Audio Equalizer Preset for Fixed-Point IIR Overflow Control
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Solution Overview
Problem
In Audio Equalizers (AEQ) implemented on Digital Signal Processing (DSP) chips, fixed-point operations can lead to overflow issues in second-order IIR filters, resulting in nonlinear distortion and increased Total Harmonic Distortion (THD), particularly in High-Fidelity applications.
Innovation Solution
A method and apparatus for determining the preset of an Audio Equalizer that adjusts frequency response gains of second-order IIR filters to prevent overflows, by determining a set of frequencies where amplitudes are below a threshold, and adjusting parameters to ensure the sum of adjusted frequency response-amplitude curves meet specific conditions without altering the overall frequency response curve.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If fixed-point operations are used in second-order IIR filters, then computational efficiency is improved, but overflow occurs resulting in nonlinear distortion and increased THD
Solution Approach 1:
The patent applies preliminary action by pre-calculating the frequency response-amplitude curves of all second-order IIR filters and identifying frequencies where overflow may occur before actual audio processing. The system determines a first set of frequencies where the frequency response-amplitudes are below or equal to a first pre-defined threshold, and pre-adjusts the frequency response-amplitude curves at these frequencies to prevent overflow during fixed-point operations.
Solution Approach 2:
The patent applies parameter changes by adjusting the frequency response-amplitude curves of the second-order IIR filters at specific frequencies. The system modifies the amplitude parameters at the first set of frequencies while maintaining the overall frequency response curve, thereby changing local parameter values to prevent overflow without altering the global filter characteristics.
2Reliability
If frequency response gains are adjusted to prevent overflow, then nonlinear distortion is reduced, but the complexity of determining adjusted parameters increases
Solution Approach 1:
The patent applies self-service by implementing an automated algorithm that independently determines the first set of frequencies, calculates adjustment amounts, and modifies the frequency response-amplitude curves without requiring manual intervention. The system automatically ensures that the sum of adjusted frequency response-amplitude curves meets pre-defined conditions while maintaining the overall frequency response curve.
Solution Approach 2:
The patent applies feedback by using the determined frequency response-amplitude curves as feedback to identify frequencies requiring adjustment. The system monitors the amplitude levels at different frequencies and uses this information to adjust the parameters of second-order IIR filters, creating a closed-loop process that ensures overflow prevention while maintaining signal fidelity.
3Reliability
If the frequency response-amplitude curves of second-order IIR filters are adjusted, then overflow is prevented, but the overall frequency response curve must remain unchanged
Solution Approach 1:
The patent applies local quality by making adjustments only at specific frequencies (the first set of frequencies) where overflow risk exists, rather than uniformly adjusting all frequency points. The system modifies the frequency response-amplitude curves locally at these critical frequencies while leaving other frequencies unchanged, thereby preventing overflow without distorting the overall frequency response characteristics.
Solution Approach 2:
The patent applies partial action by adjusting only the necessary portion of the frequency response-amplitude curves - specifically at frequencies where the amplitude is below or equal to the first pre-defined threshold. This selective adjustment prevents overflow at critical points while minimizing changes to the overall frequency response, thereby maintaining manufacturing precision.
Data Source
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.