs, both the signal decomposition filters, h _k (n), and the signal synthesis filters, f _k (n), can be defined by (i/ 1W h _k (n) = = p ₀ (n) exp i^ik + y η - y ζ/ξ 0<n<N;0<k< Μ ₍₁₎ where p ₀ (n) is a real-valued symmetrical or asymmetrical prototype filter (typically a prototype low-pass filter) , M denotes the number of channels, and N is the order of the prototype filter. The number of channels used in a signal decomposition filter bank may be different from the number of channels used in a signal synthesis filter bank. For example, a signal decomposition filter bank may have 32 channels, and the signal synthesis filter bank can have 64 channels. When operating the signal synthesis filter bank in downsampling mode, the signal synthesis filter bank can only have 32 channels. Since the subband samples from the filter bank are complex valued, an additive possibly channel-dependent phase shift stage can be added to signal decomposition filter bank. These additional phase shifts must be compensated for before the signal synthesis filter bank. Although the phase shift elements can in principle be arbitrary values without disrupting the signal decomposition/synthesis chain using FQF, they can also be limited to certain values to control compliance. The SBR signal will be influenced by the choice of phase multipliers, while the low pass signal coming from the main decoder will not. The sound quality of the output signal is not affected.

The prototype filter coefficients, p ₀ (n), can be limited by the length, L, of 640, as shown in Table. 4 below.

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Table 4

η rho (η) η ρο (η) η ρο (η) 0 0.0000000000 214 0.0019765601 428 0.0117623832 1 -0.0005525286 215 -0.0032086896 429 0.0163701258 2 -0.0005617692 216 -0.0085711749 430 0.0207997072 3 -0.0004947518 217 -0.0141288827 431 0.0250307561 4 -0.0004875227 218 -0.0198834129 432 0.0290824006 5 -0.0004893791 219 -0.0258227288 433 0.0329583930 6 -0.0005040714 220 -0.0319531274 434 0.0366418116 7 -0.0005226564 221 -0.0382776572 435 0.0401458278 8 -0.0005466565 222 -0.0447806821 436 0.0434768782 9 -0.0005677802 223 -0.0514804176 437 0.0466303305 10 -0.0005870930 224 -0.0583705326 438 0.0495978676 eleven -0.0006132747 225 -0.0654409853 439 0.0524093821 12 -0.0006312493 226 -0.0726943300 440 0.0550460034 13 -0.0006540333 227 -0.0801372934 441 0.0575152691 14 -0.0006777690 228 -0.0877547536 442 0.0598166570 15 -0.0006941614 229 -0.0955533352 443 0.0619602779 16 -0.0007157736 230 -0.1035329531 444 0.0639444805 17 -0.0007255043 231 -0.1116826931 445 0.0657690668 18 -0.0007440941 232 -0.1200077984 446 0.0674525021 19 -0.0007490598 233 -0.1285002850 447 0.0689664013 20 -0.0007681371 234 -0.1371551761 448 0.0703533073 21 -0.0007724848 235 -0.1459766491 449 0.0715826364 22 -0.0007834332 236 -0.1549607071 450 0.0726774642

