Frequency-Warped Audio Equalizer for Accurate Low-Cost Filtering
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Solution Overview
Problem
Audio equalizers face a tradeoff between computing resource usage and accuracy, with IIR filters being resource-efficient but inaccurate, and FIR filters being accurate but resource-intensive, especially in mobile devices where adjusting one frequency band affects adjacent bands, leading to poor accuracy.
Innovation Solution
The development of frequency-warped audio equalization filters that transform initial filters to reduce computing resource usage while maintaining or improving accuracy, using techniques like frequency warping and all-pass filters to minimize effects on adjacent frequency bands.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If IIR filters are used for audio equalization, then computing resource usage is reduced, but accuracy deteriorates because adjusting one frequency band affects adjacent bands
Solution Approach 1:
The audio spectrum is divided into multiple frequency bands, each processed by a separate filter section. This segmentation isolates the effect of adjustments in one band from adjacent bands, improving frequency response accuracy while maintaining computational efficiency through the use of efficient filter structures within each band.
Solution Approach 2:
The patent transforms the filter parameters through frequency warping techniques, mapping standard frequency bands to perceptually relevant bands. This parameter transformation allows the filter to achieve accurate frequency response control in perceptually important regions while using computationally efficient IIR filter structures.
2Measurement precision
If FIR filters are used for audio equalization, then accuracy is improved, but computing resource usage increases
Solution Approach 1:
The patent applies frequency warping parameter transformations to IIR filter structures, enabling them to achieve frequency response characteristics comparable to FIR filters. By transforming the s-plane to z-plane using bilinear transformation and applying pre-warping, the IIR filters achieve accurate control over frequency bands with much lower computational requirements than equivalent FIR filters.
Solution Approach 2:
The patent replaces the computationally intensive FIR filter mechanism with a more efficient IIR filter mechanism that uses feedback loops and recursive calculations. This substitution maintains frequency response accuracy through careful pole-zero placement and frequency warping while significantly reducing the number of multiply-accumulate operations required per sample.
3Ease of operation
If frequency bands are adjusted in traditional equalizers, then gain control is achieved, but accuracy deteriorates because adjacent bands are affected
Solution Approach 1:
The equalizer divides the frequency spectrum into distinct, non-overlapping bands with dedicated control sections. Each band's gain adjustment is isolated through bandpass filtering and selective amplification, allowing users to control individual frequency regions without affecting adjacent bands, thereby maintaining both ease of operation and frequency response accuracy.
Solution Approach 2:
The patent introduces intermediate processing stages including bandpass filters, gain control sections, and frequency warping transformations between the user interface and the final output. These intermediary elements decouple the user's simple gain adjustment actions from the complex frequency domain interactions, enabling easy operation while preserving spectral accuracy.
Data Source
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AI summary
In certain embodiments, an improved audio equalization filter can be generated by frequency warping one or more digital filters having a plurality of frequency bands. Frequency warping can include, for example, transforming at least some of the frequency bands of the one or more digital filters into lower frequency bands. As a result, in various implementations the audio equalization filter may be more accurate than certain currently-available IIR equalization filters. The audio equalization filter may also be more computing-resource efficient than certain currently-available FIR equalization filters.