@ircam/sc-signal

Simple signal processing utilities.

Install

npm install --save @ircam/sc-signal

API

Table of Contents

• Clipper
• Hysteresis
• Lowpass
• Scaler

Clipper

Represents a Clipper object that limits the range of input values.

Parameters

• $0 Object (optional, default {})

  • $0.min (optional, default -Infinity)
  • $0.max (optional, default Infinity)

• options Object? The options object.

Examples

// clip to [0,1]
const clipper = new Clipper({
 min: 0,
 max: 1,
});

clipper.process(0.5); // 0.5
clipper.process(2); // 1
clipper.process(-1); // 0

// min only
const clipper = new Clipper({
  min: 0,
});

clipper.process(0.5); // 0.5
clipper.process(2); // 2
clipper.process(-1); // 0

set

Sets the attributes of the Clipper object.

Parameters

• attributes Object The attributes to be set. Same as constructor options.

process

Processes the input value and returns the clipped value within the specified range.

Parameters

• inputValue number The input value to be processed.

Returns number The clipped value within the specified range.

Hysteresis

Represents an Hysteresis filter.

Parameters

• $0 Object (optional, default {})

  • $0.sampleRate (optional, default 2)
  • $0.lowpassFrequencyUp (optional, default 0.5)
  • $0.lowpassFrequencyDown (optional, default 0.5)

• options Object? The options object.

Examples

// hysteresis with quick up and slow down
const hysteresis = new Hysteresis({
 sampleRate: 2, // normalised frequency
 lowpassFrequencyUp: 0.9,
 lowpassFrequencyDown: 0.1,
});

hysteresis.process(0); // 0
hysteresis.process(1); // 0.9
hyteresis.process(1); // 0.99
hysteresis.process(1); // 0.999
hysteresis.process(1); // 0.9999
hysteresis.process(1); // 0.99999
hysteresis.process(1); // 0.999999
hysteresis.process(0); // 0.899999
hysteresis.process(0); // 0.809999
hysteresis.process(0); // 0.728999
hysteresis.process(0); // 0.656099
hysteresis.process(0); // 0.590489

set

Sets the attributes of the Hysteresis filter.

Parameters

• attributes Object The attributes to set. Same as constructor options.

init

Initializes the Hysteresis filter.

process

Processes the input value through the Hysteresis filter.

Parameters

• inputValue number The input value to process.

Returns number The output value of the Hysteresis filter.

reset

Resets the Hysteresis filter.

Lowpass

Represents a Lowpass filter.

Parameters

• $0 Object (optional, default {})

  • $0.sampleRate (optional, default 2)
  • $0.lowpassFrequency (optional, default 0.5)

• options Object? The options object.

Examples

const lowpass = new Lowpass({
sampleRate: 2, // normalised frequency
lowpassFrequency: 0.9,
});

lowpass.process(0); // 0
lowpass.process(1); // 0.9
lowpass.process(1); // 0.99
lowpass.process(1); // 0.999
lowpass.process(1); // 0.9999
lowpass.process(1); // 0.99999
lowpass.process(1); // 0.999999

set

Sets the attributes of the Lowpass filter.

Parameters

• attributes Object The attributes to set. Same as constructor options.

init

Initializes the Lowpass filter.

process

Processes the input value through the Lowpass filter.

Parameters

• inputValue number The input value to process.

Returns number The filtered output value.

reset

Resets the Lowpass filter.

Scaler

Represents a Scaler that maps values from an input range to an output range.

Parameters

• $0 Object (optional, default {})

  • $0.inputStart (optional, default 0)
  • $0.inputEnd (optional, default 1)
  • $0.outputStart (optional, default 0)
  • $0.outputEnd (optional, default 1)
  • $0.clip (optional, default false)
  • $0.type (optional, default 'linear')
  • $0.base (optional, default 1)

• options Object? The options object.

Examples

// linear
const scaler = new Scaler({
  inputStart: 0,
  inputEnd: 10,
  outputStart: 0,
  outputEnd: 100,
});

scaler.process(5); // 50
scaler.process(0); // 0
scaler.process(10); // 100

// MIDI pitch to Hertz
const scaler = new Scaler({
  inputStart: 69,
  inputEnd: 81,
  outputStart: 440,
  outputEnd: 880,
  type: 'exponential',
  base: 2,
  clip: false,
});

scaler.process(69); // 440
scaler.process(81); // 880
scaler.process(72); // 523.251131
scaler.process(93); // 1760 (no clipping)

// decibel to amplitude
const scaler = new Scaler({
  inputStart: 0,
  inputEnd: 20,
  outputStart: 1,
  outputEnd: 10,
  type: 'exponential',
  base: 10,
  clip: false,
});

scaler.process(0); // 1
scaler.process(20); // 10
scaler.process(-20); // 0.1 (no clipping)

set

Set the scaler attributes.

Parameters

• attributes Object The attributes to set. Same as constructor options.

init

Initialize the scaler.

process

Process the input value and return the scaled value.

Parameters

• inputValue number The input value to scale.

Returns number The scaled output value.

License

BSD-3-Clause