Multiband Audio Compression Using Crossover Overshoot Feedback
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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 are not fully suppressed by stopband filters, leading to output signals exceeding desired limits.
Innovation Solution
A simple approach where the delayed output of a compressor is fed back to its gain path to suppress overshooting in subsequent samples, using an overshoot estimation module to generate an overshoot signal that adjusts the compressor's gain, thereby preventing overshooting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a multiband dynamic range compressor is used to compress specific frequency bands, then gain reduction is applied selectively to avoid reducing unrelated components, but overshooting occurs in crossover regions where adjacent bands overlap
Solution Approach 1:
The patent applies preliminary anti-action by estimating the overshoot amount before it occurs and applying compensatory gain reduction. The overshoot estimation module predicts the overshoot that will occur in crossover regions, and this estimation is fed back to adjust the compression threshold in advance, preventing the overshoot from exceeding the desired limit.
Solution Approach 2:
The patent implements feedback by taking the overshoot estimation output and feeding it back to the compression threshold adjustment mechanism. The estimated overshoot signal modifies the compression threshold dynamically, creating a closed-loop control system that continuously corrects for anticipated overshoot in crossover regions.
2Manufacturing precision
If sophisticated filter banks and frequency-domain processing are used to mitigate overshoot, then compression accuracy improves, but device complexity and cost increase
Solution Approach 1:
The patent substitutes complex mechanical/filter-based overshoot control with a computational approach. Instead of using sophisticated filter banks and frequency-domain processing, the invention uses a relatively simple overshoot estimation module that operates in the time domain, estimating overshoot based on the combined output signal and applying feedback control.
3Manufacturing precision
If the compression threshold is adjusted dynamically to prevent overshoot, then output signal accuracy improves, but processing time increases
Solution Approach 1:
The patent applies preliminary action by estimating the overshoot amount in advance and using this estimation to pre-adjust the compression threshold before the actual overshoot occurs. This proactive approach allows the system to prepare the correct threshold setting ahead of time, minimizing the need for reactive adjustments that would cause processing delays.
Data Source
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.