- 19 044947

23 -0.0007779869 237 -0.1640958855 451 0.0736406005 24 -0.0007803664 238 -0.1733808172 452 0.0744664394 25 -0.0007801449 239 -0.1828172548 453 0.0751576255 26 -0.0007757977 240 -0.1923966745 454 0.0757305756 27 -0.0007630793 241 -0.2021250176 455 0.0761748321 28 -0.0007530001 242 -0.2119735853 456 0.0765050718 29 -0.0007319357 243 -0.2219652696 457 0.0767204924 thirty -0.0007215391 244 -0.2320690870 458 0.0768230011 31 -0.0006917937 245 -0.2423016884 459 0.0768173975 32 -0.0006650415 246 -0.2526480309 460 0.0767093490 33 -0.0006341594 247 -0.2631053299 461 0.0764992170 34 -0.0005946118 248 -0.2736634040 462 0.0761992479 35 -0.0005564576 249 -0.2843214189 463 0.0758008358 36 -0.0005145572 250 -0.2950716717 464 0.0753137336 37 -0.0004606325 251 -0.3059098575 465 0.0747452558 38 -0.0004095121 252 -0.3168278913 466 0.0741003642 39 -0.0003501175 253 -0.3278113727 467 0.0733620255 40 -0.0002896981 254 -0.3388722693 468 0.0725682583 41 -0.0002098337 255 -0.3499914122 469 0.0717002673 42 -0.0001446380 256 0.3611589903 470 0.0707628710 43 -0.0000617334 257 0.3723795546 471 0.0697630244 44 0.0000134949 258 0.3836350013 472 0.0687043828 45 0.0001094383 259 0.3949211761 473 0.0676075985 46 0.0002043017 260 0.4062317676 474 0.0664367512 47 0.0002949531 261 0.4175696896 475 0.0652247106 48 0.0004026540 262 0.4289119920 476 0.0639715898 49 0.0005107388 263 0.4402553754 477 0.0626857808 50 0.0006239376 264 0.4515996535 478 0.0613455171 51 0.0007458025 265 0.4629308085 479 0.0599837480 52 0.0008608443 266 0.4742453214 480 0.0585915683 53 0.0009885988 267 0.4855253091 481 0.0571616450 54 0.0011250155 268 0.4967708254 482 0.0557173648 55 0.0012577884 269 0.5079817500 483 0.0542452768 56 0.0013902494 270 0.5191234970 484 0.0527630746

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57 0.0015443219 271 0.5302240895 485 0.0512556155 58 0.0016868083 272 0.5412553448 486 0.0497385755 59 0.0018348265 273 0.5522051258 487 0.0482165720 60 0.0019841140 274 0.5630789140 488 0.0466843027 61 0.0021461583 275 0.5738524131 489 0.0451488405 62 0.0023017254 276 0.5845403235 490 0.0436097542 63 0.0024625616 277 0.5951123086 491 0.0420649094 64 0.0026201758 278 0.6055783538 492 0.0405349170 65 0.0027870464 279 0.6159109932 493 0.0390053679 66 0.0029469447 280 0.6261242695 494 0.0374812850 67 0.0031125420 281 0.6361980107 495 0.0359697560 68 0.0032739613 282 0.6461269695 496 0.0344620948 69 0.0034418874 283 0.6559016302 497 0.0329754081 70 0.0036008268 284 0.6655139880 498 0.0315017608 71 0.0037603922 285 0.6749663190 499 0.0300502657 72 0.0039207432 286 0.6842353293 500 0.0286072173 73 0.0040819753 287 0.6933282376 501 0.0271859429 74 0.0042264269 288 0.7022388719 502 0.0257875847 75 0.0043730719 289 0.7109410426 503 0.0244160992 76 0.0045209852 290 0.7194462634 504 0.0230680169 77 0.0046606460 291 0.7277448900 505 0.0217467550 78 0.0047932560 292 0.7358211758 506 0.0204531793 79 0.0049137603 293 0.7436827863 507 0.0191872431 80 0.0050393022 294 0.7513137456 508 0.0179433381 81 0.0051407353 295 0.7587080760 509 0.0167324712 82 0.0052461166 296 0.7658674865 510 0.0155405553 83 0.0053471681 297 0.7727780881 511 0.0143904666 84 0.0054196775 298 0.7794287519 512 -0.0132718220 85 0.0054876040 299 0.7858353120 513 -0.0121849995 86 0.0055475714 300 0.7919735841 514 -0.0111315548 87 0.0055938023 301 0.7978466413 515 -0.0101150215 88 0.0056220643 302 0.8034485751 516 -0.0091325329 89 0.0056455196 303 0.8087695004 517 -0.0081798233 90 0.0056389199 304 0.8138191270 518 -0.0072615816

