Phase Decorrelation for Acoustical Crosstalk Reduction
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Solution Overview
Problem
Acoustical crosstalk between loudspeakers leads to phantom center images with undesirable coloration and reduced speech intelligibility, particularly when multiple listeners are in arbitrary positions, as existing solutions either require additional speakers or are effective only within a limited 'sweet spot' due to varying frequency notches with listener position.
Innovation Solution
The method employs phase decorrelation by separating input signals into high and low frequencies, processing high frequencies with non-identical allpass filters to create frequency-dependent delays, and combining these with delayed low-frequency signals to produce a stereo response, effectively diffusing phase differences and minimizing comb filtering effects across the frequency spectrum.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a real center speaker is added to eliminate phantom center image issues, then center image stability is improved, but device complexity and cost increase
Solution Approach 1:
The patent creates a virtual center speaker by processing signals through digital filters and delay elements that simulate the acoustic response of a physical center speaker. The left and right channel signals are filtered and delayed to create a phantom center image that behaves like a real speaker without requiring additional hardware.
Solution Approach 2:
The patent replaces the mechanical solution of adding a physical center speaker with a digital signal processing approach. By using FIR filters, IIR filters, and delay elements in the audio processing circuitry, the system achieves center speaker functionality through electronic manipulation rather than mechanical addition.
2Loss of information
If crosstalk cancellation techniques are used to eliminate comb filtering effects, then speech intelligibility is improved, but the solution is limited to a small 'sweet spot' area
Solution Approach 1:
The patent applies preliminary filtering and delay adjustments to the left and right channel signals before they reach the speakers. By pre-processing the signals with specific FIR and IIR filters and delay elements, the system anticipates and compensates for crosstalk effects across a wider area, creating a more robust phantom center image that remains stable for listeners in various positions rather than requiring precise cancellation at a single point.
3Stability of the object's composition
If inverse filters are applied to equalize magnitude response, then frequency response flatness is improved, but manufacturing precision requirements increase due to position-dependent notch frequencies
Solution Approach 1:
The patent changes the approach from position-dependent inverse filtering to position-independent filter design. By using FIR filters with coefficients designed to create a flat frequency response regardless of listener position, and IIR filters with adjustable parameters that can be tuned for different configurations, the system achieves frequency response equalization without requiring precise knowledge of speaker and listener positions.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach results in a flatter magnitude response, reducing the perception of phantom center image issues and enhancing speech intelligibility by randomizing phase cancellations within critical bands, while preserving localization cues at lower frequencies and improving headphone compatibility.
Implementation Method 1
phase decorrelation to minimize the effects of acoustical crosstalk
Implementation Method 2
The high-frequency signal is processed using a diffusion means, such as an allpass filter, creating a high-frequency left channel signal
Data Source
AI summary
When two loudspeakers play the same signal, a “phantom center” image is produced between the speakers. However, this image differs from one produced by a real center speaker. In particular, acoustical crosstalk produces a comb-filtering effect, with cancellations that may be in the frequency range needed for the intelligibility of speech. Methods for using phase decorrelation to fill in these gaps and produce a flatter magnitude response are described, reducing coloration and potentially enhancing dialogue clarity. These methods also improve headphone compatibility and reduce the tendency of the phantom image to move toward the nearest speaker.