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stretch.js
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stretch.js
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/*
Vex.DSP - Signal Processing Libraries for VexFlow
Copyright 2014 Mohit Cheppudira.
STFT, Phase Vocoder implementations.
*/
define(['dsp', 'tools'],
function(dsp, tools) {
var TimeStretcher = (function() {
var DEBUG = true;
var DSP = dsp.DSP;
var FFT = dsp.FFT;
var WindowFunction = dsp.WindowFunction;
function L() { // Logger
if (DEBUG) console.log(Array.prototype.slice.call(arguments).join(" "));}
function TimeStretcher(options) {
this.init(options);
}
function onProgress(details, message) {
if (!message) message = "";
tools.onProgress(details, message);
}
function phase(fft, bin) {
return Math.atan2(fft.imag[bin], fft.real[bin]);
}
TimeStretcher.prototype = {
init: function(options) {
this.options = {
vocode: false, // Enable Phase Vocoder
stftBins: 8192, // Number of bins used by FFT
stftHop: 1/4, // Hop size for STFT (25%)
stretchFactor: 1.5, // Stretch factor (1.5x)
sampleRate: 44100, // PCM sample rate (44KHz)
progressCallback: onProgress
}
tools.merge(this.options, options);
this.stretched_buffer = null;
this.resampled_buffer = null;
return this;
},
setBuffer: function(buffer, sampleRate) {
this.buffer = buffer;
this.stretched_buffer = null;
this.resampled_buffer = null;
if (sampleRate) this.options.sampleRate = sampleRate;
return this;
},
getBuffer: function() {
return this.buffer;
},
getStretchFactor: function() {
return this.options.stretchFactor;
},
getStretchedBuffer: function() {
return this.stretched_buffer;
},
getPitchShiftedBuffer: function() {
return this.resampled_buffer;
},
getOptions: function() {
return this.options;
},
stretch: function() {
if (!this.buffer) {
throw "Error: TimeStretcher.setBuffer() must be called before stretch()"
}
if (this.stretched_buffer) return this.stretched_buffer;
var that = this;
function progress(stage, window, total_windows, complete) {
that.options.progressCallback({
current_stage: stage,
total_stages: 2,
current_window: window,
total_windows: total_windows,
complete: (complete == true)
}, "Time Stretching: ")
}
var points = this.options.stftBins;
var vocode = this.options.vocode;
var hop = parseInt(points * this.options.stftHop);
var hop_synthesis = parseInt(hop * this.options.stretchFactor);
var freq = this.options.sampleRate;
var data = this.buffer;
var t = 1 / freq;
var length = data.length;
var hanning = new WindowFunction(DSP.HANN);
var stretch_amount = this.options.stretchFactor;
L("Starting time stretch ("+ (stretch_amount) +"x). Buffer size: " + length);
var frames_processed = 0;
var output_frames = [];
// Analysis Phase: Perform STFT, and calculate phase adjustments.
for (var start = 0; start < (length - points); start += hop) { //
var section = new Float32Array(points);
section.set(data.subarray(start, start + points));
if (section.length < points) break;
if (vocode) {
var fft = new FFT(points, freq);
fft.forward(hanning.process(section));
output_frames.push(fft);
var this_frame = fft;
frames_processed++;
if (frames_processed > 1) {
var last_frame = output_frames[frames_processed - 2];
// For each bin
for (var bin = 0; bin < points; ++bin) { // only work on the lower freqs
var phase_shift = phase(this_frame, bin) - phase(last_frame, bin);
var freq_deviation = (phase_shift / (hop / freq)) - fft.getBandFrequency(bin);
var wrapped_deviation = ((freq_deviation + Math.PI) % (2 * Math.PI)) - Math.PI;
var true_freq = fft.getBandFrequency(bin) + wrapped_deviation;
var new_phase = phase(last_frame, bin) + ((hop_synthesis / freq) * true_freq);
// Calculate new spectrum
var new_mag = Math.sqrt(
(this_frame.real[bin] * this_frame.real[bin]) +
(this_frame.imag[bin] * this_frame.imag[bin]));
this_frame.real[bin] = new_mag * Math.cos(new_phase);
this_frame.imag[bin] = new_mag * Math.sin(new_phase);
}
}
} else {
output_frames.push(hanning.process(section));
frames_processed++;
}
progress(1, frames_processed, parseInt(((length - points) / hop)));
}
L("Analysis complete: " + frames_processed + " frames.")
// Synthesis Phase
var final_buffer = new Float32Array(parseInt(length * stretch_amount));
var overlap_pointer = 0;
var total_output = 0;
for (var i = 0; i < output_frames.length; ++i) {
var fft = output_frames[i];
var buffer = vocode ? hanning.process(fft.inverse()) : fft;
// var buffer = hanning.process(vocode ? fft.inverse() : fft);
for (var j = 0; j < buffer.length; ++j) {
final_buffer[overlap_pointer + j] += buffer[j];
}
total_output += buffer.length;
overlap_pointer += hop_synthesis;
progress(2, i + 1, output_frames.length);
}
progress(2, output_frames.length, output_frames.length, true);
this.stretched_buffer = final_buffer;
return this;
},
resize: function(size) {
var buffer = this.stretched_buffer;
var newBuffer = new Float32Array(size);
this.resampled_buffer = tools.interpolateArray(buffer, newBuffer, size);
return this;
}
}
return TimeStretcher;
})()
return {TimeStretcher: TimeStretcher}
});