ExpanderCore

Overview

Upward and Downward Expander module with programmable attack and release time constants

Discussion

Envelope detector used in dynamics processor. The module accepts a mono channel buffer of amplitude and produces an output buffer the same size as the input. An envelope detector is applied to the input that has programmable attack and release times. The attack time applies when the current input value is larger than the state of the envelope detector. Similarly, the release time applies when the current input value is smaller than the state of the envelope detector. The expander increases or decreases the output gain based on the value and sign of ratio when the input energy level is below the threshold.

Type Definition

CODE

typedef struct _ModuleExpanderCore
{
    ModuleInstanceDescriptor instance;            // Common Audio Weaver module instance structure
    INT32 plot;                                   // When true, plots Gain and Static curves.
    FLOAT32 attackTime;                           // Speed at which the expander reacts to increasing levels.
    FLOAT32 releaseTime;                          // Speed at which the expander reacts to decreasing levels.
    FLOAT32 threshold;                            // Input energy level at which the expander changes outpupt gain.
    FLOAT32 ratio;                                // ratio of output energy to input energy, a negative value indicates an upward expander.
    FLOAT32 kneeDepth;                            // Specifies the curvature of the smooth region connecting the two line segments
    FLOAT32 maxGain;                              // maximun output gain
    FLOAT32 minGain;                              // minimun output gain
    FLOAT32 slope;                                // left slope of gain curve.
    FLOAT32 attackCoeff;                          // Internal coefficient realizing the attack time.
    FLOAT32 releaseCoeff;                         // Internal coefficient realizing the release time.
    FLOAT32 envState;                             // Previous state of evelope detector
    FLOAT32* kneePoly;                            // Derived variable for interpolating the soft knee for Gain Curve
    FLOAT32* kneePolyS;                           // Derived variable for interpolating the soft knee for Static Curve
} ModuleExpanderCoreClass;

Variables

Properties

Name	Type	Usage	isHidden	Default value	Range	Units
plot	int	parameter	0	0	0:1:1
attackTime	float	parameter	0	2	0.01:1:1000	msec
releaseTime	float	parameter	0	100	0.01:1:1000	msec
threshold	float	parameter	0	-20	-100:0.1:100	dB
ratio	float	parameter	0	0.2	-1:0.01:1	dB/dB
kneeDepth	float	parameter	0	3	0:0.1:20
maxGain	float	parameter	0	20	0:0.1:100	dB
minGain	float	parameter	0	-20	-100:0.1:0	dB
slope	float	derived	1	4	Unrestricted
attackCoeff	float	derived	1	0.01036	Unrestricted
releaseCoeff	float	derived	1	0.0002083	Unrestricted
envState	float	derived	1	0	Unrestricted
kneePoly	float*	derived	1	[1 x 3]	Unrestricted
kneePolyS	float*	derived	1	[1 x 3]	Unrestricted

Pins

Input Pins

Name: in

Description: audio input

Data type: float

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: expander_core_module.m

CODE

 M=expander_core_module(NAME)
 Upward and Downward Expander module with programmable attack and release time constants.
 
 Arguments:
    NAME - name of the module.
 Author:  Darrel Judd