Overview

Sample-based time delay

Discussion

An allpass fractional delay module, where the delay is specified as an integer number of samples. The delay is implemented such that delays as short as 0 samples can be realized. The module has one multichannel input and one multichannel output. The module can operate on multiple channels and applies the same delay to each channel. The delay line is incorporated into a first order allpass topology (transposed Direct Form II), with the feedback gain determined by the coef value, and the feedforward gain determined by -coef.

At construction time, you specify the maximum delay (maxDelay) of the module. maxDelay determines the size of the internal state buffer. To be precise, the size of the internal state buffer equals (maxDelay+1)*numChannels. In addition, you specify the instantaneous delay through the interface variable .currentDelay. currentDelay is in the range [0 maxDelay] and can be changed at run-time. Note that the module is not smoothly updating and you may get audible clicks when adjusting the currentDelay at run-time.

Type Definition

typedef struct _ModuleAllpassDelayFract32
{
    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 currentDelay;                           // Current delay
    FLOAT32 coef;                                 // Feedback/-feedforward coefficient for the allpass delay.
    fract32 coefFract32;                          // Feedback/-feedforward fractional coefficient for the allpass delay.
    INT32 postShift;                              // Number of bits to shift after the fractional multiply. This is based on gain.range.
    INT32 stateIndex;                             // Index of the oldest state variable in the array of state variables
    fract32* state;                               // State variable array
} ModuleAllpassDelayFract32Class;

Variables

Properties

Name	Type	Usage	isHidden	Default value	Range	Units
maxDelay	int	const	0	100	1:100000	samples
currentDelay	int	parameter	0	0	0:1:100	samples
coef	float	parameter	0	0.5	-1:1
coefFract32	fract32	derived	0	0.5	Unrestricted
postShift	int	derived	1	0	Unrestricted
stateIndex	int	state	1	0	Unrestricted
state	fract32*	state	1	[1 x 101]	Unrestricted

Pins

Input Pins

Name: in

Description: audio input

Data type: fract32

Channel range: Unrestricted

Block size range: Unrestricted

Sample rate range: Unrestricted

Complex support: Real

Output Pins

Name: out

Description: audio output

Data type: fract32

MATLAB Usage

File Name: allpass_delay_fract32_module.m

 M=allpass_delay_fract32_module(NAME, MAXDELAY)
 Delay based allpass (1st order), using integer length delay.  Arguments:
 Arguments:
    NAME - name of the module.
    MAXDELAY - Maximum delay, in samples.