Multichannel Audio Encoding with Side and Residual Gain Quantization
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Solution Overview
Problem
Current methods for lossy parametric encoding of stereo signals at low bitrates, such as those based on parametric stereo in MPEG-4 Part 3, face challenges due to the complexity of calculating and handling parameters like ILD, which can have very small or very large values, leading to inefficiencies in calculation and quantization.
Innovation Solution
A new approach using two gain parameters, a side gain and a residual gain, calculated from the first and second channels of a multichannel signal, which are limited to specific ranges, allowing for efficient calculation and transmission, and enabling a mid/side transformation to capture full information, with the side signal being waveform coded and the residual signal modeled parametrically.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional parametric stereo encoding using ILD, IPD, and ICC parameters is used, then audio quality is maintained, but calculation complexity increases significantly and bit requirements increase
Solution Approach 1:
The patent extracts only the essential spatial information needed for stereo reconstruction by using a simplified parameter set (inter-channel energy difference and inter-channel phase difference) instead of the traditional three parameters (ILD, IPD, ICC). This extraction of core spatial characteristics reduces calculation complexity while maintaining perceptual audio quality.
Solution Approach 2:
The patent changes the parameter representation by using energy difference and phase difference metrics that are computationally more efficient than traditional ILD, IPD, and ICC calculations. The energy difference parameter replaces the need for separate level and coherence calculations, reducing overall computational burden.
2Measurement precision
If ILD parameter with unrestricted value range is used, then spatial accuracy is improved, but quantization efficiency deteriorates
Solution Approach 1:
The patent transforms the ILD parameter into an energy difference metric with a restricted value range, which can be efficiently quantized using fewer bits. The energy difference is calculated as the logarithmic difference between channel energies, naturally constraining the parameter range and improving quantization efficiency while preserving spatial perception.
3Measurement precision
If full stereo parameter set (ILD, IPD, ICC) is transmitted, then spatial reconstruction accuracy is improved, but transmission bitrate increases
Solution Approach 1:
The patent extracts and transmits only the most perceptually relevant spatial parameters (energy difference and phase difference) while omitting less critical parameters. This selective extraction reduces the parameter set size from three parameters to two, lowering transmission bitrate while maintaining spatial reconstruction accuracy that matters most to human perception.
Solution Approach 2:
The patent applies partial action by transmitting a reduced but sufficient parameter set rather than the complete traditional parameter set. The energy difference and phase difference parameters provide just enough spatial information for perceptually accurate reconstruction, avoiding the bitrate cost of transmitting redundant or less perceptually important parameters.
Data Source
AI summary
An apparatus for encoding a multi-channel signal having at least two channels, has: a downmixer for calculating a downmix signal from the multi-channel signal; a parameter calculator for calculating a side gain from a first channel of the at least two channels and a second channel of the at least two channels and for calculating a residual gain from the first channel and the second channel; and an output interface for generating an output signal, the output signal having information on the downmix signal, and on the side gain and the residual gain.