(8.D.2.5) AllpassDelayci
- David Buzzell (Unlicensed)
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. If the delay time is exactly equal to 0, the module essentially runs in a bypass mode. 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 https://dspconcepts.atlassian.net/wiki/spaces/DOCHUB/pages/3171189051 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 | Â |
stateIndex | int | state | 1 | 0 | Unrestricted | Â |
state | float* | state | 1 | [1 x 101] | Unrestricted | Â |
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
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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.Â