Overview

High order allpass structure with fractional time delays

Discussion

An allpass interpolated delay module where the delay time is taken from the first input pin. The second input pin is the audio to process. The module supports fractional delay times and uses cubic interpolation between sample values. Delay times as small as 0 samples can be realized. The first input pin contains a single channel of data. The second input pin (audio) can be multichannel with the same processing applied to all channels. 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.

The delay time is determined by the value on the first input pin times the .modDepth parameter. In normal use, the delay input variable is in the range [0 1] while .modDepth is set to maxDelay. The delay time is updated every samples.

See AllpassDelayi for similar functionality but with linear interpolation.

Type Definition

typedef struct _ModuleAllpassDelayci
{
    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
    FLOAT32 currentDelay;                         // Current delay, in samples. This can be a non-integer number of samples.
    FLOAT32 modDepth;                             // Maximum depth, in samples, of the modulation signal
    FLOAT32 coef;                                 // Feedback/-feedforward coefficient for the allpass delay.
    INT32 stateIndex;                             // Index of the oldest state variable in the array of state variables
    FLOAT32* state;                               // State variable array
} ModuleAllpassDelayciClass;

Variables

Properties

Name	Type	Usage	isHidden	Default value	Range	Units
maxDelay	int	const	0	100	1:100000	samples
currentDelay	float	parameter	0	0	0:0.1:100	samples
modDepth	float	parameter	0	0	0:0.1:100	samples
coef	float	parameter	0	0.5	-1:1
stateIndex	int	state	1	0	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: allpass_delayci_module.m

 M=allpass_delayci_module(NAME, MAXDELAY)
 Creates a fractional sample allpass delay for use in the Audio Weaver.
 Arguments:
    NAME - name of the module.
    MAXDELAY - Maximum delay, in samples.