X-Git-Url: https://git.sesse.net/?p=pitch;a=blobdiff_plain;f=pitchdetector.cpp;fp=pitchdetector.cpp;h=71e5875c7b328a31a38ba45540d967c861af316f;hp=0000000000000000000000000000000000000000;hb=66156de8eb723c104b616223f8ca7cc20ea55d05;hpb=cbf0d7c43e3aa06886d425c4d26c99592eb35ba6 diff --git a/pitchdetector.cpp b/pitchdetector.cpp new file mode 100644 index 0000000..71e5875 --- /dev/null +++ b/pitchdetector.cpp @@ -0,0 +1,251 @@ +#include +#include +#include +#include +#include +#include +#include +#include +#include "pitchdetector.h" + +PitchDetector::PitchDetector(unsigned sample_rate, unsigned fft_length, unsigned pad_factor, unsigned overlap) + : sample_rate(sample_rate), fft_length(fft_length), pad_factor(pad_factor), overlap(overlap) +{ + in = reinterpret_cast (fftw_malloc(sizeof(double) * fft_length / pad_factor)); + in_windowed = reinterpret_cast (fftw_malloc(sizeof(double) * fft_length)); + out = reinterpret_cast *> (fftw_malloc(sizeof(std::complex) * (fft_length / 2 + 1))); + bins = reinterpret_cast (fftw_malloc(sizeof(double) * (fft_length / 2 + 1))); + + memset(in, 0, sizeof(double) * fft_length / pad_factor); + + plan = fftw_plan_dft_r2c_1d(fft_length, in_windowed, reinterpret_cast (out), FFTW_ESTIMATE); + + // Initialize the Hamming window + window_data = new double[fft_length / pad_factor]; + for (unsigned i = 0; i < fft_length / pad_factor; ++i) { + window_data[i] = 0.54 - 0.46 * cos(2.0 * M_PI * double(i) / double(fft_length/pad_factor - 1)); + } +} + +PitchDetector::~PitchDetector() +{ + fftw_free(in); + fftw_free(in_windowed); + fftw_free(out); + fftw_free(bins); +} + +std::pair PitchDetector::detect_pitch(short *buf) +{ + unsigned buf_len = fft_length / pad_factor / overlap; + memmove(in, in + buf_len, (fft_length - buf_len) * sizeof(double)); + + for (unsigned i = 0; i < buf_len; ++i) + in[i + (fft_length / pad_factor - buf_len)] = double(buf[i]); + + apply_window(in, in_windowed, fft_length); + fftw_execute(plan); + find_peak_magnitudes(out, bins, fft_length); + std::pair peak = find_peak(bins, fft_length); + if (peak.first > 0.0) + peak = adjust_for_overtones(peak, bins, fft_length); + + return peak; +} + +// Apply a standard Hamming window to our input data. +void PitchDetector::apply_window(double *in, double *out, unsigned num_samples) +{ + for (unsigned i = 0; i < num_samples / pad_factor; ++i) { + out[i] = in[i] * window_data[i]; + } + for (unsigned i = num_samples / pad_factor; i < num_samples; ++i) { + out[i] = 0.0; + } +} + +void PitchDetector::find_peak_magnitudes(std::complex *in, double *out, unsigned num_samples) +{ + for (unsigned i = 0; i < num_samples / 2 + 1; ++i) + out[i] = abs(in[i]); +} + +std::pair PitchDetector::find_peak(double *in, unsigned num_samples) +{ + double best_peak = in[5]; + unsigned best_bin = 5; + + for (unsigned i = 6; i < num_samples / 2 + 1; ++i) { + if (in[i] > best_peak) { + best_peak = in[i]; + best_bin = i; + } + } + + if (best_bin == 0 || best_bin == num_samples / 2) { + return std::make_pair(-1.0, 0.0); + } + +#if 0 + printf("undertone strength: %+4.2f %+4.2f %+4.2f [%+4.2f] %+4.2f %+4.2f %+4.2f\n", + 20.0 * log10(in[best_bin*4] / fft_length), + 20.0 * log10(in[best_bin*3] / fft_length), + 20.0 * log10(in[best_bin*2] / fft_length), + 20.0 * log10(in[best_bin] / fft_length), + 20.0 * log10(in[best_bin/2] / fft_length), + 20.0 * log10(in[best_bin/3] / fft_length), + 20.0 * log10(in[best_bin/4] / fft_length)); +#endif + + // see if we might have hit an overtone (set a limit of 5dB) + for (unsigned i = 4; i >= 1; --i) { + if (best_bin != best_bin / i && + 20.0 * log10(in[best_bin] / in[best_bin / i]) < 5.0f) { +#if 0 + printf("Overtone of degree %u!