doing this

1 files changed, 184 insertions, 0 deletions

diff --git a/synth.js b/synth.js
new file mode 100644
index 0000000..ac05cb3
--- /dev/null
+++ b/synth.js
@@ -0,0 +1,184 @@
+function SineGenerator(freq) {
+	var self = {'alive': true};
+	var period = sampleRate / freq;
+	var t = 0;
+	
+	self.generate = function(buf, offset, count) {
+		for (; count; count--) {
+			var phase = t / period;
+			var result = Math.sin(phase * 2 * Math.PI);
+			buf[offset++] += result;
+			buf[offset++] += result;
+			t++;
+		}
+	}
+	
+	return self;
+}
+
+function SquareGenerator(freq, phase) {
+	var self = {'alive': true};
+	var period = sampleRate / freq;
+	var t = 0;
+	
+	self.generate = function(buf, offset, count) {
+		for (; count; count--) {
+			var result = ( (t / period) % 1 > phase ? 1 : -1);
+			buf[offset++] += result;
+			buf[offset++] += result;
+			t++;
+		}
+	}
+	
+	return self;
+}
+
+function ADSRGenerator(child, attackAmplitude, sustainAmplitude, attackTimeS, decayTimeS, releaseTimeS) {
+	var self = {'alive': true}
+	var attackTime = sampleRate * attackTimeS;
+	var decayTime = sampleRate * (attackTimeS + decayTimeS);
+	var decayRate = (attackAmplitude - sustainAmplitude) / (decayTime - attackTime);
+	var releaseTime = null; /* not known yet */
+	var endTime = null; /* not known yet */
+	var releaseRate = sustainAmplitude / (sampleRate * releaseTimeS);
+	var t = 0;
+	
+	self.noteOff = function() {
+		if (self.released) return;
+		releaseTime = t;
+		self.released = true;
+		endTime = releaseTime + sampleRate * releaseTimeS;
+	}
+	
+	self.generate = function(buf, offset, count) {
+		if (!self.alive) return;
+		var input = new Array(count * 2);
+		for (var i = 0; i < count*2; i++) {
+			input[i] = 0;
+		}
+		child.generate(input, 0, count);
+		
+		childOffset = 0;
+		while(count) {
+			if (releaseTime != null) {
+				if (t < endTime) {
+					/* release */
+					while(count && t < endTime) {
+						var ampl = sustainAmplitude - releaseRate * (t - releaseTime);
+						buf[offset++] += input[childOffset++] * ampl;
+						buf[offset++] += input[childOffset++] * ampl;
+						t++;
+						count--;
+					}
+				} else {
+					/* dead */
+					self.alive = false;
+					return;
+				}
+			} else if (t < attackTime) {
+				/* attack */
+				while(count && t < attackTime) {
+					var ampl = attackAmplitude * t / attackTime;
+					buf[offset++] += input[childOffset++] * ampl;
+					buf[offset++] += input[childOffset++] * ampl;
+					t++;
+					count--;
+				}
+			} else if (t < decayTime) {
+				/* decay */
+				while(count && t < decayTime) {
+					var ampl = attackAmplitude - decayRate * (t - attackTime);
+					buf[offset++] += input[childOffset++] * ampl;
+					buf[offset++] += input[childOffset++] * ampl;
+					t++;
+					count--;
+				}
+			} else {
+				/* sustain */
+				while(count) {
+					buf[offset++] += input[childOffset++] * sustainAmplitude;
+					buf[offset++] += input[childOffset++] * sustainAmplitude;
+					t++;
+					count--;
+				}
+			}
+		}
+	}
+	
+	return self;
+}
+
+function midiToFrequency(note) {
+	return 440 * Math.pow(2, (note-69)/12);
+}
+
+PianoProgram = {
+	'attackAmplitude': 0.2,
+	'sustainAmplitude': 0.1,
+	'attackTime': 0.02,
+	'decayTime': 0.3,
+	'releaseTime': 0.02,
+	'createNote': function(note, velocity) {
+		var frequency = midiToFrequency(note);
+		return ADSRGenerator(
+			SineGenerator(frequency),
+			this.attackAmplitude * (velocity / 128), this.sustainAmplitude * (velocity / 128),
+			this.attackTime, this.decayTime, this.releaseTime
+		);
+	}
+}
+
+StringProgram = {
+	'createNote': function(note, velocity) {
+		var frequency = midiToFrequency(note);
+		return ADSRGenerator(
+			SineGenerator(frequency),
+			0.5 * (velocity / 128), 0.2 * (velocity / 128),
+			0.4, 0.8, 0.4
+		);
+	}
+}
+
+PROGRAMS = {
+	41: StringProgram,
+	42: StringProgram,
+	43: StringProgram,
+	44: StringProgram,
+	45: StringProgram,
+	46: StringProgram,
+	47: StringProgram,
+	49: StringProgram,
+	50: StringProgram
+};
+
+function Synth(sampleRate) {
+	
+	var generators = [];
+	
+	function addGenerator(generator) {
+		generators.push(generator);
+	}
+	
+	function generate(samples) {
+		var data = new Array(samples*2);
+		generateIntoBuffer(samples, data, 0);
+		return data;
+	}
+	
+	function generateIntoBuffer(samplesToGenerate, buffer, offset) {
+		for (var i = offset; i < offset + samplesToGenerate * 2; i++) {
+			buffer[i] = 0;
+		}
+		for (var i = generators.length - 1; i >= 0; i--) {
+			generators[i].generate(buffer, offset, samplesToGenerate);
+			if (!generators[i].alive) generators.splice(i, 1);
+		}
+	}
+	
+	return {
+		'sampleRate': sampleRate,
+		'addGenerator': addGenerator,
+		'generate': generate,
+		'generateIntoBuffer': generateIntoBuffer
+	}
+}