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/*
* Copyright (C) 2016 The Android Open Source Project
*
* 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.
*
* This code was translated from the JSyn Java code.
* JSyn is Copyright 2009 Phil Burk, Mobileer Inc
* JSyn is licensed under the Apache License, Version 2.0
*/
#ifndef SYNTHMARK_DIFFERENTIATED_PARABOLA_H
#define SYNTHMARK_DIFFERENTIATED_PARABOLA_H
#include <cstdint>
#include <math.h>
#include "SynthTools.h"
namespace marksynth {
constexpr double kDPWVeryLowFrequency = 2.0 * 0.1 / kSynthmarkSampleRate;
/**
* DPW is a tool for generating band-limited waveforms
* based on a paper by Antti Huovilainen and Vesa Valimaki:
* "New Approaches to Digital Subtractive Synthesis"
*/
class DifferentiatedParabola
{
public:
DifferentiatedParabola()
: mZ1(0)
, mZ2(0) {}
virtual ~DifferentiatedParabola() = default;
synth_float_t next(synth_float_t phase, synth_float_t phaseIncrement) {
synth_float_t dpw;
synth_float_t positivePhaseIncrement = (phaseIncrement < 0.0)
? phaseIncrement
: 0.0 - phaseIncrement;
// If the frequency is very low then just use the raw sawtooth.
// This avoids divide by zero problems and scaling problems.
if (positivePhaseIncrement < kDPWVeryLowFrequency) {
dpw = phase;
} else {
// Calculate the parabola.
synth_float_t squared = phase * phase;
// Differentiate using a delayed value.
synth_float_t diffed = squared - mZ2;
// Delay line.
// TODO - Why Z2. Vesa's paper says use Z1?
mZ2 = mZ1;
mZ1 = squared;
// Calculate scaling
dpw = diffed * 0.25f / positivePhaseIncrement; // TODO extract and optimize
}
return dpw;
}
private:
synth_float_t mZ1;
synth_float_t mZ2;
};
};
#endif // SYNTHMARK_DIFFERENTIATED_PARABOLA_H
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