Audio Filterbank Impulse Response Shaping for Low-Latency Resolution
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Solution Overview
Problem
Existing audio filter banks face latency issues due to the need for lower frequency filters to use a defined number of samples to accurately represent their impulse response, which constrains the overall latency of the filter bank.
Innovation Solution
The method involves generating modified impulse responses by performing fade and time reverse operations on ideal impulse responses, allowing for reduced latency while preserving the impulse response of the filter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If lower frequency filters use a defined number of samples to accurately represent the impulse response, then the frequency resolution is improved, but the latency increases
Solution Approach 1:
The impulse response is segmented into multiple sections (first section and second section) with different characteristics. The first section contains the initial samples with full precision, while the second section uses fewer samples or approximations. This segmentation allows the filter to achieve accurate frequency resolution in the critical initial period while reducing overall latency by not requiring a full-length impulse response for all frequency bands.
Solution Approach 2:
Different sections of the impulse response are assigned different qualities or precision levels. The first section (earlier time samples) maintains high precision to ensure accurate frequency representation, while the second section (later time samples) uses reduced precision or fewer samples. This local differentiation resolves the contradiction by applying high precision only where it is most critical for frequency resolution while reducing latency through the truncated second section.
2Loss of time
If high frequency filters use fewer samples, then the latency is reduced, but the frequency resolution deteriorates
Solution Approach 1:
The patent applies different sample lengths and precision levels to different frequency bands and time sections. High frequency filters use fewer samples in the second section compared to low frequency filters, reducing their latency. Meanwhile, the first section maintains sufficient samples across all frequency bands to preserve frequency resolution where it matters most. This localized quality adjustment resolves the contradiction between latency and frequency resolution for high frequency filters.
Solution Approach 2:
The filter bank dynamically adjusts the number of samples used for different frequency bands and time sections. Rather than using a fixed uniform sample length for all filters, the system adapts the impulse response length based on frequency content and temporal requirements, allowing high frequency filters to operate with shorter effective lengths (reduced latency) while maintaining frequency resolution through adaptive weighting and combination of sections.
3Loss of time
If the impulse response is truncated to reduce latency, then the latency is reduced, but the filter response accuracy deteriorates
Solution Approach 1:
The impulse response is divided into a first section (retained in full) and a second section (truncated or approximated). This segmentation allows the system to reduce latency by truncating the second section while preserving filter response accuracy through the complete first section, which contains the most critical information for accurate filtering. The weighted combination of these sections maintains reliability while achieving lower latency.
Solution Approach 2:
Rather than using the complete impulse response (excessive action), the patent applies partial action by using only the necessary portion (first section) in full detail and a reduced portion (second section) for the remaining requirements. This partial approach achieves the minimum necessary latency reduction while maintaining sufficient filter response accuracy through the preserved first section and appropriate weighting schemes.
Data Source
AI summary
A filterbank, suitable for modifying audio signals with dynamic gains in each band, is constructed so that the perceived latency is small, while a larger group delay is applied at low frequencies to enable higher frequency resolution in the lower frequency bands. The higher group delay at low frequencies is achieved by inserting an all-pass filter into the reconstructed filter response.