Audio Equalizer IIR Presets for Fixed-Point Overflow Control
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Solution Overview
Problem
High-order Infinite Impulse Response (IIR) filters used in Audio Equalizers (AEQ) experience nonlinear distortion due to overflow in fixed-point operations, leading to increased Total Harmonic Distortion (THD) when implemented on Digital Signal Processing (DSP) chips, particularly in High-Fidelity (HiFi) applications.
Innovation Solution
A method and apparatus for determining the preset of an AEQ by adjusting the frequency response-amplitude curves of second-order IIR filters to alleviate overflow issues, allowing for the adjustment of frequency response gains without changing the overall frequency response-amplitude curve of the AEQ, thereby reducing THD and improving performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a high-order IIR filter is implemented in fixed-point way on DSP chip, then the AEQ can be realized with limited hardware resources, but quantization errors of filter coefficients cause the practical frequency response to deviate from the desired theoretic design
Solution Approach 1:
The patent segments the high-order IIR filter into multiple second-order IIR filters connected in cascade. Each second-order filter has its own set of coefficients that can be independently optimized for fixed-point implementation. This segmentation reduces the cumulative quantization error compared to implementing a single high-order filter in fixed-point, while still achieving the desired overall frequency response characteristics.
2Reliability
If the frequency response-amplitude curves of second-order IIR filters are adjusted to alleviate overflow, then nonlinear distortion is reduced, but the individual filter gains change
Solution Approach 1:
The patent merges the individual frequency response-amplitude curves of multiple second-order IIR filters to achieve the desired overall frequency response. By adjusting individual filter curves and combining their effects through cascade connection, the system alleviates overflow issues in fixed-point operations while maintaining the target overall frequency response characteristics. The cumulative effect of multiple adjusted filters achieves both overflow prevention and accurate gain response.
3Ease of manufacture
If fixed-point operations are used in second-order IIR filters, then hardware implementation is feasible, but overflow occurs resulting in nonlinear distortion and increased THD
Solution Approach 1:
The patent changes the parameters (frequency response-amplitude curves) of the second-order IIR filters to prevent overflow in fixed-point operations. By carefully designing and adjusting these parameters, the system ensures that intermediate calculations remain within the representable range of fixed-point arithmetic, thereby eliminating nonlinear distortion and maintaining high audio quality while preserving hardware implementation feasibility.
Data Source
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AI summary
Disclosed are a determination method and apparatus for pre-set set parameters of an audio equalizer (AEQ), which are used for reducing an overflow phenomenon of fixed-point arithmetic output of all levels of second-order infinite impulse response (IIR) filters while frequency response amplitude curves of an AEQ remain unchanged, and reducing non-linear distortion, thus reducing total harmonic distortion (THD) of an AEQ system. The determination method for pre-set set parameters of an AEQ comprises: determining a first frequency point set by utilizing frequency response amplitude curves of an AEQ; adjusting the frequency response of frequency response amplitude curves of all levels of second-order IIR filters at a frequency point in the first frequency point set, so that the frequency response of the frequency response amplitude curves of all the levels of second-order IIR filters at the frequency point in the first frequency point set satisfies a pre-set condition; and adjusting a first parameter set and a second parameter set according to the adjusting variable of the frequency response amplitude curves of all the levels of second-order IIR filters, and determining the adjusted first parameter set and the adjusted second parameter set as pre-set set parameters of the AEQ.