misceffects - Faust Libraries

# misceffects.lib

This library contains a collection of audio effects. Its official prefix is `ef`.

## Dynamic

### `(ef.)cubicnl`

Cubic nonlinearity distortion. `cubicnl` is a standard Faust library.

#### Usage:

    _ : cubicnl(drive,offset) : _
    _ : cubicnl_nodc(drive,offset) : _

Where:

- `drive`: distortion amount, between 0 and 1
- `offset`: constant added before nonlinearity to give even harmonics. Note: offset can introduce a nonzero mean - feed cubicnl output to dcblocker to remove this.

#### References:

- https://ccrma.stanford.edu/~jos/pasp/Cubic_Soft_Clipper.html
- https://ccrma.stanford.edu/~jos/pasp/Nonlinear_Distortion.html

### `(ef.)gate_mono`

Mono signal gate. `gate_mono` is a standard Faust function.

#### Usage

    _ : gate_mono(thresh,att,hold,rel) : _

Where:

- `thresh`: dB level threshold above which gate opens (e.g., -60 dB)
- `att`: attack time = time constant (sec) for gate to open (e.g., 0.0001 s = 0.1 ms)
- `hold`: hold time = time (sec) gate stays open after signal level < thresh (e.g., 0.1 s)
- `rel`: release time = time constant (sec) for gate to close (e.g., 0.020 s = 20 ms)

#### References

- http://en.wikipedia.org/wiki/Noise_gate
- http://www.soundonsound.com/sos/apr01/articles/advanced.asp
- http://en.wikipedia.org/wiki/Gating_(sound_engineering)

### `(ef.)gate_stereo`

Stereo signal gates. `gate_stereo` is a standard Faust function.

#### Usage

     _,_ : gate_stereo(thresh,att,hold,rel) : _,_

Where:

- `thresh`: dB level threshold above which gate opens (e.g., -60 dB)
- `att`: attack time = time constant (sec) for gate to open (e.g., 0.0001 s = 0.1 ms)
- `hold`: hold time = time (sec) gate stays open after signal level < thresh (e.g., 0.1 s)
- `rel`: release time = time constant (sec) for gate to close (e.g., 0.020 s = 20 ms)

#### References

- http://en.wikipedia.org/wiki/Noise_gate
- http://www.soundonsound.com/sos/apr01/articles/advanced.asp
- http://en.wikipedia.org/wiki/Gating_(sound_engineering)

## Filtering

### `(ef.)speakerbp`

Dirt-simple speaker simulator (overall bandpass eq with observed roll-offs above and below the passband).

Low-frequency speaker model = +12 dB/octave slope breaking to flat near f1. Implemented using two dc blockers in series.

High-frequency model = -24 dB/octave slope implemented using a fourth-order Butterworth lowpass.

Example based on measured Celestion G12 (12" speaker):

`speakerbp` is a standard Faust function

#### Usage

    speakerbp(f1,f2)
    _ : speakerbp(130,5000) : _

### `(ef.)piano_dispersion_filter`

Piano dispersion allpass filter in closed form.

#### Usage

    piano_dispersion_filter(M,B,f0)
    _ : piano_dispersion_filter(1,B,f0) : +(totalDelay),_ : fdelay(maxDelay) : _

Where:

- `M`: number of first-order allpass sections (compile-time only) Keep below 20. 8 is typical for medium-sized piano strings.
- `B`: string inharmonicity coefficient (0.0001 is typical)
- `f0`: fundamental frequency in Hz

#### Outputs

- MINUS the estimated delay at `f0` of allpass chain in samples, provided in negative form to facilitate subtraction from delay-line length.
- Output signal from allpass chain

#### Reference

- "Dispersion Modeling in Waveguide Piano Synthesis Using Tunable Allpass Filters", by Jukka Rauhala and Vesa Valimaki, DAFX-2006, pp. 71-76
- http://lib.tkk.fi/Diss/2007/isbn9789512290666/article2.pdf An erratum in Eq. (7) is corrected in Dr. Rauhala's encompassing dissertation (and below).
- http://www.acoustics.hut.fi/research/asp/piano/

### `(ef.)stereo_width`

Stereo Width effect using the Blumlein Shuffler technique. `stereo_width` is a standard Faust function.

#### Usage

    _,_ : stereo_width(w) : _,_

Where:

- `w`: stereo width between 0 and 1

At `w=0`, the output signal is mono ((left+right)/2 in both channels). At `w=1`, there is no effect (original stereo image). Thus, w between 0 and 1 varies stereo width from 0 to "original".