- 21 044947

91 0.0056266114 305 0.8185776004 519 -0.0063792293 92 0.0055917128 306 0.8230419890 520 -0.0055337211 93 0.0055404363 307 0.8272275347 521 -0.0047222596 94 0.0054753783 308 0.8311038457 522 -0.0039401124 95 0.0053838975 309 0.8346937361 523 -0.0031933778 96 0.0052715758 310 0.8379717337 524 -0.0024826723 97 0.0051382275 311 0.8409541392 525 -0.0018039472 98 0.0049839687 312 0.8436238281 526 -0.0011568135 99 0.0048109469 313 0.8459818469 527 -0.0005464280 100 0.0046039530 314 0.8480315777 528 0.0000276045 101 0.0043801861 315 0.8497805198 529 0.0005832264 102 0.0041251642 316 0.8511971524 530 0.0010902329 103 0.0038456408 317 0.8523047035 531 0.0015784682 104 0.0035401246 318 0.8531020949 532 0.0020274176 105 0.0032091885 319 0.8535720573 533 0.0024508540 106 0.0028446757 320 0.8537385600 534 0.0028446757 107 0.0024508540 321 0.8535720573 535 0.0032091885 108 0.0020274176 322 0.8531020949 536 0.0035401246 109 0.0015784682 323 0.8523047035 537 0.0038456408 110 0.0010902329 324 0.8511971524 538 0.0041251642 111 0.0005832264 325 0.8497805198 539 0.0043801861 112 0.0000276045 326 0.8480315777 540 0.0046039530 113 -0.0005464280 327 0.8459818469 541 0.0048109469 114 -0.0011568135 328 0.8436238281 542 0.0049839687 115 -0.0018039472 329 0.8409541392 543 0.0051382275 116 -0.0024826723 330 0.8379717337 544 0.0052715758 117 -0.0031933778 331 0.8346937361 545 0.0053838975 118 -0.0039401124 332 0.8311038457 546 0.0054753783 119 -0.0047222596 333 0.8272275347 547 0.0055404363 120 -0.0055337211 334 0.8230419890 548 0.0055917128 121 -0.0063792293 335 0.8185776004 549 0.0056266114 122 -0.0072615816 336 0.8138191270 550 0.0056389199 123 -0.0081798233 337 0.8087695004 551 0.0056455196 124 -0.0091325329 338 0.8034485751 552 0.0056220643

- 22 044947

125 -0.0101150215 339 0.7978466413 553 0.0055938023 126 -0.0111315548 340 0.7919735841 554 0.0055475714 127 -0.0121849995 341 0.7858353120 555 0.0054876040 128 0.0132718220 342 0.7794287519 556 0.0054196775 129 0.0143904666 343 0.7727780881 557 0.0053471681 130 0.0155405553 344 0.7658674865 558 0.0052461166 131 0.0167324712 345 0.7587080760 559 0.0051407353 132 0.0179433381 346 0.7513137456 560 0.0050393022 133 0.0191872431 347 0.7436827863 561 0.0049137603 134 0.0204531793 348 0.7358211758 562 0.0047932560 135 0.0217467550 349 0.7277448900 563 0.0046606460 136 0.0230680169 350 0.7194462634 564 0.0045209852 137 0.0244160992 351 0.7109410426 565 0.0043730719 138 0.0257875847 352 0.7022388719 566 0.0042264269 139 0.0271859429 353 0.6933282376 567 0.0040819753 140 0.0286072173 354 0.6842353293 568 0.0039207432 141 0.0300502657 355 0.6749663190 569 0.0037603922 142 0.0315017608 356 0.6655139880 570 0.0036008268 143 0.0329754081 357 0.6559016302 571 0.0034418874 144 0.0344620948 358 0.6461269695 572 0.0032739613 145 0.0359697560 359 0.6361980107 573 0.0031125420 146 0.0374812850 360 0.6261242695 574 0.0029469447 147 0.0390053679 361 0.6159109932 575 0.0027870464 148 0.0405349170 362 0.6055783538 576 0.0026201758 149 0.0420649094 363 0.5951123086 577 0.0024625616 150 0.0436097542 364 0.5845403235 578 0.0023017254 151 0.0451488405 365 0.5738524131 579 0.0021461583 152 0.0466843027 366 0.5630789140 580 0.0019841140 153 0.0482165720 367 0.5522051258 581 0.0018348265 154 0.0497385755 368 0.5412553448 582 0.0016868083 155 0.0512556155 369 0.5302240895 583 0.0015443219 156 0.0527630746 370 0.5191234970 584 0.0013902494 157 0.0542452768 371 0.5079817500 585 0.0012577884 158 0.0557173648 372 0.4967708254 586 0.0011250155

