Audio Matrix Decoder Phantom Image Accuracy
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Solution Overview
Problem
Existing audio matrix decoders face challenges in accurately panning stereo signals to front and rear directions, particularly when signals are encoded with out-of-phase rear-center positions, leading to poor phantom image formation during playback with headphone or loudspeaker virtualizers.
Innovation Solution
The method involves modifying stereo signal pairs by forming a difference signal, scaling it with a bias gain factor, and summing it back into both signals to adjust their amplitudes and polarities, allowing for precise panning to front or rear directions, with greater shifting at rear-center positions to avoid image mislocation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If stereo signals are directly decoded by existing audio matrix decoders, then the decoding process is simple, but the phantom image formation is poor especially for rear-center encoded signals
Solution Approach 1:
The patent applies preliminary action by modifying the stereo signal pair Lt, Rt before decoding to pre-correct for rear-center image formation issues. The signal modification process includes forming difference signals, applying bias gain factors, and adjusting amplitudes and polarities in advance, so that the subsequent decoding produces accurate phantom images without requiring complex post-processing.
Solution Approach 2:
The patent employs parameter changes by dynamically adjusting signal parameters (amplitudes and polarities) based on the encoded direction. The system modifies Lt and Rt signals using bias gain factors that are applied selectively depending on whether signals are encoded for front or rear directions, thereby optimizing phantom image formation for different spatial positions.
2Measurement precision
If signals are panned to rear directions using conventional methods, then the panning function is straightforward, but image mislocation occurs particularly at rear-center positions
Solution Approach 1:
The patent applies local quality by implementing direction-specific signal modification. Different processing is applied to signals depending on their encoded direction: front-center signals receive different treatment than rear-center signals. The bias gain factors and modification operations are locally adapted to the specific spatial position being decoded, ensuring accurate image formation for each direction.
Solution Approach 2:
The system performs preliminary action by pre-adjusting signal parameters before the panning operation. By modifying Lt and Rt signals in advance with appropriate bias gain factors, the system ensures that subsequent panning to rear directions produces accurate spatial positioning without requiring complex real-time adjustments during decoding.
3Adaptability or versatility
If the decoder structure is kept simple, then the device complexity is low, but the ability to dynamically adjust signal parameters for different directions is limited
Solution Approach 1:
The patent achieves adaptability through parameter changes by dynamically adjusting signal amplitudes and polarities based on encoded direction information. The system uses bias gain factors that are applied to modify Lt and Rt signals differently depending on whether they represent front or rear directions, enabling versatile spatial audio reproduction without requiring a fundamentally complex decoder architecture.
Data Source
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AI summary
This audio matrix surround decoder requires minimal digital processing, useful in portable applications, particularly in playback from a portable player using a headphone or loudspeaker virtualizer. In one embodiment it pans inputs Lt and Rt to outputs associated with front directions in response to a measure of the sum of Lt and Rt being greater than a measure of the difference between Lt and Rt, and pans Lt and Rt to outputs associated with rear directions in response to a measure of the sum of Lt and Rt being less than a measure of the difference between Lt and Rt. Lt and Rt are modified to shift the direction of reproduced signals.