Overview

Subband envelope detector array with programmable attack and release times

Discussion

Envelope detector array used in dynamics processor. The module accepts an N-sample buffer of amplitude and produces an output buffer the same size as the input. A separate envelope detector with programmable attack and release times is applied to each sample of the input. Subsequent samples for each detector are taken from the corresponding sample of subsequent blocks. 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. After a detector reaches its maximum value, the peak is held for holdTime msec. Only after the holdTime has elapsed does the detector start decaying. If a larger value arrives while the output is being held, the larger value overrides the holding operation, the detector attacks, and the output is held again for the specified holdTime.

Type Definition

typedef struct _ModuleSbAttackRelease
{
    ModuleInstanceDescriptor instance;            // Common Audio Weaver module instance structure
    FLOAT32 attackTime;                           // Speed at which the detector reacts to increasing levels.
    FLOAT32 holdTime;                             // Duration to hold the output constant after the peak has been reached.
    FLOAT32 releaseTime;                          // Speed at which the detector reacts to decreasing levels.
    FLOAT32 attackCoeff;                          // Internal coefficient realizing the attack time.
    FLOAT32 releaseCoeff;                         // Internal coefficient realizing the release time.
    INT32 holdCount;                              // Hold time translated to the number of blocks
    FLOAT32* envState;                            // Vector of per-sample states of the envelope detectors
    INT32* holdState;                             // Vector of per-sample states of the envelope detectors
} ModuleSbAttackReleaseClass;

Variables

Properties

Name	Type	Usage	isHidden	Default value	Range	Units
attackTime	float	parameter	0	2	0:2000	msec
holdTime	float	parameter	0	100	0:1000	msec
releaseTime	float	parameter	0	100	0:1000	msec
attackCoeff	float	derived	1	0.01036	Unrestricted
releaseCoeff	float	derived	1	0.0002083	Unrestricted
holdCount	int	parameter	1	4800	Unrestricted
envState	float*	state	1	[32 x 1]	Unrestricted
holdState	int*	state	1	[32 x 1]	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

Output Pins

Name: out

Description: audio output

Data type: float

MATLAB Usage

File Name: sb_attack_release_module.m

 M=sb_attack_release_module(NAME)
 Subband envelope detector with programmable attack, release, and
 hold time constants.  Each input sample is treated as a separate
 channel rather than subsequent time values.  The module is applicable
 to subband processing for filterbanks.
 
 Arguments:
    NAME - name of the module.
 Copyright 2011.  DSP Concepts, Inc.  All Rights Reserved.