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1 /*
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2 * FeedbackOscillator.cpp
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3 *
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4 * Recursive phase-shift oscillator implemented
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5 * on the matrix
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6 *
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7 * Andrew McPherson 2014
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8 */
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9
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10 #include "FeedbackOscillator.h"
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11 #include <cstdlib>
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12 #include <cmath>
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13
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14 #define COEFF_B0 0
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15 #define COEFF_B1 1
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16 #define COEFF_A1 2
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17
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18 FeedbackOscillator::FeedbackOscillator()
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19 : wavetable1(0), wavetable2(0)
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20 {
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21
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22 }
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23
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24 FeedbackOscillator::~FeedbackOscillator() {
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25 if(wavetable1 != 0)
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26 free(wavetable1);
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27 if(wavetable2 != 0)
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28 free(wavetable2);
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29
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30 }
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31
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32 // Initialise the settings for the feedback oscillator
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33 void FeedbackOscillator::initialise(int maxTableSize, float hpfCutoffFrequency, float matrixSampleRate) {
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34 wavetableMaxLength = maxTableSize;
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35 if(wavetable1 != 0)
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36 free(wavetable1);
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37 if(wavetable2 != 0)
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38 free(wavetable2);
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39
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40 wavetable1 = (float *)malloc(maxTableSize * sizeof(float));
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41 wavetable2 = (float *)malloc(maxTableSize * sizeof(float));
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42
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43 float omega = tan(M_PI * hpfCutoffFrequency / matrixSampleRate);
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44 float n = 1.0f / (1.0f + omega);
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45
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46 coeffs[COEFF_A1] = (omega - 1.0f) * n;
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47 coeffs[COEFF_B0] = n;
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48 coeffs[COEFF_B1] = -n;
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49
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50 for(int n = 0; n < maxTableSize; n++)
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51 wavetable1[n] = wavetable2[n] = 0;
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52
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53 wavetableRead = wavetable1;
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54 wavetableWrite = wavetable2;
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55 wavetableWritePointer = 0;
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56 sampleCount = lastTriggerCount = 0;
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57 }
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58
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59 // Process one sample and store the output value
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60 // Returns true if the wavetable needs rendering
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61 int FeedbackOscillator::process(float input, float *output) {
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62 float outFloat = coeffs[COEFF_B0] * input + coeffs[COEFF_B1] * lastInput - coeffs[COEFF_A1] * lastOutput;
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63 int requestRenderLength = 0;
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64
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65 if(outFloat < -0.5)
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66 *output = 0;
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67 else if(outFloat > 0.5)
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68 *output = 1;
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69 else
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70 *output = outFloat + 0.5;
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71
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72 if(canTrigger && outFloat > 0 && lastOutput <= 0) {
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73 triggered = true;
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74 requestRenderLength = wavetableWritePointer; // How many samples stored thus far?
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75 if(requestRenderLength < 4)
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76 requestRenderLength = 0; // Ignore anything with fewer than 4 points
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77
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78 lastTriggerCount = sampleCount;
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79 canTrigger = false;
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80 wavetableWritePointer = 0;
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81
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82 // Swap buffers
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83 float *temp = wavetableWrite;
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84 wavetableWrite = wavetableRead;
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85 wavetableRead = temp;
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86 }
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87
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88 if(triggered) {
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89 wavetableWrite[wavetableWritePointer] = outFloat;
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90 if(++wavetableWritePointer >= wavetableMaxLength) {
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91 triggered = false;
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92 wavetableWritePointer = 0;
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93 }
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94 }
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95
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96 if(sampleCount - lastTriggerCount > 40)
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97 canTrigger = true;
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98
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99 sampleCount++;
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100
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101 lastOutput = outFloat;
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102 lastInput = input;
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103
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104 return requestRenderLength;
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105 }
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