Overview

Gain computer for use in Compressor

Discussion

This module takes as input the max absolute value of the inputs, computes an envelope follower (with settable attack and decay rates), and computes the appropriate gain based on threshold, gain, and slope parameters. The output has a linear gain factor. The computation is performed once per tick.

The envelope follower uses the maximum value of the input within the tick for its calculation. The output gain is smoothed with a one-pole smoother to reduce zipper noise.

Type Definition

typedef struct _ModuleAGCCompressorCoreFract32
{
    ModuleInstanceDescriptor instance;            // Common Audio Weaver module instance structure
    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.
    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 attackTimeMin;                        // Minimum value of the attack time constant.
    FLOAT32 decayTime;                            // Envelope detector decay time constant.
    FLOAT32 decayTimeMin;                         // Minimum value of the decay time constant.
    fract32 currentGain;                          // Instanteous gain applied at the end of the block.
    fract32 thresholdFract32;                     // threshold - in 8.24 "base2 dB"
    fract32 gainFract32;                          // outputGain - in 8.24 "base2 dB"
    fract32 slope;                                // Internal parameter which holds the slope of the compression curve.
    FLOAT32 sharpnessFactor;                      // Unused variable. Kept in for legacy support
    fract32 attackCoeff;                          // Internal derived coefficient based on the attackTime
    fract32 attackCoeffSmoothing;                 // Internal derived coefficient based on the attackTimeMin
    fract32 decayCoeff;                           // Internal derived coefficient based on decayTime
    fract32 decayCoeffSmoothing;                  // Internal derived coefficient based on decayTimeMin
    fract32 envState;                             // State of the envelope detector one-pole filter - runs at tick rate.
} ModuleAGCCompressorCoreFract32Class;

Variables

Properties

Name	Type	Usage	isHidden	Default value	Range	Units
threshold	float	parameter	0	-30	-60:0	dB
gain	float	parameter	0	10	0:100	dB
ratio	float	parameter	0	4	1:100
attackTime	float	parameter	0	20	20:100	msec
attackTimeMin	float	parameter	0	20	Unrestricted
decayTime	float	parameter	0	100	20:1000	msec
decayTimeMin	float	parameter	0	20	Unrestricted
currentGain	fract32	state	0	0	Unrestricted
thresholdFract32	fract32	derived	0	-0.2344	Unrestricted
gainFract32	fract32	derived	0	0.07813	Unrestricted
slope	fract32	derived	1	0.005859	0:100	dB/dB
sharpnessFactor	float	derived	1	0	Unrestricted
attackCoeff	fract32	derived	1	1	Unrestricted
attackCoeffSmoothing	fract32	derived	1	0.001041	Unrestricted
decayCoeff	fract32	derived	1	0.01324	Unrestricted
decayCoeffSmoothing	fract32	derived	1	0.0004166	Unrestricted
envState	fract32	state	1	0	Unrestricted

Pins

Input Pins

Name: in

Description: audio input

Data type: fract32

Channel range: 1

Block size range: Unrestricted

Sample rate range: Unrestricted

Complex support: Real

Output Pins

Name: out

Description: audio output