10 #include "pitchdetector.h"
12 PitchDetector::PitchDetector(unsigned sample_rate, unsigned fft_length, unsigned pad_factor, unsigned overlap)
13 : sample_rate(sample_rate), fft_length(fft_length), pad_factor(pad_factor), overlap(overlap)
15 in = reinterpret_cast<double *> (fftw_malloc(sizeof(double) * fft_length / pad_factor));
16 in_windowed = reinterpret_cast<double *> (fftw_malloc(sizeof(double) * fft_length));
17 out = reinterpret_cast<std::complex<double> *> (fftw_malloc(sizeof(std::complex<double>) * (fft_length / 2 + 1)));
18 bins = reinterpret_cast<double *> (fftw_malloc(sizeof(double) * (fft_length / 2 + 1)));
20 memset(in, 0, sizeof(double) * fft_length / pad_factor);
22 plan = fftw_plan_dft_r2c_1d(fft_length, in_windowed, reinterpret_cast<fftw_complex *> (out), FFTW_ESTIMATE);
24 // Initialize the Hamming window
25 window_data = new double[fft_length / pad_factor];
26 for (unsigned i = 0; i < fft_length / pad_factor; ++i) {
27 window_data[i] = 0.54 - 0.46 * cos(2.0 * M_PI * double(i) / double(fft_length/pad_factor - 1));
31 PitchDetector::~PitchDetector()
34 fftw_free(in_windowed);
39 std::pair<double, double> PitchDetector::detect_pitch(short *buf)
41 unsigned buf_len = fft_length / pad_factor / overlap;
42 memmove(in, in + buf_len, (fft_length / pad_factor - buf_len) * sizeof(double));
44 for (unsigned i = 0; i < buf_len; ++i)
45 in[i + (fft_length / pad_factor - buf_len)] = double(buf[i]);
47 apply_window(in, in_windowed, fft_length);
49 find_peak_magnitudes(out, bins, fft_length);
50 std::pair<double, double> peak = find_peak(bins, fft_length);
52 peak = adjust_for_overtones(peak, bins, fft_length);
57 // Apply a standard Hamming window to our input data.
58 void PitchDetector::apply_window(double *in, double *out, unsigned num_samples)
60 for (unsigned i = 0; i < num_samples / pad_factor; ++i) {
61 out[i] = in[i] * window_data[i];
63 for (unsigned i = num_samples / pad_factor; i < num_samples; ++i) {
68 void PitchDetector::find_peak_magnitudes(std::complex<double> *in, double *out, unsigned num_samples)
70 for (unsigned i = 0; i < num_samples / 2 + 1; ++i)
74 std::pair<double, double> PitchDetector::find_peak(double *in, unsigned num_samples)
76 double best_peak = in[5];
77 unsigned best_bin = 5;
79 for (unsigned i = 6; i < num_samples / 2 + 1; ++i) {
80 if (in[i] > best_peak) {
85 if (20.0 * log10(in[i] / fft_length) > 0.0) {
86 printf("PEAK: %+4.2f dB %5.2f Hz\n",
87 20.0 * log10(in[i] / fft_length),
88 bin_to_freq(i, num_samples));
93 if (best_bin == 0 || best_bin == num_samples / 2) {
94 return std::make_pair(-1.0, 0.0);
98 printf("undertone strength: %+4.2f %+4.2f %+4.2f [%+4.2f] %+4.2f %+4.2f %+4.2f\n",
99 20.0 * log10(in[best_bin*4] / fft_length),
100 20.0 * log10(in[best_bin*3] / fft_length),
101 20.0 * log10(in[best_bin*2] / fft_length),
102 20.0 * log10(in[best_bin] / fft_length),
103 20.0 * log10(in[best_bin/2] / fft_length),
104 20.0 * log10(in[best_bin/3] / fft_length),
105 20.0 * log10(in[best_bin/4] / fft_length));
108 // see if we might have hit an overtone (set a limit of 10dB)
109 for (unsigned i = 6; i >= 1; --i) {
110 if (best_bin != best_bin / i &&
111 20.0 * log10(in[best_bin] / in[best_bin / i]) < 10.0f &&
114 printf("Overtone of degree %u!\n", i);
118 // consider sliding one bin up or down
119 if (best_bin > 1 && in[best_bin - 1] > in[best_bin] && in[best_bin - 1] > in[best_bin - 2]) {
121 } else if (best_bin < num_samples / 2 - 1 && in[best_bin + 1] > in[best_bin] && in[best_bin + 1] > in[best_bin + 2]) {
129 if (best_bin == 0 || best_bin == num_samples / 2) {
130 return std::make_pair(-1.0, 0.0);
