Frequency-Domain Audio Equalization to Prevent Gain Clipping
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Solution Overview
Problem
Graphic equalizers face challenges in preventing audio signal clipping and distortion when gains are set to high values, as the increased gains in adjacent bands interfere with each other, making it difficult to determine the appropriate gain limit and resulting in distorted sound waves.
Innovation Solution
An audio processor and processing method that includes a Fourier transform unit, filtering unit, inverse Fourier transform unit, band gain setting unit, volume setting unit, first filter coefficient calculator, and second filter coefficient calculator, which transform and filter audio signals in the frequency domain, calculate filter coefficients to adjust gains, and limit gains to prevent clipping by comparing them with an absolute volume gain, ensuring the signal remains within processable limits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If gains for respective bands are increased to maximize volume, then the volume level is improved, but the audio signal exceeds the full-scale value and clips causing distortion
Solution Approach 1:
The patent performs preliminary calculation of the maximum allowable gain for each frequency band by analyzing the audio signal characteristics before actual audio processing. This preliminary action determines the safe gain limits that prevent clipping while maximizing volume, resolving the contradiction between high volume and signal accuracy.
Solution Approach 2:
The patent dynamically adjusts the gain parameters for different frequency bands based on the calculated maximum allowable gains. By changing the gain parameters adaptively rather than using fixed high gains, the system maintains signal accuracy while achieving maximum volume without clipping.
2Power
If gains in adjacent bands are increased, then the overall gain is improved, but the adjacent gains interfere with each other making it difficult to determine the appropriate gain limit
Solution Approach 1:
The patent segments the frequency spectrum into discrete bands and calculates the maximum allowable gain for each band independently based on the audio signal characteristics in that band. This segmentation approach prevents interference between adjacent bands while determining appropriate gain limits, resolving the contradiction between overall gain and gain limit determination difficulty.
3Adaptability or versatility
If IIR filter is used to easily adjust gain in any frequency band, then the frequency characteristics adjustability is improved, but computational errors accumulate reducing accuracy
Solution Approach 1:
The patent introduces an intermediary calculation step that analyzes the audio signal characteristics and determines maximum allowable gains for each frequency band before applying the filter. This intermediary analysis acts as a mediator between the adjustable IIR filter and the final output, ensuring that gain adjustments maintain computational accuracy while preserving frequency characteristics adaptability.
4Measurement precision
If FIR filter is used to achieve high computational accuracy, then the computational accuracy is improved, but it is not easy to change only the gain in a particular frequency band
Solution Approach 1:
The patent dynamically adjusts the filter coefficients of the FIR filter based on the calculated maximum allowable gains for each frequency band. This dynamic adjustment allows the FIR filter to achieve both high computational accuracy and flexible frequency characteristics adaptability, resolving the contradiction between accuracy and adjustability.
Data Source
AI summary
An audio processor (1) includes a first filter coefficient calculator (31) that calculates a first filter coefficient so as to correspond to first gains for respective bands set by a user, a second filter coefficient calculator (32) that if values of third gains for respective bands of the first filter coefficient are greater than an absolute value of a second gain set by the user, calculates a second filter coefficient by limiting the values of the third gains for the respective bands to the amplitude value of the second gain, and a filtering unit (35) that filters an audio signal that has been transformed into a frequency-domain signal, using the second filter coefficient.