Band-Wise Audio Downmixing to Avoid Phase Cancellation
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Solution Overview
Problem
Existing methods for stereo-to-mono downmixing in audio signal processing face challenges such as phase cancellation effects, energy loss, and increased complexity and delay, especially in mobile communication scenarios like the 3GPP IVAS standard.
Innovation Solution
A downmixer that estimates band-wise weighting values to weight spectral domain representations of audio channels, converting these weighted representations into time domain, and then mixing them to produce a downmix signal, while maintaining individual channel processing flexibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a passive downmix is used to convert stereo signal to mono, then the processing complexity is low, but phase cancellation effects and energy loss occur degrading audio quality
Solution Approach 1:
The downmixing process is segmented into multiple stages: spectral domain analysis, band-wise weighting calculation, frequency-dependent weighting application, and time-domain synthesis. This segmentation allows complex audio quality preservation operations to be broken down into manageable steps that can be efficiently implemented
Solution Approach 2:
The patent applies frequency-dependent weighting parameters to different spectral bands of the stereo channels. By calculating optimal weighting values for each frequency band and applying them before downmixing, the system preserves energy and avoids phase cancellation while maintaining low computational complexity through efficient parameter optimization
2Reliability
If active downmixing methods with energy correction are used, then audio quality improves, but processing complexity and delay increase
Solution Approach 1:
The patent replaces complex time-domain energy correction operations with frequency-domain weighting operations. By performing the downmixing in the spectral domain where energy distribution can be efficiently analyzed and adjusted through simple multiplication with weighting factors, the system achieves energy preservation without the computational burden of iterative time-domain optimization
Solution Approach 2:
The system calculates optimal weighting parameters for each frequency band based on the spectral content of the stereo channels. These parameters are then applied to weight the spectral components before downmixing, achieving energy correction through efficient parameter-based control rather than complex mechanical processing
3Reliability
If band-wise downmixing is performed in frequency domain, then energy preservation and phase alignment improve, but processing delay and complexity increase
Solution Approach 1:
The patent substitutes complex iterative frequency-domain optimization processes with direct spectral weighting operations. By calculating weighting factors from the spectral representation and applying them through simple multiplication, the system achieves energy preservation and phase alignment without requiring multiple iterative passes or complex transformations that would increase processing delay
Data Source
AI summary
A downmixer for downmixing a multi-channel signal having at least two channels, includes: a weighting value estimator for estimating band-wise weighting values for the at least two channels; a spectral weighter for weighting spectral domain representations of the at least two channels using the band-wise weighting values; a converter for converting weighted spectral domain representations of the at least two channels into time representations of the at least two channels; and a mixer for mixing the time representations of the at least two channels to obtain a downmix signal.