Adaptive Feedback Limiter Control for Audio Pumping and Overshoot
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Solution Overview
Problem
Existing audio signal compression and limiting technologies face challenges such as 'volume pumping', harmonic distortion, and overshooting due to fixed or adaptive control characteristics that do not account for varying dynamic changes across different frequency ranges, leading to suboptimal signal amplification and distortion in audio systems.
Innovation Solution
A method using a compressor with a feedback network that operates in two modes: attack and release, where the gain control characteristic is adaptive or fixed based on signal levels, allowing for dynamic adjustment of attack and release times to minimize artifacts like volume pumping and distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a fixed control characteristic is used in compressors and limiters, then the circuit structure is simple and easy to implement, but volume pumping effects and harmonic distortion occur due to inability to adapt to varying dynamic changes in different frequency ranges
Solution Approach 1:
The patent applies dynamics by making the control characteristic adaptive rather than fixed. The compressor/limiter automatically adjusts its control characteristics based on the detected signal level and dynamic changes, allowing the system to adapt to varying conditions in different frequency ranges and eliminate volume pumping effects and harmonic distortion.
Solution Approach 2:
The patent changes the control parameters dynamically based on signal characteristics. By detecting signal level and dynamic changes, the system adjusts control parameters such as attack and release times adaptively, transforming the fixed parameter system into a variable parameter system that responds to different frequency ranges and signal conditions.
2Object-generated harmful factors
If an adaptive control characteristic is used throughout the entire dynamic range, then volume pumping effects are reduced, but the system becomes overly sensitive to small signal level changes causing excessive gain adjustment
Solution Approach 1:
The patent applies local quality by implementing different control characteristics for different signal level ranges. Instead of using a single adaptive control characteristic for the entire dynamic range, the system uses multiple control characteristics that are selectively applied based on the local signal conditions, with each characteristic optimized for specific signal level ranges to prevent excessive gain adjustment.
Solution Approach 2:
The patent applies partial action by using adaptive control only when and where it is needed, rather than continuously across all signal levels. The system selectively engages adaptive control characteristics based on detected signal conditions, applying adaptation partially to avoid excessive sensitivity to small changes while still reducing volume pumping effects in critical ranges.
3Speed
If the attack time is made very short to respond quickly to signal changes, then the limiter responds faster to prevent distortion, but overshooting occurs in the output signal
Solution Approach 1:
The patent applies preliminary action by detecting signal level and dynamic changes in advance before the actual limiting action occurs. The system uses a detection stage that monitors incoming signals and prepares appropriate control characteristics, allowing the limiter to respond proactively to upcoming signal peaks and prevent overshooting before it occurs.
Solution Approach 2:
The patent applies dynamics by making the attack time variable rather than fixed. The system adjusts attack time dynamically based on signal characteristics, using shorter attack times when needed for fast response while automatically extending attack time when signal conditions indicate risk of overshooting, thereby achieving both fast response and overshooting prevention.
Data Source
AI summary
The invention relates to a compressor and method for amplifying an input signal with a controlled gain. An output signal representing the input signal is amplified by an initial gain and a signal level of the input signal or of the output signal is compared with a threshold level. If the signal level is below the threshold level, the initial gain value is updated using an adaptive control characteristic, and if the signal level is above the threshold level, the initial gain value is updated using a fixed control characteristic or an adaptive control characteristic respectively. The adaptive control characteristic is dependent on the signal level and the fixed control characteristic is independent from the signal level.