Audio Encoder Tonality Calculation Complexity Reduction
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Solution Overview
Problem
Current audio coding systems, such as those using Spectral Band Replication (SBR) and Spectral Extension (SPX), face significant computational complexity in determining side information, particularly in tonality calculations, which account for a substantial portion of the encoder's resources.
Innovation Solution
A method is introduced to reduce computational complexity by determining banded tonality values in a two-step approach, where bin tonality values are first calculated and then combined to yield banded tonality values, allowing for reduced data rates and lower computational requirements, especially in high frequency reconstruction techniques like HE-AAC and Dolby Digital Plus.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional tonality calculation methods are used in SPX-based audio encoders, then accurate high frequency reconstruction is achieved, but computational complexity increases significantly
Solution Approach 1:
The patent divides the audio frequency spectrum into multiple subbands (low frequency band and high frequency band), and further divides each band into several subbands. Tonality values are calculated separately for each subband rather than for the entire frequency spectrum, reducing the computational complexity while maintaining accurate tonality measurement for high frequency reconstruction
Solution Approach 2:
The patent calculates tonality values for low frequency subbands in advance (preliminarily) and stores them. These pre-calculated tonality values are then reused when reconstructing high frequency content, avoiding redundant calculations and significantly reducing the computational burden during the encoding process
2Reliability
If high frequency content is directly encoded, then audio quality is maintained, but data rate and transmission resources increase
Solution Approach 1:
The patent copies low frequency subband signals to high frequency subbands and uses tonality information to modify the copied signals. This allows the high frequency content to be reconstructed from low frequency content rather than transmitting separate high frequency data, maintaining audio quality while reducing data rate
Solution Approach 2:
The patent changes the tonality parameter of copied low frequency subbands to match the original high frequency subbands. By adjusting parameters like noise blending factors based on tonality differences, the reconstructed high frequency content achieves perceptual fidelity without requiring direct transmission of high frequency data
Data Source
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AI summary
The present document relates to the technical field of audio coding, decoding and processing. It specifically relates to methods of recovering high frequency content of an audio signal from low frequency content of the same audio signal in an efficient manner. A method for determining a first banded tonality value (311, 312) for a first frequency subband (205) of an audio signal is described. The first banded tonality value (311, 312) is used for approximating a high frequency component of the audio signal based on a low frequency component of the audio signal. The method comprises determining a set of transform coefficients in a corresponding set of frequency bins based on a block of samples of the audio signal; determining a set of bin tonality values (341) for the set of frequency bins using the set of transform coefficients, respectively; and combining a first subset of two or more of the set of bin tonality values (341) for two or more corresponding adjacent frequency bins of the set of frequency bins lying within the first frequency subband, thereby yielding the first banded tonality value (311, 312) for the first frequency subband.