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128 lines
5.1 KiB
JavaScript
128 lines
5.1 KiB
JavaScript
// Copyright (C) 2013 Massachusetts Institute of Technology
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//
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// This program is free software; you can redistribute it and/or
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// modify it under the terms of the GNU General Public License version 2,
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// as published by the Free Software Foundation.
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//
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// This program is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU General Public License for more details.
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//
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// You should have received a copy of the GNU General Public License
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// along with this program; if not, write to the Free Software
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// Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
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// NotePlayer.js
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// Tim Mickel, 2013
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// Based entirely on the AS version by John Maloney
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//
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// Subclass of SoundDecoder to play notes on a sampled instrument or drum.
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//
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// A sampled instrument outputs interpolated sound samples from an array of signed,
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// 16-bit integers with an original sampling rate of 22050 samples/sec. The pitch is
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// shifted by change the step size while iterating through this array. An instrument
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// may also be looped so that it can be sustained and it may have a volume envelope
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// to control the attack and decay of the note.
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var NotePlayer = function(wavFileData, originalPitch, loopStart, loopEnd, env) {
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this.originalPitch = originalPitch || null;
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this.index = 0;
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this.samplesRemaining = 0; // determines note duration
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// Looping
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this.isLooped = false;
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this.loopPoint = 0; // final sample in loop
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this.loopLength = 0;
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// Volume Envelope
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this.envelopeValue = 1;
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this.samplesSinceStart = 0;
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this.attackEnd = 0;
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this.attackRate = 0;
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this.holdEnd = 0;
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this.decayRate = 1;
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if (wavFileData == null) wavFileData = new ArrayBuffer();
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var stepSize = 0.5; // default - no pitch shift
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var startOffset = 0;
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this.endOffset = wavFileData.byteLength / 2; // end of sample data
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var getSample = function() { return 0; } // called once at startup time
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this.soundData = new Uint8Array(wavFileData);
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if ((loopStart >= 0) && (loopStart < this.endOffset)) {
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this.isLooped = true;
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this.loopPoint = loopStart;
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if ((loopEnd > 0) && (loopEnd <= this.endOffset)) this.endOffset = loopEnd;
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this.loopLength = this.endOffset - this.loopPoint;
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// Compute the original pitch more exactly from the loop length:
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var oneCycle = 22050 / this.originalPitch;
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var cycles = Math.round(this.loopLength / oneCycle);
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this.originalPitch = 22050 / (this.loopLength / cycles);
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}
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if (env) {
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this.attackEnd = env[0] * 44.100;
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if (this.attackEnd > 0) this.attackRate = Math.pow(33000, 1 / this.attackEnd);
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this.holdEnd = this.attackEnd + (env[1] * 44.100);
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var decayCount = env[2] * 44100;
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this.decayRate = (decayCount == 0) ? 1 : Math.pow(33000, -1 / decayCount);
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}
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}
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NotePlayer.prototype = Object.create(SoundDecoder.prototype);
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NotePlayer.prototype.constructor = NotePlayer;
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NotePlayer.prototype.setNoteAndDuration = function(midiKey, secs) {
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midiKey = Math.max(0, Math.min(midiKey, 127));
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var pitch = 440 * Math.pow(2, (midiKey - 69) / 12); // midi key 69 is A (440 Hz)
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this.stepSize = pitch / (2 * this.originalPitch); // adjust for original sampling rate of 22050
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this.setDuration(secs);
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}
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NotePlayer.prototype.setDuration = function(secs) {
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this.samplesSinceStart = 0;
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this.samplesRemaining = 44100 * secs;
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if (!this.isLooped) this.samplesRemaining = Math.min(this.samplesRemaining, this.endOffset / this.stepSize);
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this.envelopeValue = (this.attackEnd > 0) ? 1 / 33000 : 1;
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}
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NotePlayer.prototype.interpolatedSample = function() {
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if (this.samplesRemaining-- <= 0) { this.noteFinished(); return 0; }
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this.index += this.stepSize;
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while (this.index >= this.endOffset) {
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if (!this.isLooped) return 0;
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this.index -= this.loopLength;
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}
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var i = Math.floor(this.index);
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var frac = this.index - i;
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var curr = this.rawSample(i);
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var next = this.rawSample(i + 1);
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var sample = (curr + (frac * (next - curr))) / 100000; // xxx 32000; attenuate...
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if (this.samplesRemaining < 1000) sample *= (this.samplesRemaining / 1000.0); // relaase phease
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this.updateEnvelope();
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return this.envelopeValue * sample;
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}
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NotePlayer.prototype.rawSample = function(sampleIndex) {
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if (sampleIndex >= this.endOffset) {
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if (this.isLooped) sampleIndex = this.loopPoint;
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else return 0;
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}
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var byteIndex = 2 * sampleIndex;
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var result = (this.soundData[byteIndex + 1] << 8) + this.soundData[byteIndex];
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return (result <= 32767) ? result : result - 65536;
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}
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NotePlayer.prototype.updateEnvelope = function() {
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// Compute envelopeValue for the current sample.
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this.samplesSinceStart++;
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if (this.samplesSinceStart < this.attackEnd) {
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this.envelopeValue *= this.attackRate;
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} else if (this.samplesSinceStart == this.attackEnd) {
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this.envelopeValue = 1;
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} else if (this.samplesSinceStart > this.holdEnd) {
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if (this.decayRate < 1) this.envelopeValue *= this.decayRate;
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}
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}
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