noises.lib

Faust Noise Generator Library. Its official prefix is no.

References

Functions Reference

(no.)noise

White noise generator (outputs random number between -1 and 1). noise is a standard Faust function.

Usage

noise : _

(no.)multirandom

Generates multiple decorrelated random numbers in parallel.

Usage

multirandom(N) : si.bus(N)

Where:

  • N: the number of decorrelated random numbers in parallel, a constant numerical expression

(no.)multinoise

Generates multiple decorrelated noises in parallel.

Usage

multinoise(N) : si.bus(N)

Where:

  • N: the number of decorrelated random numbers in parallel, a constant numerical expression

(no.)noises

A convenient wrapper around multinoise.

Usage

noises(N,i) : _

Where:

  • N: the number of decorrelated random numbers in parallel, a constant numerical expression
  • i: the selected random number (i in [0..N[)

(no.)randomseed

A random seed based on the foreign function arc4random (see man arc4random). Used in rnoise, rmultirandom, etc. to avoid having the same pseudo random sequence at each run.

WARNING: using the foreign function arc4random, so only available in C/C++ and LLVM backends.

Usage

randomseed : _

(no.)rnoise

A randomized white noise generator (outputs random number between -1 and 1).

WARNING: using the foreign function arc4random, so only available in C/C++ and LLVM backends.

Usage

rnoise : _

(no.)rmultirandom

Generates multiple decorrelated random numbers in parallel.

WARNING: using the foreign function arc4random, so only available in C/C++ and LLVM backends.

Usage

rmultirandom(N) : _

Where:

  • N: the number of decorrelated random numbers in parallel, a constant numerical expression

(no.)rmultinoise

Generates multiple decorrelated noises in parallel.

WARNING: using the foreign function arc4random, so only available in C/C++ and LLVM backends.

Usage

rmultinoise(N) : _

Where:

  • N: the number of decorrelated random numbers in parallel, a constant numerical expression

(no.)rnoises

A convenient wrapper around rmultinoise.

WARNING: using the foreign function arc4random, so only available in C/C++ and LLVM backends.

Usage

rnoises(N,i) : _

Where:

  • N: the number of decorrelated random numbers in parallel
  • i: the selected random number (i in [0..N[)

(no.)pink_noise

Pink noise (1/f noise) generator (third-order approximation covering the audio band well). pink_noise is a standard Faust function.

Usage

pink_noise : _

Reference

Alternatives

Higher-order approximations covering any frequency band can be obtained using

no.noise : fi.spectral_tilt(order,lowerBandLimit,Bandwidth,p)

where p=-0.5 means filter rolloff f^(-1/2) which gives 1/f rolloff in the power spectral density, and can be changed to other real values.

Example

// pink_noise_compare.dsp - compare three pinking filters

process = pink_noises with {
    f0 = 35; // Lower bandlimit in Hz
    bw3 = 0.7 * ma.SR/2.0 - f0; // Bandwidth in Hz, 3rd order case
    bw9 = 0.8 * ma.SR/2.0 - f0; // Bandwidth in Hz, 9th order case
    pink_tilt_3 = fi.spectral_tilt(3,f0,bw3,-0.5);
    pink_tilt_9 = fi.spectral_tilt(9,f0,bw9,-0.5);
    pink_noises = 1-1' <:
      no.pink_filter, // original designed by invfreqz in Octave
      pink_tilt_3,    // newer method using the same filter order
      pink_tilt_9;    // newer method using a higher filter order
};

Output of Example

faust2octave pink_noise_compare.dsp
Octave:1> semilogx(20*log10(abs(fft(faustout,8192))(1:4096,:)));
...

pink_noise_demo figure

(no.)pink_noise_vm

Multi pink noise generator.

Usage

pink_noise_vm(N) : _

Where:

  • N: number of latched white-noise processes to sum, not to exceed sizeof(int) in C++ (typically 32).

References

(no.)lfnoise, (no.)lfnoise0 and (no.)lfnoiseN

Low-frequency noise generators (Butterworth-filtered downsampled white noise).

Usage

lfnoise0(rate) : _   // new random number every int(ma.SR/rate) samples or so
lfnoiseN(N,rate) : _ // same as "lfnoise0(rate) : fi.lowpass(N,rate)" [see filters.lib]
lfnoise(rate) : _    // same as "lfnoise0(rate) : seq(i,5,fi.lowpass(N,rate))" (no overshoot)

Example

(view waveforms in faust2octave):

rate = ma.SR/100.0; // new random value every 100 samples (ma.SR from maths.lib)
process = lfnoise0(rate),   // sampled/held noise (piecewise constant)
          lfnoiseN(3,rate), // lfnoise0 smoothed by 3rd order Butterworth LPF
          lfnoise(rate);    // lfnoise0 smoothed with no overshoot

(no.)sparse_noise

Sparse noise generator.

Usage

sparse_noise(f0) : _

Where:

  • f0: average frequency of noise impulses per second

Random impulses in the amplitude range -1 to 1 are generated at an average rate of f0 impulses per second.

Reference

  • See velvet_noise

(no.)velvet_noise_vm

Velvet noise generator.

Usage

velvet_noise(amp, f0) : _

Where:

  • amp: amplitude of noise impulses (positive and negative)
  • f0: average frequency of noise impulses per second

Reference

  • Matti Karjalainen and Hanna Jarvelainen, "Reverberation Modeling Using Velvet Noise", in Proc. 30th Int. Conf. Intelligent Audio Environments (AES07), March 2007.

(no.)gnoise

Approximate zero-mean, unit-variance Gaussian white noise generator.

Usage

gnoise(N) : _

Where:

  • N: number of uniform random numbers added to approximate Gaussian white noise

Reference

  • See Central Limit Theorem

(no.)colored_noise

Generates a colored noise signal with an arbitrary spectral roll-off factor (alpha) over the entire audible frequency range (20-20000 Hz). The output is normalized so that an equal RMS level is maintained for different values of alpha.

Usage

colored_noise(N,alpha) : _

Where:

  • N: desired integer filter order (constant numerical expression)
  • alpha: slope of roll-off, between -1 and 1. -1 corresponds to brown/red noise, -1/2 pink noise, 0 white noise, 1/2 blue noise, and 1 violet/azure noise.

Examples

See dm.colored_noise_demo.