Stereo Signal Down-Mixing Phase Difference Calculation
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Solution Overview
Problem
Current stereo signal down-mixing methods fail to accurately restore left and right channel signals when phases are completely reverse and amplitudes are the same, leading to energy loss and poor sound field representation.
Innovation Solution
A method that converts stereo signals into frequency-domain signals, calculates frequency-domain channel signal level and phase differences, and uses these to determine a down-mixed signal phase located between the phases of the left and right channel signals, ensuring accurate amplitude calculation and energy preservation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If traditional down-mixing methods (simple averaging or frequency-domain amplitude adjustment) are used, then the encoding process is simple, but energy loss occurs and the down-mixed signal cannot accurately restore the original stereo signals when phases are completely reverse
Solution Approach 1:
The patent changes the parameters used in down-mixing from simple amplitude weighting to a more sophisticated approach that incorporates both amplitude and phase information. By calculating the phase difference between left and right channels and using it to determine the down-mixed signal phase, the method preserves energy that would otherwise be lost in traditional averaging methods, especially when channels have opposite phases.
Solution Approach 2:
The patent introduces phase difference as an intermediary parameter that mediates between the left and right channel signals. Instead of directly averaging the channels, the method first calculates the phase difference, uses it to determine the appropriate down-mixed phase, and then combines the channels. This intermediary step prevents energy loss while maintaining relatively simple processing.
2Loss of information
If traditional down-mixing methods are used, then the encoding process is simple, but the down-mixed signal fails to accurately represent the sound field features of the stereo signal
Solution Approach 1:
The patent changes from ignoring phase information to explicitly utilizing phase difference as a key parameter. By calculating the phase difference between channels and using it to determine the down-mixed signal phase, the method preserves sound field information that would be lost in traditional amplitude-only approaches, enabling more accurate restoration of the original stereo signals.
Solution Approach 2:
The patent implements a feedback mechanism where the phase difference calculated from the left and right channels is fed back into the down-mixing process to determine the down-mixed signal phase. This feedback loop ensures that the down-mixed signal accurately reflects the spatial relationship between channels, preserving sound field features while maintaining a relatively simple processing structure.
3Reliability
If frequency-domain phase adjustment is used with a benchmark channel, then the down-mixed signal phase can be controlled, but when the benchmark channel is noise or has large phase changes, the down-mixed signal phase encounters large jumps and becomes unstable
Solution Approach 1:
The patent applies local quality by treating different frequency regions differently. Instead of using a single benchmark channel approach that is vulnerable to noise, the method calculates phase difference locally for each frequency bin. This localized approach ensures that noise in one frequency range does not affect the phase determination in other ranges, improving overall stability.
Solution Approach 2:
The patent uses partial action by calculating phase difference only for frequency bins where the signal is sufficiently strong. For frequency bins with low energy or high noise content, the method avoids using those bins for phase determination, thereby preventing large phase jumps caused by noisy benchmark channels while still maintaining accurate phase control for reliable frequency bins.
Data Source
AI summary
Embodiments of the present invention provide a stereo signal down-mixing method, encoding/decoding apparatus and system. The down-mixing method includes: converting a first channel time-domain signal and a second channel time-domain signal into a first channel frequency-domain signal and a second channel frequency-domain signal; obtaining a frequency-domain channel signal level difference and a frequency-domain channel signal phase difference between the two channel frequency-domain signals; for each frequency bin in each frequency band, using a function based on the frequency-domain channel signal level difference and frequency-domain channel signal phase difference to obtain a down-mixed signal phase that is located between phases of the two channel frequency-domain signals, and obtaining a down-mixed signal amplitude through calculation; and obtaining a frequency-domain down-mixed signal according to the phase and amplitude.