Audio Dynamics Control With Exponential Release to Cut Ripple
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Solution Overview
Problem
Existing audio dynamics processors face challenges with audible modulation and distortion due to fixed release time constants, which can lead to 'dead zones' and excessive ripple in control signals, particularly when dealing with high-gain guitar systems and composite music.
Innovation Solution
A circuit and process that generates a control signal with an exponential release response, using logarithmic detection and filtering to reduce ripple and introduce a dead band, converting the signal into a release current for dynamic audio processing, and optionally providing an exponential attack response.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a fast time constant is used for the control voltage, then the release response is fast and responsive, but excessive ripple in the control signal causes audible distortion and pumping effects
Solution Approach 1:
The patent implements dynamic time constant control where the release time constant automatically adjusts based on the control voltage level. When the control voltage is high (signal above threshold), a fast time constant provides rapid response. When the control voltage drops below threshold, the time constant automatically increases to filter ripple and prevent pumping effects. This dynamic adjustment resolves the contradiction between fast response and ripple suppression.
2Object-generated harmful factors
If a slow release time constant is used, then audible distortion and pumping effects are reduced, but the noise floor becomes audible when the input signal stops suddenly
Solution Approach 1:
The system dynamically switches between fast and slow time constants based on signal level. During active signaling, the fast time constant ensures rapid follow-up. When the signal drops below threshold, the slow time constant takes over to prevent noise floor audibility while still providing adequate ripple filtering. This resolves the contradiction between preventing distortion and avoiding noise floor exposure.
3Device complexity
If a fixed release time constant is used, then the circuit is simple to implement, but it creates dead zones and cannot adapt to different signal conditions
Solution Approach 1:
The patent implements a dynamic time constant circuit that automatically adjusts the release time constant based on the control voltage level and signal conditions. The circuit monitors the control voltage and switches between different time constant values, providing fast response above threshold and slow response below threshold. This adds adaptability while maintaining reasonable circuit complexity through automated control.
4Force
If the timing capacitor charges well in excess of the threshold point, then the expander provides adequate headroom, but a dead zone is created where the control signal decreases but has no effect on the downward expander
Solution Approach 1:
The dynamic time constant circuit resolves the dead zone issue by automatically adjusting the time constant based on signal level. When the control voltage is high (charging phase), the fast time constant ensures rapid response without excessive headroom. When the voltage drops below threshold, the slow time constant takes over, eliminating the dead zone by providing continuous control action. This ensures both adequate headroom and continuous responsiveness.
Data Source
AI summary
An input audio signal is detected to provide a fast time constant control signal which is clamped for immediate response when the input signal drops below a threshold level and filtered to provide a modified control signal with a slow time constant. As the modified control signal level decreases toward the control signal level, a time constant differential control signal decreases and slows the rate of change of the decreasing modified control signal which, as it nears the control signal level, reverts to a slow response. The resulting control signal has an exponential release response which can be applied to an audio dynamics processor. The time constant differential control signal may also be detected to provide an inverted output when it is significantly less than the modified control signal so as to result in the control signal also having an exponential attack response to be applied to the processor.