delays.lib

This library contains a collection of delay functions. Its official prefix is de.

References

• https://github.com/grame-cncm/faustlibraries/blob/master/delays.lib

Basic Delay Functions

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(de.)delay

Simple d samples delay where n is the maximum delay length as a number of samples. Unlike the @ delay operator, here the delay signal d is explicitly bounded to the interval [0..n]. The consequence is that delay will compile even if the interval of d can't be computed by the compiler. delay is a standard Faust function.

Usage

_ : delay(n,d) : _

Where:

• n: the max delay length in samples
• d: the delay length in samples (integer)

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(de.)fdelay

Simple d samples fractional delay based on 2 interpolated delay lines where n is the maximum delay length as a number of samples. fdelay is a standard Faust function.

Usage

_ : fdelay(n,d) : _

Where:

• n: the max delay length in samples
• d: the delay length in samples (float)

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(de.)sdelay

s(mooth)delay: a mono delay that doesn't click and doesn't transpose when the delay time is changed.

Usage

_ : sdelay(n,it,d) : _

Where:

• n: the max delay length in samples
• it: interpolation time (in samples), for example 1024
• d: the delay length in samples (float)

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(de.)prime_power_delays

Prime Power Delay Line Lengths.

Usage

si.bus(N) : prime_power_delays(N,pathmin,pathmax) : si.bus(N);

Where:

• N: positive integer up to 16 (for higher powers of 2, extend 'primes' array below)
• pathmin: minimum acoustic ray length in the reverberator (in meters)
• pathmax: maximum acoustic ray length (meters) - think "room size"

Reference

• https://ccrma.stanford.edu/~jos/pasp/Prime_Power_Delay_Line.html

Lagrange Interpolation

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(de.)fdelaylti and (de.)fdelayltv

Fractional delay line using Lagrange interpolation.

Usage

_ : fdelaylt[i|v](N, n, d) : _

Where:

• N=1,2,3,... is the order of the Lagrange interpolation polynomial (constant numerical expression)
• n: the max delay length in samples
• d: the delay length in samples

fdelaylti is most efficient, but designed for constant/slowly-varying delay. fdelayltv is more expensive and more robust when the delay varies rapidly.

Note: the requested delay should not be less than (N-1)/2.

References

• https://ccrma.stanford.edu/~jos/pasp/Lagrange_Interpolation.html
• fixed-delay case
• variable-delay case
• Timo I. Laakso et al., "Splitting the Unit Delay - Tools for Fractional Delay Filter Design", IEEE Signal Processing Magazine, vol. 13, no. 1, pp. 30-60, Jan 1996.
• Philippe Depalle and Stephan Tassart, "Fractional Delay Lines using Lagrange Interpolators", ICMC Proceedings, pp. 341-343, 1996.

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(de.)fdelay[N]

For convenience, fdelay1, fdelay2, fdelay3, fdelay4, fdelay5 are also available where N is the order of the interpolation, built using fdelayltv.

Thiran Allpass Interpolation

Thiran Allpass Interpolation.

Reference

• https://ccrma.stanford.edu/~jos/pasp/Thiran_Allpass_Interpolators.html

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(de.)fdelay[N]a

Delay lines interpolated using Thiran allpass interpolation.

Usage

_ : fdelay[N]a(n, d) : _

(exactly like fdelay)

Where:

• N=1,2,3, or 4 is the order of the Thiran interpolation filter (constant numerical expression), and the delay argument is at least N-1/2. First-order: d at least 0.5, second-order: d at least 1.5, third-order: d at least 2.5, fourth-order: d at least 3.5.
• n: the max delay length in samples
• d: the delay length in samples

Note

The interpolated delay should not be less than N-1/2. (The allpass delay ranges from N-1/2 to N+1/2). This constraint can be alleviated by altering the code, but be aware that allpass filters approach zero delay by means of pole-zero cancellations.

Delay arguments too small will produce an UNSTABLE allpass!

Because allpass interpolation is recursive, it is not as robust as Lagrange interpolation under time-varying conditions (you may hear clicks when changing the delay rapidly).