UNLIMITED FREE ACCESS TO THE WORLD'S BEST IDEAS

close
Already an Engineering360 user? Log in.

This is embarrasing...

An error occurred while processing the form. Please try again in a few minutes.

Customize Your Engineering360 Experience

close
Privacy Policy

This is embarrasing...

An error occurred while processing the form. Please try again in a few minutes.

ISO/IEC 13818-7

Information technology - Generic coding of moving pictures and associated audio information - Part 7: Advanced Audio Coding (AAC) TECHNICAL CORRIGENDUM 1

active, Most Current
Buy Now
Organization: ISO
Publication Date: 15 April 2009
Status: active
Page Count: 4
ICS Code (Information coding): 35.040
scope:

General

This International Standard describes the MPEG-2 audio non-backwards compatible standard called MPEG-2 Advanced Audio Coding, AAC [1], a higher quality multichannel standard than achievable while requiring MPEG-1 backwards compatibility. This MPEG-2 AAC audio standard allows for ITU-R "indistinguishable" quality according to [2] at data rates of 320 kbit/s for five full-bandwidth channel audio signals.

The AAC decoding process makes use of a number of required tools and a number of optional tools. Table 1 lists the tools and their status as required or optional. Required tools are mandatory in any possible profile. Optional tools may not be required in some profiles.

MPEG-2 AAC Tools Overview

The basic structure of the MPEG-2 AAC system is shown in Figure 1 and Figure 2. As is shown in Table 1, there are both required and optional tools in the decoder. The data flow in this diagram is from left to right, top to bottom. The functions of the decoder are to find the description of the quantized audio spectra in the bitstream, decode the quantized values and other reconstruction information, reconstruct the quantized spectra, process the reconstructed spectra through whatever tools are active in the bitstream in order to arrive at the actual signal spectra as described by the input bitstream, and finally convert the frequency domain spectra to the time domain, with or without an optional gain control tool. Following the initial reconstruction and scaling of the spectrum reconstruction, there are many optional tools that modify one or more of the spectra in order to provide more efficient coding. For each of the optional tools that operate in the spectral domain, the option to "pass through" is retained, and in all cases where a spectral operation is omitted, the spectra at its input are passed directly through the tool without modification.

The input to the bitstream demultiplexer tool is the MPEG-2 AAC bitstream. The demultiplexer separates the parts of the MPEG-AAC data stream into the parts for each tool, and provides each of the tools with the bitstream information related to that tool.

The outputs from the bitstream demultiplexer tool are:

• The sectioning information for the noiselessly coded spectra,

• The noiselessly coded spectra,

• The M/S decision information (optional),

• The predictor state information (optional),

• The intensity stereo control information and coupling channel control information (both optional),

• The temporal noise shaping (TNS) information (optional),

• The filterbank control information, and

• The gain control information (optional).

The noiseless decoding tool takes information from the bitstream demultiplexer, parses that information, decodes the Huffman coded data, and reconstructs the quantized spectra and the Huffman and DPCM coded scalefactors.

The inputs to the noiseless decoding tool are:

• The sectioning information for the noiselessly coded spectra, and

• The noiselessly coded spectra.

The outputs of the Noiseless Decoding tool are:

• The decoded integer representation of the scalefactors, and

• The quantized values for the spectra.

The inverse quantizer tool takes the quantized values for the spectra, and converts the integer values to the non-scaled, reconstructed spectra. This quantizer is a non-uniform quantizer.

The input to the Inverse Quantizer tool is:

• The quantized values for the spectra.

The output of the inverse quantizer tool is:

• The un-scaled, inversely quantized spectra.

The rescaling tool converts the integer representation of the scalefactors to the actual values, and multiplies the un-scaled inversely quantized spectra by the relevant scalefactors.

The inputs to the rescaling tool are:

• The decoded integer representation of the scalefactors, and

• The un-scaled, inversely quantized spectra.

The output from the scalefactors tool is:

• The scaled, inversely quantized spectra.

The M/S tool converts spectra pairs from Mid/Side to Left/Right under control of the M/S decision information in order to improve coding efficiency.

The inputs to the M/S tool are:

• The M/S decision information, and

• The scaled, inversely quantized spectra related to pairs of channels.

The output from the M/S tool is:

• The scaled, inversely quantized spectra related to pairs of channels, after M/S decoding.

Note The scaled, inversely quantized spectra of individually coded channels are not processed by the M/S block, rather they are passed directly through the block without modification. If the M/S block is not active, all spectra are passed through this block unmodified.

The prediction tool reverses the prediction process carried out at the encoder. This prediction process reinserts the redundancy that was extracted by the prediction tool at the encoder, under the control of the predictor state information. This tool is implemented as a second order backward adaptive predictor. The inputs to the prediction tool are:

• The predictor state information, and

• The scaled, inversely quantized spectra.

The output from the prediction tool is:

• The scaled, inversely quantized spectra, after prediction is applied.

Note If the prediction is disabled, the scaled, inversely quantized spectra are passed directly through the block without modification.

The intensity stereo tool implements intensity stereo decoding on pairs of spectra.

The inputs to the intensity stereo tool are:

• The inversely quantized spectra, and

• The intensity stereo control information.

The output from the intensity stereo tool is:

• The inversely quantized spectra after intensity channel decoding.

