Hybrid GPEQ Filter Tuning for Asymmetric Transaural Audio
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Solution Overview
Problem
Current transaural audio systems face challenges in preserving the relative phase of audio signals due to the use of 2nd order IIR filter sections, leading to loss of spatial audio quality and increased crosstalk in asymmetric speaker configurations, particularly in low-cost mobile devices.
Innovation Solution
A Gain Phase Equalization (GPEQ) filter is introduced, comprising an asymmetric FIR filter bank and an IIR filter bank, which normalizes magnitude and group delay responses, and corrects residual asymmetry while preserving relative phases, using a hybrid filter architecture that is modular, inexpensive, and easy to tune.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If 2nd order IIR filter sections are used for asymmetric PEQ, then magnitude asymmetry can be corrected, but relative phase is lost and crosstalk increases
Solution Approach 1:
The filter is segmented into two distinct parts: an asymmetric FIR filter bank for magnitude correction and a symmetric IIR filter bank for phase preservation. This segmentation allows each part to specialize in its strength while compensating for the other's weaknesses.
Solution Approach 2:
The patent creates a composite filter system combining FIR and IIR filter banks. The FIR section handles magnitude asymmetry with linear phase characteristics, while the IIR section preserves relative phase with its minimal phase characteristics, creating a composite solution that leverages both filter types' advantages.
2Manufacturing precision
If asymmetric PEQ is applied to compensate for speaker asymmetry, then magnitude response is improved, but group delay and phase response asymmetry worsens
Solution Approach 1:
The patent applies local quality by making the FIR filter bank asymmetric to match the local characteristics of each speaker's magnitude response, while keeping the IIR filter bank symmetric to maintain global phase coherence across both channels.
3Reliability
If standard CTC filters are used, then crosstalk cancellation is achieved, but they assume symmetric reproduction and cannot handle asymmetric magnitude response
Solution Approach 1:
The GPEQ filter bank performs preliminary action by pre-correcting magnitude and phase asymmetries before the CTC filter processes the signal. This preparation ensures that the CTC filter receives pre-conditioned signals that account for asymmetric speaker characteristics, enabling effective crosstalk cancellation in asymmetric configurations.
Data Source
Figure 1a~1c
Figure 2
Figure 3a
AI summary
A GPEQ filter and tuning methods for asymmetric transaural audio reproduction on mobile consumer devices. The GPEQ filter includes an asymmetric FIR filter bank configured to normalize the magnitude responses of at least two audio speakers to a target response above a low frequency cross-over of the audio speakers as reproduced at the listener position and a symmetric MR filter bank component configured to high pass filter above the low frequency cross-over and equalize the magnitude responses of the at least two audio speakers. In some embodiments the FIR filter bank is configured to normalize the group delay of the audio channels and in some embodiments the MR filter bank includes an asymmetric IIR filter bank component configured to correct any residual asymmetry in the magnitude responses of the at least two audio speakers. Phase preservation may be accomplished using phase-balanced or phase- compensated IIR filter sections.