Multi-channel Audio Encoder Smart Averaging ITD Estimation
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Solution Overview
Problem
Current parametric stereo coding methods face challenges in achieving low bitrate and low complexity while maintaining stable inter-aural time difference (ITD) estimation, particularly in mobile terminal applications where battery life is a concern and the complexity of existing algorithms is high.
Innovation Solution
The proposed solution involves smart averaging of inter-channel differences, such as ITD and IPD, between band-limited signal portions of audio channel signals, which reduces bitrate and computational complexity while maintaining stability in ITD estimation by discriminating differences based on their sign.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of information
If time domain cross correlation method is used for ITD estimation, then bitrate is low (only one full band ITD transmitted), but computational complexity is very high
Solution Approach 1:
The patent divides the full-band signal into multiple frequency sub-bands and performs ITD estimation separately for each sub-band. This segmentation allows the use of efficient frequency-domain methods (FFT-based cross-spectrum analysis) for each sub-band, reducing overall computational complexity compared to time-domain cross-correlation on the full-band signal, while maintaining low bitrate by selecting only the most relevant ITD values for transmission.
2Device complexity
If frequency domain ITD estimation is performed for each sub-band, then computational complexity is reduced, but bitrate overhead increases (one ITD per sub-band must be transmitted)
Solution Approach 1:
The patent applies local quality by performing ITD estimation at different resolutions for different sub-bands. Instead of uniformly estimating ITD for all sub-bands, the method selectively estimates ITD only for sub-bands that contain relevant audio information (e.g., sub-bands with significant energy or those containing speech frequencies). This approach reduces bitrate overhead by transmitting ITD parameters only where necessary, while maintaining low computational complexity through the frequency-domain approach.
3Loss of information
If only one full band ITD is estimated, then bitrate is minimized, but stability of ITD estimation becomes difficult to achieve
Solution Approach 1:
The patent introduces dynamics by adaptively selecting ITD values based on the characteristics of each sub-band. The method dynamically determines which sub-bands require ITD estimation based on signal energy, speech activity, or other relevance criteria. This dynamic approach improves stability by focusing ITD estimation resources on the most relevant frequency regions, avoiding unstable estimates in sub-bands where ITD is not meaningful, while maintaining low bitrate by not transmitting ITD for all sub-bands uniformly.
Data Source
AI summary
The invention relates to a method for determining an encoding parameter for an audio channel signal of a multi-channel audio signal, the method comprising: determining a frequency transform of the audio channel signal; determining a frequency transform of a reference audio signal; determining inter channel differences for at least each frequency sub-band of a subset of frequency sub-bands, each inter channel difference indicating a phase difference or time difference between a band-limited signal portion of the audio channel signal and a band-limited signal portion of the reference audio signal in the respective frequency sub-band the inter-channel difference is associated to; determining a first average based on positive values of the inter-channel differences and determining a second average based on negative values of the inter-channel differences; and determining the encoding parameter based on the first average and on the second average.