- 23 044947

159 0.0571616450 373 0.4855253091 587 0.0009885988 160 0.0585915683 374 0.4742453214 588 0.0008608443 161 0.0599837480 375 0.4629308085 589 0.0007458025 162 0.0613455171 376 0.4515996535 590 0.0006239376 163 0.0626857808 377 0.4402553754 591 0.0005107388 164 0.0639715898 378 0.4289119920 592 0.0004026540 165 0.0652247106 379 0.4175696896 593 0.0002949531 166 0.0664367512 380 0.4062317676 594 0.0002043017 167 0.0676075985 381 0.3949211761 595 0.0001094383 168 0.0687043828 382 0.3836350013 596 0.0000134949 169 0.0697630244 383 0.3723795546 597 -0.0000617334 170 0.0707628710 384 -0.3611589903 598 -0.0001446380 171 0.0717002673 385 -0.3499914122 599 -0.0002098337 172 0.0725682583 386 -0.3388722693 600 -0.0002896981 173 0.0733620255 387 -0.3278113727 601 -0.0003501175 174 0.0741003642 388 -0.3168278913 602 -0.0004095121 175 0.0747452558 389 -0.3059098575 603 -0.0004606325 176 0.0753137336 390 -0.2950716717 604 -0.0005145572 177 0.0758008358 391 -0.2843214189 605 -0.0005564576 178 0.0761992479 392 -0.2736634040 606 -0.0005946118 179 0.0764992170 393 -0.2631053299 607 -0.0006341594 180 0.0767093490 394 -0.2526480309 608 -0.0006650415 181 0.0768173975 395 -0.2423016884 609 -0.0006917937 182 0.0768230011 396 -0.2320690870 610 -0.0007215391 183 0.0767204924 397 -0.2219652696 611 -0.0007319357 184 0.0765050718 398 -0.2119735853 612 -0.0007530001 185 0.0761748321 399 -0.2021250176 613 -0.0007630793 186 0.0757305756 400 -0.1923966745 614 -0.0007757977 187 0.0751576255 401 -0.1828172548 615 -0.0007801449 188 0.0744664394 402 -0.1733808172 616 -0.0007803664 189 0.0736406005 403 -0.1640958855 617 -0.0007779869 190 0.0726774642 404 -0.1549607071 618 -0.0007834332 191 0.0715826364 405 -0.1459766491 619 -0.0007724848 192 0.0703533073 406 -0.1371551761 620 -0.0007681371

-

Claims (10)

