Adaptive Feedback Limiter for Fast Attack and Smooth Release
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Solution Overview
Problem
Existing audio compressors and limiters face challenges in managing dynamic changes across different frequency ranges, leading to issues like volume pumping, harmonic distortion, and overshooting, which affect the quality of audio signals, especially in noisy environments like vehicles where power supply is limited.
Innovation Solution
A method and circuit design that employs a controlled amplifier with a feedback network operating in two modes - attack and release modes - using either adaptive or fixed control characteristics based on signal levels, allowing for dynamic gain adjustment to reduce the dynamic range of audio signals while minimizing unwanted artifacts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a compressor or limiter is used to reduce dynamic range, then the maximum input levels are limited and system damage is prevented, but volume pumping and harmonic distortion occur
Solution Approach 1:
The patent implements dynamic adaptation of the release time constant based on the signal level. When the signal level is high, a shorter release time constant is used to quickly reduce gain and prevent distortion. When the signal level is low, a longer release time constant is used to smoothly restore gain and avoid volume pumping effects. This dynamic adjustment resolves the contradiction between protecting the system and avoiding harmful artifacts.
Solution Approach 2:
The patent changes the release time constant parameter adaptively based on the signal level. By switching between different time constant values depending on whether the signal is above or below a threshold, the system achieves both protection against overload and minimization of distortion artifacts, resolving the technical contradiction.
2Speed
If the release time constant is shortened to respond quickly to signal changes, then the response speed is improved, but volume pumping effects increase
Solution Approach 1:
The patent makes the release time constant dynamic rather than fixed. During high signal levels (attack mode), a short time constant provides fast response. During low signal levels (release mode), a long time constant prevents volume pumping. This dynamic behavior resolves the contradiction between response speed and avoiding harmful effects.
3Object-generated harmful factors
If the release time constant is lengthened to reduce volume pumping, then volume pumping effects are minimized, but the response to high signal levels becomes slower
Solution Approach 1:
The patent implements a dual-mode system where the release time constant is adaptively selected based on signal level. In attack mode (high signal), a short time constant ensures fast response. In release mode (low signal), a long time constant minimizes volume pumping. This resolves the contradiction by applying different time constants in different operational contexts.
4Adaptability or versatility
If different dynamic changes occur in different frequency ranges simultaneously, then the audio signal complexity is preserved, but non-ideal compressor behavior and distortion increase
Solution Approach 1:
The patent uses a feedback mechanism that continuously monitors the output signal level and adjusts the gain accordingly. The feedback loop compares the actual output level with the desired level and modifies the compression parameters in real-time, enabling the compressor to handle complex multi-frequency signals while maintaining ideal behavior and minimizing distortion.
Data Source
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AI summary
The invention relates to a compressor and method for amplifying an input signal with a controlled gain comprising the steps of: providing an output signal representing the input signal amplified by an initial gain; determining a signal level of the input signal or of the output signal; comparing the signal level with a threshold level; if the signal level is below the threshold level, updating the initial gain value using an adaptive control characteristic; and if the signal level is above the threshold level, updating, dependent on the signal level, the initial gain value using a fixed control characteristic or an adaptive control characteristic respectively; the adaptive control characteristic being dependent on the signal level and the fixed control characteristic being independent from the signal level.