Stereo Downmix Phase Compensation for Low-Bitrate Encoding
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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 with the ILD parameter's wide range of values, leading to complexity issues in calculation and quantization.
Innovation Solution
The proposed solution introduces a new mid/side approach using two gain parameters, side gain, and residual gain, which are calculated and transmitted instead of ILD and ICC, allowing for efficient encoding and decoding with absolute phase compensation, limiting the side gain to [-1, 1] and residual gain to [0, 1], and calculating these parameters in the spectral domain.
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 phase difference parameter with a limited range of [-0.5, 0.5] cycles. This parameter transformation resolves the contradiction by maintaining the spatial image information while enabling efficient quantization and calculation with a bounded parameter space.
2Quantity of substance
If traditional parametric stereo encoding is used, then bitrate reduction is achieved, but handling of phase differences becomes problematic
Solution Approach 1:
The patent changes the parameter representation from ILD (with problematic unrestricted range) to phase difference parameters normalized to [-0.5, 0.5] cycles. This enables efficient bitrate reduction through compact quantization while simplifying the handling of phase differences in the encoding and decoding processes.
Data Source
AI summary
An apparatus for downmixing a multi-channel signal having at least two channels, has: a downmixer for calculating a downmix signal from the multi-channel signal, wherein the downmixer is configured to calculate the downmix using an absolute phase compensation, so that a channel having a lower energy among the at least two channels is only rotated or is rotated stronger than a channel having a greater energy in calculating the downmix signal; and an output interface for generating an output signal, the output signal having information on the downmix signal.