Multichannel Audio Encoding with Side and Residual Gain Parameters
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Solution Overview
Problem
Existing methods for lossy parametric encoding of stereo signals at low bitrates, such as those based on parametric stereo as standardized in MPEG-4 Part 3, face significant complexity issues due to the wide range of values for parameters like ILD, which complicates calculation, quantization, and handling.
Innovation Solution
The proposed solution involves a new parametric encoding procedure that uses two gain parameters: a side gain parameter and a residual gain parameter. These gain parameters are calculated from the first and second channels of a multichannel signal and are limited to specific ranges, reducing complexity and improving efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If traditional parametric stereo encoding is used with ILD, IPD, and ICC parameters, then stereo signal encoding is achieved, but calculation and handling complexity increases significantly
Solution Approach 1:
The patent transforms the traditional ILD parameter with unrestricted range into a side gain parameter with limited range [-1, +1]. This parameter transformation resolves the contradiction by changing the mathematical representation from logarithmic scale to a bounded gain factor, enabling efficient quantization and calculation while preserving the essential stereo information.
Solution Approach 2:
The patent segments the stereo encoding into two independent gain parameters (side gain and residual gain) instead of using traditional correlated parameters. This segmentation allows each parameter to be calculated and quantized independently with controlled ranges, reducing the overall computational complexity while maintaining encoding precision.
2Ease of operation
If ILD parameter is used with very small or very big values, then full dynamic range is captured, but efficient calculation and quantization becomes problematic
Solution Approach 1:
The patent applies parameter transformation by converting ILD from a logarithmic ratio with unrestricted range to a linear gain factor bounded in [-1, +1]. This change enables uniform quantization steps and efficient digital representation without losing the ability to represent the full dynamic range of stereo signals through the bounded gain parameter.
3Device complexity
If mid/side transformation with two gain parameters is used, then encoding complexity is reduced, but new parameter calculation methods are required
Solution Approach 1:
The patent introduces mid/side transformation as an intermediary step that decouples the stereo encoding into independent gain calculations. By transforming to the mid-side domain first, the subsequent gain parameter calculations become simpler and more straightforward, reducing overall encoding complexity while providing a systematic implementation framework.
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.