webdaw-modules/heartbeat/transpose.js

a set of modules for building a web-based DAW

function transpose() {

  'use strict';

  var
    // satisfy jslint
    Pitchshift = window.Pitchshift,

    context,
    fftFrameSize = 2048,
    shifter;

  function init() {
    if (window.Pitchshift) {
      shifter = new Pitchshift(fftFrameSize, context.sampleRate, 'FFT');
    }
  }


  function transpose(inputBuffer, semitones, cb) {
    if (shifter === undefined) {
      console.log('include Kiev II');
      return;
    }
    if (semitones === 0) {
      if (cb) {
        //console.log(inputBuffer, semitones)
        cb(inputBuffer);
        return;
      }
    }

    var numChannels = inputBuffer.numberOfChannels,
      c, input, length, output, outputs = [], shiftValue, i,
      outputBuffer;

    //console.log(inputBuffer);

    for (c = 0; c < numChannels; c++) {
      input = inputBuffer.getChannelData(c);
      length = input.length;
      output = new Float32Array(length);
      shiftValue = Math.pow(1.0595, semitones);
      //shiftValue = 1.01;
      shifter.process(shiftValue, input.length, 4, input);
      //shifter.process(shiftValue, input.length, 8, input);
      for (i = 0; i < length; i++) {
        output[i] = shifter.outdata[i];
      }
      outputs[c] = output;
    }

    outputBuffer = context.createBuffer(
      numChannels,
      length,
      inputBuffer.sampleRate
    );

    for (c = 0; c < numChannels; c++) {
      outputBuffer.getChannelData(c).set(outputs[c]);
    }

    cb(outputBuffer);
  }

  sequencer.protectedScope.transpose = transpose;

  sequencer.protectedScope.addInitMethod(function () {
    context = sequencer.protectedScope.context;
    init();
  });

}