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/*
* Copyright 2009 Phil Burk, Mobileer Inc
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.jsyn.unitgen;
/**
* Sine oscillator generates a frequency controlled sine wave. It is implemented using a fast Taylor
* expansion.
*
* @author Phil Burk (C) 2009 Mobileer Inc
*/
public class SineOscillator extends UnitOscillator {
public SineOscillator() {
}
public SineOscillator(double freq) {
frequency.set(freq);
}
public SineOscillator(double freq, double amp) {
frequency.set(freq);
amplitude.set(amp);
}
@Override
public void generate(int start, int limit) {
double[] frequencies = frequency.getValues();
double[] amplitudes = amplitude.getValues();
double[] outputs = output.getValues();
double currentPhase = phase.getValue();
for (int i = start; i < limit; i++) {
/* Generate sawtooth phasor to provide phase for sine generation. */
double phaseIncrement = convertFrequencyToPhaseIncrement(frequencies[i]);
currentPhase = incrementWrapPhase(currentPhase, phaseIncrement);
if (true) {
double value = fastSin(currentPhase);
outputs[i] = value * amplitudes[i];
} else {
// Slower but more accurate implementation.
outputs[i] = Math.sin(currentPhase * Math.PI) * amplitudes[i];
}
}
phase.setValue(currentPhase);
}
/**
* Calculate sine using Taylor expansion. Do not use values outside the range.
*
* @param currentPhase in the range of -1.0 to +1.0 for one cycle
*/
public static double fastSin(double currentPhase) {
// Factorial constants so code is easier to read.
final double IF3 = 1.0 / (2 * 3);
final double IF5 = IF3 / (4 * 5);
final double IF7 = IF5 / (6 * 7);
final double IF9 = IF7 / (8 * 9);
final double IF11 = IF9 / (10 * 11);
/* Wrap phase back into region where results are more accurate. */
double yp = (currentPhase > 0.5) ? 1.0 - currentPhase : ((currentPhase < (-0.5)) ? (-1.0)
- currentPhase : currentPhase);
double x = yp * Math.PI;
double x2 = (x * x);
/* Taylor expansion out to x**11/11! factored into multiply-adds */
double fastsin = x
* (x2 * (x2 * (x2 * (x2 * ((x2 * (-IF11)) + IF9) - IF7) + IF5) - IF3) + 1);
return fastsin;
}
}
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