FeedbackDelay

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.

Type Definition

CODE

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

CODE

 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.