#### Reference

- "Applications of Blumlein Shuffling to Stereo Microphone Techniques" Michael A. Gerzon, JAES vol. 42, no. 6, June 1994

## Meshes

### `(ef.)mesh_square`

Square Rectangular Digital Waveguide Mesh.

#### Usage

    bus(4*N) : mesh_square(N) : bus(4*N);

Where:

- `N`: number of nodes along each edge - a power of two (1,2,4,8,...)

#### Reference

- https://ccrma.stanford.edu/~jos/pasp/Digital_Waveguide_Mesh.html

#### Signal Order In and Out

The mesh is constructed recursively using 2x2 embeddings. Thus, the top level of `mesh_square(M)` is a block 2x2 mesh, where each block is a `mesh(M/2)`. Let these blocks be numbered 1,2,3,4 in the geometry NW,NE,SW,SE, i.e., as 1 2 3 4 Each block has four vector inputs and four vector outputs, where the length of each vector is `M/2`. Label the input vectors as Ni,Ei,Wi,Si, i.e., as the inputs from the North, East South, and West, and similarly for the outputs. Then, for example, the upper left input block of M/2 signals is labeled 1Ni. Most of the connections are internal, such as 1Eo -> 2Wi. The `8*(M/2)` input signals are grouped in the order 1Ni 2Ni 3Si 4Si 1Wi 3Wi 2Ei 4Ei and the output signals are 1No 1Wo 2No 2Eo 3So 3Wo 4So 4Eo or

In: 1No 1Wo 2No 2Eo 3So 3Wo 4So 4Eo

Out: 1Ni 2Ni 3Si 4Si 1Wi 3Wi 2Ei 4Ei

Thus, the inputs are grouped by direction N,S,W,E, while the outputs are grouped by block number 1,2,3,4, which can also be interpreted as directions NW, NE, SW, SE. A simple program illustrating these orderings is `process = mesh_square(2);`.

#### Example

Reflectively terminated mesh impulsed at one corner:

    mesh_square_test(N,x) = mesh_square(N)~(busi(4*N,x)) // input to corner
    with { busi(N,x) = bus(N) : par(i,N,*(-1)) : par(i,N-1,_), +(x); };
    process = 1-1' : mesh_square_test(4); // all modes excited forever

In this simple example, the mesh edges are connected as follows:

1No -> 1Ni, 1Wo -> 2Ni, 2No -> 3Si, 2Eo -> 4Si,

3So -> 1Wi, 3Wo -> 3Wi, 4So -> 2Ei, 4Eo -> 4Ei

A routing matrix can be used to obtain other connection geometries.

### `(ef.)reverseEchoN(nChans,delay)`

Reverse echo effect

#### Usage

    _ : ef.reverseEchoN(N,delay) : si.bus(N)

Where:

- `N`: Number of channels desired (1 or more)
- `delay`: echo delay (integer power of 2)

#### Demo

    _ : dm.reverseEchoN(N) : _,_

#### Description

The effect uses N instances of reverseDelayRamped at different phases.

### `(ef.)reverseDelayRamped(delay,phase)`

Reverse delay with amplitude ramp

#### Usage

    _ : ef.reverseDelayRamped(delay,phase) : _

Where:

- `delay`: echo delay (integer power of 2)
- `phase`: float between 0 and 1 giving ramp delay phase*delay

#### Demo

    _ : dm.reverseEchoN(N) : _,_

### `(ef.)uniformPanToStereo(nChans)`

Pan nChans channels to the stereo field, spread uniformly left to right

#### Usage

    si.bus(N) : ef.uniformPanToStereo(N) : _,_

Where:

- `N`: Number of input channels to pan down to stereo

#### Demo

    _ : dm.reverseEchoN(N) : _,_

## Time Based

### `(ef.)echo`

A simple echo effect.

`echo` is a standard Faust function

#### Usage

    _ : echo(maxDuration,duration,feedback) : _

Where:

- `maxDuration`: the max echo duration in seconds
- `duration`: the echo duration in seconds
- `feedback`: the feedback coefficient

## Pitch Shifting

### `(ef.)transpose`

A simple pitch shifter based on 2 delay lines. `transpose` is a standard Faust function.

#### Usage

    _ : transpose(w, x, s) : _

Where:

- `w`: the window length (samples)
- `x`: crossfade duration duration (samples)
- `s`: shift (semitones)

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