Multichannel Audio Encoding With Bounded Side and Residual Gains
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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 in MPEG-4 Part 3, face challenges with the ILD parameter's wide range of values, leading to complexity issues in calculation and quantization.
Innovation Solution
A new encoding approach using two gain parameters, a side gain and a residual gain, calculated from the mid and side signals of multichannel audio, where the side gain is limited to [-1, 1] and the residual gain to [0, 1], allowing for efficient calculation and quantization, and only the mid signal is waveform coded while the side signal is modeled parametrically.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If ILD parameter is used for parametric stereo encoding, then spatial image information is captured, but calculation and quantization complexity increases due to unrestricted value range
Solution Approach 1:
The patent transforms the ILD parameter with unrestricted value range into a gain parameter with limited range [-1, 1]. This parameter transformation maintains the essential spatial information while enabling efficient quantization and reducing computational complexity. The gain parameter is derived from the relationship between mid and side signals, fundamentally changing the parameter representation from amplitude ratio to normalized gain factor.
2Quantity of substance
If traditional parametric stereo encoding is used, then bitrate is reduced, but handling of gain parameters with wide range becomes problematic
Solution Approach 1:
The invention introduces a normalized gain parameter constrained to the interval [-1, 1], which dramatically improves parameter handling efficiency. This normalized parameter can be efficiently quantized with fewer bits while maintaining encoding accuracy. The gain parameter represents the ratio of side signal energy to mid signal energy in a normalized form, making it computationally tractable and easier to process than traditional ILD parameters.
3Productivity
If side gain and residual gain are limited to finite intervals, then quantization efficiency improves, but representation accuracy may be affected
Solution Approach 1:
The patent normalizes the gain parameter to a finite interval [-1, 1] through mathematical transformation. This normalization enables efficient uniform quantization while preserving the essential relationship between mid and side signals. The bounded parameter space allows for optimized bit allocation and quantization step sizes, improving overall encoding efficiency without sacrificing perceptual accuracy.
Data Source
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AI summary
An apparatus for encoding a multi-channel signal 100 comprising at least two channels 101, 102, comprises: a downmixer 120 for calculating a downmix signal 122 from the multi-channel signal 100; a parameter calculator 140 for calculating a side gain 141 from a first channel 101 of the at least two channels and a second channel 102 of the at least two channels and for calculating a residual gain 142 from the first channel 101 and the second channel 102; and an output interface 160 for generating an output signal, the output signal comprising information on the downmix signal 122, and on the side gain 141 and the residual gain 142.