132 std::pair<double, double> peak =
133 interpolate_peak(in[best_bin - 1],
137 return std::make_pair(bin_to_freq(double(best_bin) + peak.first, num_samples), peak.second);
140 // it's perhaps not ideal to _first_ find the peak and _then_ the harmonics --
141 // ideally, one should find the set of all peaks and then determine the likely
142 // base from that... something for later. :-)
143 std::pair<double, double> PitchDetector::adjust_for_overtones(std::pair<double, double> base, double *in, unsigned num_samples)
145 double mu = base.first, var = 1.0 / (base.second * base.second);
147 //printf("Base at %.2f (amp=%5.2fdB)\n", base.first, base.second);
149 for (unsigned i = 2; i < 10; ++i) {
150 unsigned middle = unsigned(floor(freq_to_bin(base.first, num_samples) * i + 0.5));
151 unsigned lower = middle - (i+1)/2, upper = middle + (i+1)/2;
155 if (upper >= num_samples)
156 upper = num_samples - 2;
158 // printf("Searching in [%u,%u] = %f..%f\n", lower, upper, bin_to_freq(lower, num_samples), bin_to_freq(upper, num_samples));
160 // search for a peak in this interval
161 double best_harmonics_freq = -1.0;
162 double best_harmonics_amp = -1.0;
163 for (unsigned j = lower; j <= upper; ++j) {
164 if (in[j] > in[j-1] && in[j] > in[j+1]) {
165 std::pair<double, double> peak =
166 interpolate_peak(in[j - 1],
170 if (peak.second > best_harmonics_amp) {
171 best_harmonics_freq = bin_to_freq(j + peak.first, num_samples);
172 best_harmonics_amp = peak.second;
177 if (best_harmonics_amp <= 0.0)
180 //printf("Found overtone %u at %.2f (amp=%5.2fdB)\n", i, best_harmonics_freq,
181 // best_harmonics_amp);
183 double this_mu = best_harmonics_freq / double(i);
184 double this_var = 1.0 / (best_harmonics_amp * best_harmonics_amp);
186 double k = var / (var + this_var);
187 mu = (1.0 - k) * mu + k * this_mu;
190 return std::make_pair(mu, base.second);
193 double PitchDetector::bin_to_freq(double bin, unsigned num_samples)
195 return bin * sample_rate / double(num_samples);
197 double PitchDetector::freq_to_bin(double freq, unsigned num_samples)
199 return freq * double(num_samples) / double(sample_rate);
203 * Given three bins, find the interpolated real peak based
204 * on their magnitudes. To do this, we execute the following
207 * Fit a polynomial of the form ax^2 + bx + c = 0 to the data
208 * we have. Maple readily yields our coefficients, assuming
209 * that we have the values at x=-1, x=0 and x=1:
211 * > f := x -> a*x^2 + b*x + c;
214 * f := x -> a x + b x + c
216 * > cf := solve({ f(-1) = ym1, f(0) = y0, f(1) = y1 }, { a, b, c });
219 * cf := {c = y0, b = ---- - ---, a = ---- + --- - y0}
222 * Now let's find the maximum point for the polynomial (it has to be
223 * a maximum, since y0 is the greatest value):
225 * > xmax := solve(subs(cf, diff(f(x), x)) = 0, x);
228 * xmax := -------------------
229 * 2 (y1 + ym1 - 2 y0)
231 * We could go further and insert {fmax,a,b,c} into the original
232 * polynomial, but it just gets hairy. We calculate a, b and c separately
235 * http://www-ccrma.stanford.edu/~jos/parshl/Peak_Detection_Steps_3.html
236 * claims that detection is almost twice as good when using dB scale instead
237 * of linear scale for the input values, so we use that. (As a tiny bonus,
238 * we get back dB scale from the function.)
240 std::pair<double, double> PitchDetector::interpolate_peak(double ym1, double y0, double y1)
251 double a = 0.5 * y1 + 0.5 * ym1 - y0;
252 double b = 0.5 * y1 - 0.5 * ym1;
255 double xmax = (ym1 - y1) / (2.0 * (y1 + ym1 - 2.0 * y0));
256 double ymax = 20.0 * (a * xmax * xmax + b * xmax + c) - 70.0;
258 return std::make_pair(xmax, ymax);