Feedback Delay

Overview

Recursive system implementing a feedback delay module

Discussion

This module implements a time-varying delay, with feedback gain control. The first input pin (mod) specifies the modulation factor; the second input pin is the multichannel audio signal. The module computes the instantaneous delay to apply on a sample-by-sample basis. The instantaneous delay is a floating-point value computed as:

delay[n] = M.currentDelay + mod[n] * M.modDepth

The modulation factor input is usually in the range [-1 +1], but this is not checked by the module.

The instantaneous delay time is a floating-point value and the module implements fractional sample interpolation using linear or cubic (third order) interpolation.

Module Pack

awe-mod-dspc-snd

ClassID

classID = 41825

Type Definition

typedef struct _ModuleFeedbackDelay
{
ModuleInstanceDescriptor instance;            // Common Audio Weaver module instance structure
INT32 maxDelay;                               // Maximum delay that can be realized, in samples.  The size of the delay buffer (maxDelay+1)*numChannels
INT32 interpType;                             // Interpolation type. 0 - Linear, 1 - Cubic
FLOAT32 currentDelay;                         // Current delay
FLOAT32 modDepth;                             // Maximum depth, in samples, of the modulation signal
FLOAT32 fGain;                                // Feedback gain.
INT32 stateIndex;                             // Index of the oldest state variable in the array of state variables
INT32 stateHeap;                              // Heap in which to allocate memory
FLOAT32* state;                               // State variable array
} ModuleFeedbackDelayClass;

Variables

Properties

Name	Type	Usage	isHidden	Default Value	Range	Units
maxDelay	int	const	0	100	1:100000	samples
interpType	int	const	0	0	0:1
currentDelay	float	parameter	0	0	0:100	samples
modDepth	float	parameter	0	0	0:100	samples
fGain	float	parameter	0	0.5	0:1
stateIndex	int	state	1	0	Unrestricted
stateHeap	int	const	1	561	Unrestricted
state	float*	state	1	[1 x 101]	Unrestricted

Pins

Input Pins


Name	mod
Description	modulation input
Data type	float
Channel range	1
Block size range	Unrestricted
Sample rate range	Unrestricted
Complex support	Real


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: feedback_delay_module.m 
 M=feedback_delay_module(NAME, MAXDELAY, MEMHEAP, INTERP_TYPE) 
 Creates a fractional sample time delay with feedback gain for use in the  
 Audio Weaver. 
 Arguments: 
    NAME - name of the module. 
    MAXDELAY - Maximum delay, in samples. 
    MEMHEAP - specifies the memory heap to use to allocate the main 
              state buffer.  This is a string and follows the memory 
              allocation enumeration in Framework.h.  Allowable values 
              are: 
              'AWE_HEAP_FAST' - always use internal DM memory. 
              'AWE_HEAP_FASTB' - always use internal PM memory. 
              'AWE_HEAP_SLOW' - always use external memory. 
              'AWE_HEAP_FAST2SLOW' - use internal memory.  If this fails 
              then use external memory (the default). 
              'AWE_HEAP_FASTB2SLOW' - use internal memory.  If this fails 
              then use external memory. 
    INTERP_TYPE - Interpolation type. Linear or Cubic.