Overview
Soft knee gain computer for use in peak limiters
Discussion
The limiter core provides a peak amplitude follower and input/output gain transfer function for use in AGC systems. It is designed to take as its input the output of the BlockStatistics or the Abs module. The module outputs the time varying gain on the output pin which is typically used as input to the AGCMultiplier or a ScalerNControl module
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V2 was introduced to allow multichannel inputs which in effect significantly reduces the module processing load compared to using multiple instances of the initial single channel version.
Type Definition
Code Block |
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typedef struct _ModuleAGCLimiterCoreV2 { ModuleInstanceDescriptor instance; // Common Audio Weaver module instance structure INT32 numChan; // Number of channels. FLOAT32* threshold; // Amplitude level at which the AGC Limiter Core reduces its output gain value FLOAT32* gain; // Value used to scale the output of the AGC Limiter Core (make up gain) FLOAT32* kneeDepth; // Knee depth controls the sharpness of the transition between no limiting and limiting FLOAT32* ratio; // Slope of the output attenuation when the signal is above threshold - derived from the standard compression ratio parameter by the formula slope = 1.0 - (1.0/ratio) FLOAT32* attackTime; // Envelope detector attack time constant FLOAT32* decayTime; // Envelope detector decay time constant FLOAT32* slope; // Internal derived variable which holds the slope of the compression curve FLOAT32* sharpnessFactor; // Internal derived variable which is used to implement the soft knee FLOAT32* attackCoeff; // Internal derived variable which implements the attackTime FLOAT32* decayCoeff; // Internal derived variable which implements the decayTime FLOAT32* envState; // Holds the instantaneous state of the envelope detector FLOAT32* currentGain; // Instantaneous gain computed by the block } ModuleAGCLimiterCoreV2Class; |
Variables
Properties
Name | Type | Usage | isHidden | Default value | Range | Units |
numChan | int | const | 1 | 1 | Unrestricted | |
threshold | float* | parameter | 0 | [1 x 1] | -60:0 | dB |
gain | float* | parameter | 0 | [1 x 1] | 0:60 | dB |
kneeDepth | float* | parameter | 0 | [1 x 1] | 0.1:60 | dB |
ratio | float* | parameter | 0 | [1 x 1] | 1:100 | |
attackTime | float* | parameter | 0 | [1 x 1] | 1:2000 | msec |
decayTime | float* | parameter | 0 | [1 x 1] | 1:2000 | msec |
slope | float* | derived | 1 | [1 x 1] | Unrestricted | dB/dB |
sharpnessFactor | float* | derived | 1 | [1 x 1] | Unrestricted | |
attackCoeff | float* | derived | 1 | [1 x 1] | Unrestricted | |
decayCoeff | float* | derived | 1 | [1 x 1] | Unrestricted | |
envState | float* | state | 1 | [1 x 1] | Unrestricted | |
currentGain | float* | state | 0 | [1 x 1] | Unrestricted |
Pins
Input Pins
Name: in
Description: audio input
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Sample rate range: Unrestricted
Complex support: Real
Output Pins
Name: out
Description: audio output
Data type: float
Scratch Pins
Channel count: 1
Block size: 32
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Block size: 32
Sample rate: 48000
MATLAB Usage
File Name: agc_limiter_core_v2_module.m
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