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1 /* -*- c-basic-offset: 4 indent-tabs-mode: nil -*- vi:set ts=8 sts=4 sw=4: */
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2
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3 /*
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4 Sonic Visualiser
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5 An audio file viewer and annotation editor.
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6 Centre for Digital Music, Queen Mary, University of London.
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7 This file copyright 2006 Chris Cannam.
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8
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9 This program is free software; you can redistribute it and/or
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10 modify it under the terms of the GNU General Public License as
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11 published by the Free Software Foundation; either version 2 of the
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12 License, or (at your option) any later version. See the file
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13 COPYING included with this distribution for more information.
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14 */
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15
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16 #include "LogRange.h"
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17 #include "system/System.h"
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18
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19 #include <algorithm>
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20 #include <iostream>
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21 #include <cmath>
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22
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23 void
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24 LogRange::mapRange(float &min, float &max, float logthresh)
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25 {
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26 if (min > max) std::swap(min, max);
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27 if (max == min) max = min + 1;
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28
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29 // DEBUG << "LogRange::mapRange: min = " << min << ", max = " << max << endl;
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30
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31 if (min >= 0.f) {
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32
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33 max = log10f(max); // we know max != 0
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34
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35 if (min == 0.f) min = std::min(logthresh, max);
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36 else min = log10f(min);
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37
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38 // DEBUG << "LogRange::mapRange: positive: min = " << min << ", max = " << max << endl;
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39
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40 } else if (max <= 0.f) {
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41
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42 min = log10f(-min); // we know min != 0
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43
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44 if (max == 0.f) max = std::min(logthresh, min);
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45 else max = log10f(-max);
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46
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47 std::swap(min, max);
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48
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49 // DEBUG << "LogRange::mapRange: negative: min = " << min << ", max = " << max << endl;
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50
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51 } else {
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52
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53 // min < 0 and max > 0
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54
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55 max = log10f(std::max(max, -min));
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56 min = std::min(logthresh, max);
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57
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58 // DEBUG << "LogRange::mapRange: spanning: min = " << min << ", max = " << max << endl;
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59 }
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60
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61 if (min == max) min = max - 1;
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62 }
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63
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64 float
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65 LogRange::map(float value, float thresh)
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66 {
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67 if (value == 0.f) return thresh;
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68 return log10f(fabsf(value));
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69 }
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70
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71 float
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72 LogRange::unmap(float value)
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73 {
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74 return powf(10.0, value);
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75 }
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76
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77 static float
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78 sd(const std::vector<float> &values, size_t start, size_t n)
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79 {
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80 float sum = 0.f, mean = 0.f, variance = 0.f;
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81 for (size_t i = 0; i < n; ++i) {
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82 sum += values[start + i];
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83 }
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84 mean = sum / n;
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85 for (size_t i = 0; i < n; ++i) {
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86 float diff = values[start + i] - mean;
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87 variance += diff * diff;
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88 }
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89 variance = variance / n;
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90 return sqrtf(variance);
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91 }
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92
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93 bool
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94 LogRange::useLogScale(std::vector<float> values)
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95 {
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96 // Principle: Partition the data into two sets around the median;
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97 // calculate the standard deviation of each set; if the two SDs
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98 // are very different, it's likely that a log scale would be good.
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99
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100 if (values.size() < 4) return false;
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101 std::sort(values.begin(), values.end());
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102 size_t mi = values.size() / 2;
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103
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104 float sd0 = sd(values, 0, mi);
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105 float sd1 = sd(values, mi, values.size() - mi);
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106
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107 DEBUG << "LogRange::useLogScale: sd0 = "
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108 << sd0 << ", sd1 = " << sd1 << endl;
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109
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110 if (sd0 == 0 || sd1 == 0) return false;
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111
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112 // I wonder what method of determining "one sd much bigger than
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113 // the other" would be appropriate here...
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114 if (std::max(sd0, sd1) / std::min(sd0, sd1) > 10.f) return true;
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115 else return false;
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116 }
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117
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