193 0.0689664013 407 -0.1285002850 621 -0.0007490598 194 0.0674525021 408 -0.1200077984 622 -0.0007440941 195 0.0657690668 409 -0.1116826931 623 -0.0007255043 196 0.0639444805 410 -0.1035329531 624 -0.0007157736 197 0.0619602779 411 -0.0955533352 625 -0.0006941614 198 0.0598166570 412 -0.0877547536 626 -0.0006777690 199 0.0575152691 413 -0.0801372934 627 -0.0006540333 200 0.0550460034 414 -0.0726943300 628 -0.0006312493 201 0.0524093821 415 -0.0654409853 629 -0.0006132747 202 0.0495978676 416 -0.0583705326 630 -0.0005870930 203 0.0466303305 417 -0.0514804176 631 -0.0005677802 204 0.0434768782 418 -0.0447806821 632 -0.0005466565 205 0.0401458278 419 -0.0382776572 633 -0.0005226564 206 0.0366418116 420 -0.0319531274 634 -0.0005040714 207 0.0329583930 421 -0.0258227288 635 -0.0004893791 208 0.0290824006 422 -0.0198834129 636 -0.0004875227 209 0.0250307561 423 -0.0141288827 637 -0.0004947518 210 0.0207997072 424 -0.0085711749 638 -0.0005617692 211 0.0163701258 425 -0.0032086896 639 -0.0005525280 212 0.0117623832 426 0.0019765601 213 0.0069636862 427 0.0069636862 The prototype filter, p ₀ (n), can also be derived from the table. 4 through one or more mathematical operations such as rounding, downsampling, interpolation, or decimation. It is understood that, within the scope of the appended claims, the invention may be practiced in a manner other than that specifically described herein. Any reference numbers contained in the following claims are for illustrative purposes only and are not to be used in any way to interpret or limit the claims. CLAIM 1. A method for decoding an encoded audio bitstream, the method comprising the steps of receiving an encoded audio bitstream, the encoded audio bitstream including audio data representing a low frequency band portion of an audio signal; decoding the audio data to generate a decoded audio signal in the low frequency band; extracting high frequency reconstruction metadata from the encoded audio bitstream, the high frequency reconstruction metadata includes operating parameters for a high frequency reconstruction process that converts a number of subbands from the low frequency band portion of the audio signal to the high frequency band portion of the audio signal; extracting from the encoded audio bit stream a parameter indicating whether or not to use a frequency domain adaptive with respect to the resampling signal; filtering the decoded audio signal in the low frequency band with a signal decomposition filter bank to form a filtered audio signal in the low frequency band; extracting from the encoded audio bit stream a flag indicator indicating whether linear transform or harmonic transposition should be performed on the audio data; recovering the high-band portion of the audio signal using the filtered low-band audio signal and high-pass reconstruction metadata in accordance with the flag, and combining the filtered low-band audio signal and the reconstructed high-band portion to generate a wideband audio signal using the filter bank signal synthesis, - 25 044947 wherein the signal decomposition filter bank includes signal decomposition filters, h _k (n), which are modulated versions of the prototype filter, p ₀ (n), according to GL GL ( ^π ( h _k (n) = p ₀ (n) exp i— fc + - η- — IM 2D 0 < n <A; 0 </с < M where p ₀ (n) is a real-valued symmetric or asymmetric prototype filter; M is the number of channels in the signal decomposition filter bank; and N is the order of the prototype filter, and the number of channels in the signal decomposition filter bank differs from the number of channels in the signal synthesis filter bank. 2. The method of claim 1, wherein the encoded audio bitstream also includes a padding element with an identifier indicating the start of the padding element, and padding data after the identifier, wherein the padding data includes a flag indicator. 3. The method according to claim 2, in which the identifier is a three-bit unsigned integer, transmitted most significant bit first and having the value 0x6. 4. The method of claim 2, wherein the padding data includes an extension payload, the extension payload includes spectrum band replication extension data, and the extension payload is identified by a four-bit unsigned integer, most significant bit first, having the value 1101 or 1110, and optionally wherein the spectrum band replication extension data includes an optional spectrum band replication header, spectrum band replication data after the header, a spectrum band replication extension element after the spectrum band replication data, and wherein a flag indicator is included in the extension element replication of spectrum bands. 5. The method according to any one of claims 1 to 4, wherein the high frequency reconstruction metadata includes an operating parameter selected from the group consisting of envelope scale factors, noise floor scale factors, sinusoidal complement information, time information frequency grid, crossover frequency and inverse filtering mode. 6. The method according to any one of claims 1-4, in which the prototype filter, p ₀ (n), is derived from the coefficients in the table. 4. 7. The method according to any one of claims 1-4, in which the prototype filter, p ₀ (n), is derived from the coefficients in the table. 4 through one or more mathematical operations selected from the group consisting of rounding, downsampling, interpolation, or decimation. 8. The method according to any one of claims 1 to 4, wherein the phase shift is added to the filtered low-band audio signal after filtering and compensated before combining. 9. A non-transitory machine-readable medium containing instructions that, when executed by the processor, cause the processor to execute the method of claim 1. 10. A decoder for decoding an encoded audio bitstream, the decoder includes an input interface for receiving an encoded audio bitstream, the encoded audio bitstream includes audio data representing a low frequency band portion of an audio signal; a main decoder for decoding audio data to generate a decoded audio signal in the low frequency band; a parser for extracting high-frequency reconstruction metadata from the encoded audio bitstream; and a parameter indicating whether or not to use the frequency domain adaptive to the resampling signal; high-frequency reconstruction metadata includes operating parameters for a high-frequency reconstruction process that converts a number of subbands from part of the low-frequency band of the audio signal into part of the high-frequency band of the audio signal; a signal decomposition filter bank for filtering the decoded low-band audio signal to generate a filtered low-band audio signal; a parser for extracting from the encoded audio bit stream a flag indicator indicating whether a linear transform or a harmonic transposition is to be performed on the audio data; a high-pass reconstructor for reconstructing the high-band portion of the audio signal using the filtered low-band audio signal and high-pass reconstruction metadata in accordance with the flag; and a signal synthesis filter bank for combining the filtered audio signal in the low frequency band and the reconstructed part of the high frequency band to form a wideband audio signal, -