Note The scaled, inversely quantized spectra of individually coded channels are passed directly through this tool without modification, if intensity stereo is not indicated. The intensity stereo tool and M/S tool are arranged so that the operation of M/S and intensity stereo are mutually exclusive on any given scalefactor band and group of one pair of spectra.

The coupling tool for dependently switched coupling channels adds the relevant data from dependently switched coupling channels to the spectra, as directed by the coupling control information.

The inputs to the coupling tool are:

• The inversely quantized spectra, and

• The coupling control information.

The output from the coupling tool is:

• The inversely quantized spectra coupled with the dependently switched coupling channels.

Note The scaled, inversely quantized spectra are passed directly through this tool without modification, if coupling is not indicated. Depending on the coupling control information, dependently switched coupling channels might either be coupled before or after the TNS processing.

The coupling tool for independently switched coupling channels adds the relevant data from independently switched coupling channels to the time signal, as directed by the coupling control information.

The inputs to the coupling tool are:

• The time signal as output by the filterbank, and

• The coupling control information.

The output from the coupling tool is:

• The time signal coupled with the independently switched coupling channels.

Note The time signal is passed directly through this tool without modification, if coupling is not indicated.

The temporal noise shaping (TNS) tool implements a control of the fine time structure of the coding noise. In the encoder, the TNS process has flattened the temporal envelope of the signal to which it has been applied. In the decoder, the inverse process is used to restore the actual temporal envelope(s), under control of the TNS information. This is done by applying a filtering process to parts of the spectral data.

The inputs to the TNS tool are:

• The inversely quantized spectra, and

• The TNS information.

The output from the TNS block is:

• The inversely quantized spectra.

Note If this block is disabled, the inversely quantized spectra are passed through without modification.

The filterbank / block switching tool applies the inverse of the frequency mapping that was carried out in the encoder. An inverse modified discrete cosine transform (IMDCT) is used for the filterbank tool. The IMDCT can be configured to support either one set of 128 or 1024, or four sets of 32 or 256 spectral coefficients.

The inputs to the filterbank tool are:

• The inversely quantized spectra, and

• The filterbank control information.

The output(s) from the filterbank tool is (are):

• The time domain reconstructed audio signal(s).

When present, the gain control tool applies a separate time domain gain control to each of four frequency bands that have been created by the gain control PQF filterbank in the encoder. Then, it assembles four frequency bands and reconstructs the time waveform through the gain control tool's filterbank.

The inputs to the gain control tool are:

• The time domain reconstructed audio signal(s), and

• The gain control information.

The output(s) from the gain control tool is (are):

• The time domain reconstructed audio signal(s).

If the gain control tool is not active, the time domain reconstructed audio signal(s) are passed directly from the filterbank tool to the output of the decoder. This tool is used for the scalable sampling rate (SSR) profile only.

Document History

December 1, 2010
Information technology - Generic coding of moving pictures and associated audio information - Part 7: Advanced Audio Coding (AAC) TECHNICAL CORRIGENDUM 2
General This International Standard describes the MPEG-2 audio non-backwards compatible standard called MPEG-2 Advanced Audio Coding, AAC [1], a higher quality multichannel standard than achievable...
ISO/IEC 13818-7
April 15, 2009
Information technology - Generic coding of moving pictures and associated audio information - Part 7: Advanced Audio Coding (AAC) TECHNICAL CORRIGENDUM 1
General This International Standard describes the MPEG-2 audio non-backwards compatible standard called MPEG-2 Advanced Audio Coding, AAC [1], a higher quality multichannel standard than achievable...
November 15, 2007
Information technology - Generic coding of moving pictures and associated audio information - Part 7: Advanced Audio Coding (AAC) AMENDMENT 1: Transport of MPEG Surround in AAC
General This International Standard describes the MPEG-2 audio non-backwards compatible standard called MPEG-2 Advanced Audio Coding, AAC [1], a higher quality multichannel standard than achievable...
January 15, 2006
Information technology - Generic coding of moving pictures and associated audio information - Part 7: Advanced Audio Coding (AAC)
General This International Standard describes the MPEG-2 audio non-backwards compatible standard called MPEG-2 Advanced Audio Coding, AAC [1], a higher quality multichannel standard than achievable...
August 15, 2005
Information technology - Generic coding of moving pictures and associated audio information - Part 7: Advanced Audio Coding (AAC) TECHNICAL CORRIGENDUM 1
A description is not available for this item.
October 15, 2004
Information technology - Generic coding of moving pictures and associated audio information - Part 7: Advanced Audio Coding (AAC)
A description is not available for this item.
February 1, 2004
Information technology - Generic coding of moving pictures and associated audio information - Part 7: Advanced Audio Coding (AAC) AMENDMENT 1 : Embedding of bandwidth extension
A description is not available for this item.
August 1, 2003
Information Technology - Generic Coding of Moving Pictures and Associated Audio Information - Part 7: Advanced Audio Coding (AAC)
A description is not available for this item.
December 1, 1998
Information technology - Generic coding of moving pictures and associated audio information - Part 7: Advanced Audio Coding (AAC) TECHNICAL CORRIGENDUM 1
A description is not available for this item.
December 1, 1997
Information Technology - Generic Coding of Moving Pictures and Associated Audio Information - Part 7: Advanced Audio Coding (AAC)
A description is not available for this item.

References

Advertisement