Stereo Audio Coding with Channel Alignment for MS Downmix
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Solution Overview
Problem
In audio signal encoding, temporal mismatches between multiple microphones lead to misalignment of audio signals, reducing the efficiency of stereo coding techniques like Mid-Side (MS) and Parametric Stereo (PS), resulting in decreased coding gains due to comparable energies in sum and difference channels.
Innovation Solution
A device and method that perform transform operations on reference and target audio channels to determine inter-channel mismatch values, adjust the target channel to align with the reference channel, and encode the mid and side channels, along with a residual channel, to mitigate temporal misalignment and enhance coding efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If stereo encoding is performed on audio signals from multiple microphones, then coding efficiency is improved, but temporal misalignment between channels increases due to different distances from sound source
Solution Approach 1:
The patent applies preliminary action by estimating the inter-channel mismatch value before performing stereo encoding. The encoder determines the temporal misalignment between first and second audio signals from multiple microphones, and adjusts the encoding process accordingly. This preliminary estimation and adjustment of temporal mismatch allows the system to maintain temporal alignment precision while preserving coding efficiency, as the encoding parameters are optimized based on the pre-determined mismatch characteristics
2Adaptability or versatility
If transform operations are performed on audio channels to generate frequency-domain signals, then coding flexibility is improved, but inter-harmonic noise increases due to window mismatch
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the transform parameters based on the estimated inter-channel mismatch value. The encoder modifies window functions, transform lengths, or frequency bin assignments according to the measured temporal misalignment. This adaptive parameter adjustment reduces inter-harmonic noise that would otherwise be generated by fixed window mismatch, while preserving the coding flexibility needed for different audio content types and microphone configurations
Data Source
AI summary
A device includes a processor that is configured to determine an inter-channel mismatch value indicative of a temporal misalignment between a frequency-domain reference channel and a frequency-domain target channel. The processor is also configured to adjust the frequency-domain target channel based on the inter-channel mismatch value to generate an adjusted frequency-domain target channel. The processor is further configured to perform a down-mix operation, based on the frequency-domain reference channel and the adjusted frequency-domain target channel, to generate a mid channel and a side channel. The processor is also configured to generate a predicted side channel based on the mid channel. The processor is further configured to generate a residual channel based on the side channel and the predicted side channel. The processor is also configured to encode the residual channel as part of a bitstream.