1 /*
2  * Copyright (C) 2015 The Android Open Source Project
3  *
4  * Licensed under the Apache License, Version 2.0 (the "License");
5  * you may not use this file except in compliance with the License.
6  * You may obtain a copy of the License at
7  *
8  *      http://www.apache.org/licenses/LICENSE-2.0
9  *
10  * Unless required by applicable law or agreed to in writing, software
11  * distributed under the License is distributed on an "AS IS" BASIS,
12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13  * See the License for the specific language governing permissions and
14  * limitations under the License.
15  */
16 
17 package com.example.android.common.midi.synth;
18 
19 /**
20  * Band limited sawtooth oscillator.
21  * This will have very little aliasing at high frequencies.
22  */
23 public class SawOscillatorDPW extends SawOscillator {
24     private float mZ1 = 0.0f; // delayed values
25     private float mZ2 = 0.0f;
26     private float mScaler; // frequency dependent scaler
27     private final static float VERY_LOW_FREQ = 0.0000001f;
28 
29     @Override
setFrequency(float freq)30     public void setFrequency(float freq) {
31         /* Calculate scaling based on frequency. */
32         freq = Math.abs(freq);
33         super.setFrequency(freq);
34         if (freq < VERY_LOW_FREQ) {
35             mScaler = (float) (0.125 * 44100 / VERY_LOW_FREQ);
36         } else {
37             mScaler = (float) (0.125 * 44100 / freq);
38         }
39     }
40 
41     @Override
render()42     public float render() {
43         float phase = incrementWrapPhase();
44         /* Square the raw sawtooth. */
45         float squared = phase * phase;
46         float diffed = squared - mZ2;
47         mZ2 = mZ1;
48         mZ1 = squared;
49         return diffed * mScaler * getAmplitude();
50     }
51 
52 }
53