AGCVariableAttackRelease

Overview

Peak follower with variable attack and release rates

Discussion

The AGCVariableAttackRelease module provides program-dependent peak following. This module has 2 attack time constants and 2 release time constants. When it is attacking, it will start by using the attackTimeInitial time constant. As the output level approaches the input level, it will smoothly vary to the attackTimeFinal time constant Likewise for release. This module also has an optional freeze pin. When the freeze pin is 1, then the state variable and the output values are frozen. When the freeze pin is deasserted, this module will continue operation from previous state.

Type Definition

CODE

typedef struct _ModuleAGCVariableAttackRelease
{
    ModuleInstanceDescriptor instance;            // Common Audio Weaver module instance structure
    FLOAT32 attackTimeInitial;                    // Envelope detector initial attack time constant
    FLOAT32 attackTimeFinal;                      // Envelope detector final attack time constant
    FLOAT32 releaseTimeInitial;                   // Envelope detector initial release time constant
    FLOAT32 releaseTimeFinal;                     // Envelope detector final release time constant
    FLOAT32 attackCoefInitial;                    // Computed coefficient used for initial attack
    FLOAT32 attackCoefFinal;                      // Computed coefficient used for final attack
    FLOAT32 releaseCoefInitial;                   // Computed coefficient used for initial release
    FLOAT32 releaseCoefFinal;                     // Computed coefficient used for final release
    INT32 attackMode;                             // Internal variable to keep track of the last mode (1 = attack, 0 = release, -1 = not started)
    FLOAT32 state;                                // Internal state variable. This is also the instantaneous output value.
    FLOAT32 startLevel;                           // Internal state variable to keep track of the initial value of the attack or release phase
} ModuleAGCVariableAttackReleaseClass;

Variables

Properties

Name	Type	Usage	isHidden	Default value	Range	Units
attackTimeInitial	float	parameter	0	0.01	0.001:100	msec
attackTimeFinal	float	parameter	0	0.01	0.001:100	msec
releaseTimeInitial	float	parameter	0	1	0.01:100	msec
releaseTimeFinal	float	parameter	0	50	0.01:1000	msec
attackCoefInitial	float	derived	1	0.8755	Unrestricted
attackCoefFinal	float	derived	1	0.8755	Unrestricted
releaseCoefInitial	float	derived	1	0.02062	Unrestricted
releaseCoefFinal	float	derived	1	0.0004166	Unrestricted
attackMode	int	state	1	-1	Unrestricted
state	float	state	1	0	Unrestricted
startLevel	float	state	1	0	Unrestricted

Pins

Input Pins

Name: in

Description: audio input

Data type: float

Channel range: Unrestricted

Block size range: Unrestricted

Sample rate range: Unrestricted

Complex support: Real

Name: freeze

Description: freezes the output and state variables

Data type: int

Channel range: 1

Block size range: Unrestricted

Sample rate range: Unrestricted

Complex support: Real

Output Pins

Name: out

Description: audio output

Data type: float

MATLAB Usage

File Name: agc_variable_attack_release_module.m

CODE

 M=agc_variable_attack_release_module(NAME, FREEZEPIN)
 Program dependent attack release envelope follower. The attack and 
 decay will smoothly vary between 2 user-specified values, depending
 on the amplitude characteristics of the signal being processed.
 Arguments:
    NAME - name of the module.
    FREEZEPIN - Optional boolean variable that specifies if the module has
    a freeze pin. By default, FREEZEPIN = 0.