Audio Codec Transform Length Switching for Transient Signals
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Solution Overview
Problem
Existing frequency-domain audio coding systems face challenges in achieving satisfactory quality for audio signals with prominent transients, such as rain or applause, at low bitrates, due to issues like time-smearing and inefficiencies in long or short block coding.
Innovation Solution
A frequency-domain audio codec is enhanced to support switching between different transform lengths, allowing for interleaved transmission of frequency-domain coefficients, independent of signalization, to maintain backward compatibility and improve coding efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If long block coding is used, then spectral resolution is improved, but temporal resolution deteriorates causing time-smearing and pre-echo
Solution Approach 1:
The audio signal is divided into multiple blocks of different lengths (short, medium, long) allowing the system to segment the processing into appropriate temporal and spectral resolutions for different signal characteristics
2Manufacturing precision
If short block coding is used, then temporal resolution is improved, but spectral resolution deteriorates and data overhead increases
Solution Approach 1:
The block length is dynamically adjusted based on the temporal stationarity of the signal, allowing the system to switch between short, medium, and long blocks to optimize both spectral and temporal resolution for different audio content
3Adaptability or versatility
If a new transform length is added to existing codecs, then adaptability is improved, but device complexity increases
Solution Approach 1:
The interleaving mechanism allows the same transmission structure to carry both traditional long-block coefficients and new medium-block coefficients, enabling existing decoders to process the bitstream while enhanced decoders can utilize the additional transform length option
4Productivity
If transform length switching is implemented, then coding efficiency is improved, but device complexity increases
Solution Approach 1:
The frequency-domain coefficients are pre-arranged in an interleaved pattern during encoding, which simplifies the decoding process by allowing straightforward extraction and processing without complex reorganization operations
Data Source
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AI summary
A frequency-domain audio codec is provided with the ability to additionally support a certain transform length in a backward-compatible manner, by the following: the frequency-domain coefficients of a respective frame are transmitted in an interleaved manner irrespective of the signalization signaling for the frames as to which transform length actually applies, and additionally the frequency-domain coefficient extraction and the scale factor extraction operate independent from the signalization. By this measure, old-fashioned frequency-domain audio coders/decoders, insensitive for the signalization, would be able to nevertheless operate without faults and with reproducing a reasonable quality. Concurrently, frequency-domain audio coders/decoders able to support the additional transform length would offer even better quality despite the backward compatibility. As far as coding efficiency penalties due to the coding of the frequency domain coefficients in a manner transparent for older decoders are concerned, same are of comparatively minor nature due to the interleaving.