\n", i); +#endif + best_bin /= i; + + // consider sliding one bin up or down + if (best_bin > 1 && in[best_bin - 1] > in[best_bin] && in[best_bin - 1] > in[best_bin - 2]) { + --best_bin; + } else if (best_bin < num_samples / 2 - 1 && in[best_bin + 1] > in[best_bin] && in[best_bin + 1] > in[best_bin + 2]) { + ++best_bin; + } + + break; + } + } + + if (best_bin == 0 || best_bin == num_samples / 2) { + return std::make_pair(-1.0, 0.0); + } + std::pair peak = + interpolate_peak(in[best_bin - 1], + in[best_bin], + in[best_bin + 1]); + + return std::make_pair(bin_to_freq(double(best_bin) + peak.first, num_samples), peak.second); +} + +// it's perhaps not ideal to _first_ find the peak and _then_ the harmonics -- +// ideally, one should find the set of all peaks and then determine the likely +// base from that... something for later. :-) +std::pair PitchDetector::adjust_for_overtones(std::pair base, double *in, unsigned num_samples) +{ + double mu = base.first, var = 1.0 / (base.second * base.second); + + //printf("Base at %.2f (amp=%5.2fdB)\n", base.first, base.second); + + for (unsigned i = 2; i < 10; ++i) { + unsigned middle = unsigned(floor(freq_to_bin(base.first, num_samples) * i + 0.5)); + unsigned lower = middle - (i+1)/2, upper = middle + (i+1)/2; + + if (lower < 1) + lower = 1; + if (upper >= num_samples) + upper = num_samples - 2; + + // printf("Searching in [%u,%u] = %f..%f\n", lower, upper, bin_to_freq(lower, num_samples), bin_to_freq(upper, num_samples)); + + // search for a peak in this interval + double best_harmonics_freq = -1.0; + double best_harmonics_amp = -1.0; + for (unsigned j = lower; j <= upper; ++j) { + if (in[j] > in[j-1] && in[j] > in[j+1]) { + std::pair peak = + interpolate_peak(in[j - 1], + in[j], + in[j + 1]); + + if (peak.second > best_harmonics_amp) { + best_harmonics_freq = bin_to_freq(j + peak.first, num_samples); + best_harmonics_amp = peak.second; + } + } + } + + if (best_harmonics_amp <= 0.0) + continue; + + //printf("Found overtone %u at %.2f (amp=%5.2fdB)\n", i, best_harmonics_freq, + // best_harmonics_amp); + + double this_mu = best_harmonics_freq / double(i); + double this_var = 1.0 / (best_harmonics_amp * best_harmonics_amp); + + double k = var / (var + this_var); + mu = (1.0 - k) * mu + k * this_mu; + var *= (1.0 - k); + } + return std::make_pair(mu, base.second); +} + +double PitchDetector::bin_to_freq(double bin, unsigned num_samples) +{ + return bin * sample_rate / double(num_samples); +} +double PitchDetector::freq_to_bin(double freq, unsigned num_samples) +{ + return freq * double(num_samples) / double(sample_rate); +} + +/* + * Given three bins, find the interpolated real peak based + * on their magnitudes. To do this, we execute the following + * plan: + * + * Fit a polynomial of the form ax^2 + bx + c = 0 to the data + * we have. Maple readily yields our coefficients, assuming + * that we have the values at x=-1, x=0 and x=1: + * + * > f := x -> a*x^2 + b*x + c; + * + * 2 + * f := x -> a x + b x + c + * + * > cf := solve({ f(-1) = ym1, f(0) = y0, f(1) = y1 }, { a, b, c }); + * + * y1 ym1 y1 ym1 + * cf := {c = y0, b = ---- - ---, a = ---- + --- - y0} + * 2 2 2 2 + * + * Now let's find the maximum point for the polynomial (it has to be + * a maximum, since y0 is the greatest value): + * + * > xmax := solve(subs(cf, diff(f(x), x)) = 0, x); + * + * -y1 + ym1 + * xmax := ------------------- + * 2 (y1 + ym1 - 2 y0) + * + * We could go further and insert {fmax,a,b,c} into the original + * polynomial, but it just gets hairy. We calculate a, b and c separately + * instead. + * + * http://www-ccrma.stanford.edu/~jos/parshl/Peak_Detection_Steps_3.html + * claims that detection is almost twice as good when using dB scale instead + * of linear scale for the input values, so we use that. (As a tiny bonus, + * we get back dB scale from the function.) + */ +std::pair PitchDetector::interpolate_peak(double ym1, double y0, double y1) +{ + ym1 = log10(ym1); + y0 = log10(y0); + y1 = log10(y1); + +#if 0 + assert(y0 >= y1); + assert(y0 >= ym1); +#endif + + double a = 0.5 * y1 + 0.5 * ym1 - y0; + double b = 0.5 * y1 - 0.5 * ym1; + double c = y0; + + double xmax = (ym1 - y1) / (2.0 * (y1 + ym1 - 2.0 * y0)); + double ymax = 20.0 * (a * xmax * xmax + b * xmax + c) - 90.0; + + return std::make_pair(xmax, ymax); +} +