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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;
/**
* Sawtooth DPW oscillator (a sawtooth with reduced aliasing).
* Based on a paper by Antti Huovilainen and Vesa Valimaki:
* http://www.scribd.com/doc/33863143/New-Approaches-to-Digital-Subtractive-Synthesis
*
* @author Phil Burk and Lisa Tolentino (C) 2009 Mobileer Inc
*/
public class SawtoothOscillatorDPW extends UnitOscillator {
// At a very low frequency, switch from DPW to raw sawtooth.
private static final double VERY_LOW_FREQUENCY = 2.0 * 0.1 / 44100.0;
private double z1;
private double z2;
@Override
public void generate(int start, int limit) {
double[] frequencies = frequency.getValues();
double[] amplitudes = amplitude.getValues();
double[] outputs = output.getValues();
// Variables have a single value.
double currentPhase = phase.getValue();
for (int i = start; i < limit; i++) {
/* Generate raw sawtooth phaser. */
double phaseIncrement = convertFrequencyToPhaseIncrement(frequencies[i]);
currentPhase = incrementWrapPhase(currentPhase, phaseIncrement);
/* Square the raw sawtooth. */
double squared = currentPhase * currentPhase;
// Differentiate using a delayed value.
double diffed = squared - z2;
z2 = z1;
z1 = squared;
/* Calculate scaling based on phaseIncrement */
double pinc = phaseIncrement;
// Absolute value.
if (pinc < 0.0) {
pinc = 0.0 - pinc;
}
double dpw;
// If the frequency is very low then just use the raw sawtooth.
// This avoids divide by zero problems and scaling problems.
if (pinc < VERY_LOW_FREQUENCY) {
dpw = currentPhase;
} else {
dpw = diffed * 0.25 / pinc;
}
outputs[i] = amplitudes[i] * dpw;
}
// Value needs to be saved for next time.
phase.setValue(currentPhase);
}
}
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