audio-frequency-tempered

Distributes the data returned from AnalyserNode.getByteFrequencyData() according to a logarithmic scale. Low frequency bins are shared by multiple bars, while high frequency ones are bundled together.

The technique comes from Henrique Vianna's audioMotion-analyzer.

Install

npm install audio-frequency-tempered

Example

const { createAudioBars, updateAudioBars } = require('audio-frequency-tempered');

// create audio context, analyser, data array
// omitted: source, gain, connect, etc.
const audioCtx = new AudioContext();
const analyser = audioCtx.createAnalyser();
const audioData = new Uint8Array(analyser.frequencyBinCount);

// create audio bars
const audioBars = createAudioBars({ groupLevel: 8 });

// on update
analyser.getByteFrequencyData(audioData);
updateAudioBars(audioData);

audioBars.forEach(bar => console.log(bar));

Output:

{ value: 0.6078, factor: 1, iniBin: 6, endBin: 9 }
{ value: 0.8196, factor: 1, iniBin: 10, endBin: 18 }
{ value: 0.8980, factor: 1, iniBin: 19, endBin: 37 }
{ value: 0.7254, factor: 1, iniBin: 38, endBin: 73 }
{ value: 0.5215, factor: 1, iniBin: 74, endBin: 146 }
{ value: 0.4352, factor: 1, iniBin: 147, endBin: 292 }
{ value: 0.4627, factor: 1, iniBin: 293, endBin: 584 }
{ value: 0.4313, factor: 1, iniBin: 585, endBin: 1167 }
{ value: 0.3411, factor: 1, iniBin: 1168, endBin: 2333 }
{ value: 0.0000, factor: 1, iniBin: 2334, endBin: 3110 }

Demo

audio-frequency-tempered demo

Usage

createAudioBars(options)

• options
  • groupLevel (default 5) 1 to 8, where 1 = 1/24 octave and 8 = full octave
  • sampleRate (default 44100) audioContext.sampleRate
  • frequencyBinCount (default 1024) analyser.frequencyBinCount
  • minFreq (default 20) minimum frequency (Hz)
  • maxFreq (default 22000) maximum frequency (Hz)

Returns an array of 'bar' objects { iniBin, endBin, factor, value }

• iniBin - initial bin of the analyser frequency data
• endBin - end bin of the analyser frequency data
• factor - interpolation factor - when multiple bars share the same bin
• value - normalised maximum energy value of the frequencies between iniBin and endBin

updateAudioBars(audioData)

• audioData Uint8Array passed to analyser.getByteFrequencyData

Returns null

getAudioBars()

Returns the previously created array of audio bars.

getAudioEnergy()

Returns the average audio energy (sum of bar values / number of bars).

See Also

• audioMotion-analyzer
• Creating a frequency bar graph

License

MIT, see LICENSE for details.