QMF Subband Filter Compression for Long HRTF Processing
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Solution Overview
Problem
The computational complexity of filtering in the Quadrature Mirror Filterbank (QMF) domain, particularly with long filters like head-related transfer functions (HRTF), is substantial due to the need to process numerous filter impulse responses, leading to high computational demands.
Innovation Solution
A filter compressor is introduced that selects and constructs compressed subband filter impulse responses by identifying and retaining only the higher-value filter impulse responses, setting lower-value ones to zero, thereby reducing the number of coefficients and simplifying the filtering process in the QMF domain.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If long HRTF filters are used to model room characteristics, then audio quality is improved, but computational complexity increases significantly
Solution Approach 1:
The patent segments the long HRTF filter into multiple shorter subband filters in the QMF domain. Each subband filter processes a specific frequency range, allowing the overall filtering function to be distributed across multiple simpler operations rather than one complex long filter
Solution Approach 2:
The patent extracts and removes insignificant filter coefficients from the subband filters based on threshold criteria. By identifying and eliminating coefficients with minimal impact on audio quality, the filter length is reduced while maintaining essential filtering functionality
2Reliability
If all filter impulse response values are processed, then filtering accuracy is maintained, but computational demands increase
Solution Approach 1:
The patent applies different processing strategies to different portions of the filter impulse response based on local characteristics. Significant coefficients are retained with full precision while insignificant coefficients are removed or quantized, creating non-uniform processing that adapts to local signal properties
Solution Approach 2:
The patent processes only the necessary portion of filter coefficients rather than all coefficients equally. By applying threshold-based selection, only coefficients above a certain significance level are fully processed, while others are simplified or discarded
Data Source
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AI summary
A filter system comprises a filter converter (101) and a filter compressor (102) for generating compressed subband filter impulse responses from input subband filter impulse responses corresponding to subbands, which comprise filter impulse response values at filter taps. The filter compressor comprises a processor (820) for examining the filter impulse response values from at least two input subband filter input responses to find filter impulse response values having higher values and at least one filter impulse response value having a value being lower than the higher values, and a filter impulse response constructor (305) for constructing the compressed subband filter impulse responses using the filter impulse response values having the higher values, wherein the compressed subband filter impulse responses do not include filter impulse response values corresponding to filter taps of the at least one filter impulse response value having the lower value or comprise zero-valued values corresponding to filter taps of the at least one filter impulse response value having the lower value.