audio-buffer-remix

Upmix or downmix channels in AudioBuffer or AudioBufferList by the following table:

| Input Channels | Output Channels | Rules | |---|---|---| | 1 (Mono) | 2 (Stereo) | output[0] = input[0]output[1] = input[0] | | 1 (Mono) | 4 (Quad) | output[0] = input[0]output[1] = input[0]output[2] = 0output[3] = 0 | | 1 (Mono) | 6 (5.1) | output[0] = 0output[1] = 0output[2] = input[0]output[3] = 0output[4] = 0output[5] = 0 | | 2 (Stereo) | 1 (Mono) | output[0] = 0.5 * (input[0] + input[1]) | | 2 (Stereo) | 4 (Quad) | output[0] = input[0]output[1] = input[1]output[2] = 0output[3] = 0 | | 2 (Stereo) | 6 (5.1) | output[0] = input[0]output[1] = input[1]output[2] = 0output[3] = 0output[4] = 0output[5] = 0 | | 4 (Quad) | 1 (Mono) | output[0] = 0.25 * (input[0] + input[1] + input[2] + input[3]) | | 4 (Quad) | 2 (Stereo) | output[0] = 0.5 * (input[0] + input[2])output[1] = 0.5 * (input[1] + input[3]) | | 4 (Quad) | 6 (5.1) | output[0] = input[0]output[1] = input[1]output[2] = 0output[3] = 0output[4] = input[2]output[5] = input[3] | | 6 (5.1) | 1 (Mono) | output[0] = 0.7071 * (input[0] + input[1]) + input[2] + 0.5 * (input[2] + input[3]) | | 6 (5.1) | 2 (Stereo) | output[0] = input[0] + 0.7071 * (input[2] + input[4])output[1] = input[1] + 0.7071 * (input[2] + input[5]) | | 6 (5.1) | 4 (Quad) | output[0] = input[0] + 0.7071 * input[2]output[1] = input[1] + 0.7071 * input[2]output[2] = input[4]output[3] = input[5] | | n | m | output[n] = input[n] |

Usage

const AudioBuffer = require('audio-buffer')
const remix = require('audio-buffer-remix')

let stereoBuffer = new AudioBuffer(2, 1024)

quadBuffer = remix(stereoBuffer, 4)

API

let dest = remix(source, channels|map, interpretation|{context, interpretation}?)

Take source audio buffer and upmix/downmix its channels to dest with the indicated number of channels. options may provide audio context or interpretation type: 'discrete' or 'speaker', see channelInterpretation MDN reference.

Alternatively pass map − a list or object with channel mapping. Numbers as values map channels directly by numbers, null drops channel from output and function with (destChannelData, source) => {} signature expects to fill destChannelData array.

const util = require('audio-buffer-utils')

let source = util.noise(util.create(1024, 2))

let dest = remix(source, {
    //0 output channel - take first input channel data
    0: 1,

    //1 output channel - mute the data
    1: null,

    //2 output channel - mix 0 + 1 channels
    2: (destChannel, source) => {
        let left = source.getChannelData(0)
        let right = source.getChannelData(1)
        for (let i = 0; i < out.length; i++) {
            destChannel[i] = left[i] * .5 + right[i] * .5
        }
    }
})

dest.numberOfChannels // 3

See also

• audio — high-level class for audio
• audio-buffer — audio buffer class for nodejs and browser
• audio-buffer-list — audio buffer class for nodejs and browser
• audio-buffer-utils — toolset for audio buffers