Multiband Audio Compression with Feedback Overshoot Suppression
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Solution Overview
Problem
Conventional multiband dynamic range compressors often experience overshooting issues due to input audio signal energy in the crossover or overlapping regions of frequency bands, which is not fully suppressed, leading to output signals exceeding the desired limit, particularly in real-time applications where sophisticated filter banks and frequency-domain processing are not suitable for low-cost microcontrollers or digital signal processors.
Innovation Solution
A simple approach is implemented where the delayed output of a compressor is fed back to the input of the same compressor's gain path to suppress overshooting in subsequent samples, using an overshoot estimation module to calculate and adjust the gain accordingly, thereby preventing overshooting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a multiband dynamic range compressor is used to compress only specific frequency bands, then the desired frequency-selective compression effect is achieved, but overshooting occurs in the crossover regions where adjacent bands overlap
Solution Approach 1:
The patent applies preliminary action by estimating the overshoot amount before the recombination of compressed and uncompressed bands, and pre-adjusting the compression gain accordingly. The overshoot estimation module calculates the expected overshoot in crossover regions based on the uncompressed band signal, and this estimation is used to modify the compression behavior in advance, preventing the overshoot from occurring in the final output.
2Manufacturing precision
If sophisticated filter banks and frequency-domain processing are used to mitigate overshooting, then overshoot suppression performance is improved, but device complexity and computational cost increase
Solution Approach 1:
The patent replaces complex mechanical/filter-based overshoot suppression systems with a computational approach. Instead of using sophisticated filter banks and frequency-domain processing, the invention uses a straightforward time-domain overshoot estimation and gain adjustment mechanism. The overshoot estimation module uses simple signal processing to estimate overshoot based on the uncompressed band signal, and the gain adjustment is applied directly in the time domain, avoiding the need for complex frequency-domain transformations.
3Measurement precision
If the compression threshold is strictly enforced at the center frequency, then the target compression level is achieved, but frequencies near the crossover regions exceed the desired limit
Solution Approach 1:
The patent applies preliminary anti-action by estimating the overshoot that will occur in crossover regions and applying a counteracting gain reduction in advance. The overshoot estimation module predicts the amount of overshoot that will occur when compressed and uncompressed bands are recombined, and the compression gain is adjusted accordingly before recombination, effectively canceling out the harmful overshoot effect.
Data Source
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AI summary
Provided is an audio-signal dynamic-range-compression system. An input line accepts an input signal. A filter set coupled to the input line divides the input signal into a set of frequency bands, including a first frequency band and a second frequency band. A compressor has a first input that receives the first frequency band, a second input and an output. An adder has a first input coupled to the output of the compressor, a second input coupled to the second frequency band, and an output. An overshoot estimation module has an input coupled to the output of the adder and an output coupled to the second input of the compressor. The output of the overshoot estimation module provides an overshoot signal that indicates a result of a comparison between a signal at the input of the overshoot estimation module and a specified threshold.