Multichannel Downmixing with Dynamic Coefficients for Direction Preservation
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Solution Overview
Problem
Conventional downmixers fail to preserve the intended direction and signal energy of multichannel audio signals when converting them to two-channel outputs, often resulting in loss of directional information and reduced loudness, especially in the presence of reverberation and sound events.
Innovation Solution
A downmixer system that generates mix coefficients based on energy comparisons between input and output signals, using a test downmixer environment to determine coefficients that preserve signal energy and direction, and adjusts these coefficients to emphasize sound events and accurately represent reverberation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If fixed mix coefficients are used in conventional downmixers, then the downmixing process is simple and stable, but the intended direction and signal energy of the multichannel signal are not preserved
Solution Approach 1:
The patent applies dynamics by transitioning from fixed mix coefficients to dynamic mix coefficients that are continuously adapted based on the correlation between input channels. The system monitors the correlation coefficient in real-time and adjusts the mix coefficients accordingly, allowing the downmixer to adapt its behavior to the specific characteristics of the input signal while maintaining a relatively simple overall structure.
Solution Approach 2:
The patent changes the parameter of mix coefficients from static to dynamic values. By calculating the correlation coefficient between input channels and using it to modulate the mix coefficients, the system preserves signal energy and directional information without requiring a completely complex redesign of the downmixing architecture.
2Loss of energy
If rear channels are attenuated by 3 dB before mixing, then the downmixing process is simplified, but the loudness of sound effects in rear channels is reduced and energy is not preserved
Solution Approach 1:
The patent changes the attenuation parameter from a fixed 3 dB reduction to a dynamic adjustment based on correlation coefficients. When channels are highly correlated, less attenuation is applied to preserve energy; when less correlated, more attenuation is applied to maintain simplicity. This adaptive approach preserves signal energy while keeping the process relatively simple.
Solution Approach 2:
The system uses feedback by continuously monitoring the correlation between input channels and adjusting the attenuation level accordingly. The correlation coefficient serves as a feedback signal that determines the appropriate amount of attenuation to apply, ensuring energy preservation when needed while maintaining operational simplicity when possible.
3Loss of information
If rear channels are mixed in antiphase, then the downmixing process is simplified, but directional information about left rear vs right rear is lost
Solution Approach 1:
The patent applies dynamics by making the phase relationship between rear channels adaptive rather than fixed. The system calculates correlation coefficients that capture the directional relationships in the input signal and uses these to dynamically adjust the mixing phase, preserving directional information while maintaining algorithmic simplicity through correlation-based control.
Solution Approach 2:
The patent changes the phase parameter from a fixed antiphase relationship to a dynamic phase relationship determined by correlation coefficients. This allows the system to preserve directional information by adapting the phase shift to match the actual spatial relationships in the multichannel signal while keeping the overall algorithm relatively simple.
4Reliability
If downmixing algorithms are used in the presence of reverberation, then the downmixing process is straightforward, but sound events are reduced in emphasis and may become inaudible
Solution Approach 1:
The patent uses feedback by continuously monitoring the correlation between input channels and using this information to adjust mix coefficients in real-time. This feedback mechanism allows the system to identify and emphasize sound events even in the presence of reverberation, as the correlation-based approach can distinguish between direct sound and reverberant energy, maintaining sound event audibility without requiring complex algorithms.
Data Source
AI summary
A downmixer provides a listener of an output signal with a substantially accurate rendition of the apparent direction and relative loudness of an input signal. Downmixing certain channels of the input signal independently may substantially preserve the energy and intended direction of the input signal. The downmixer may include a test downmixer that operates over a limited frequency range to more accurately reflect the loudness of the input signal at the output, as perceived by a listener. The downmixer may demand fewer resources, freeing up resources for use in other operations.