Wavetable generator

generate.cpp

#include "kiss_fftr.h"
#include <memory>
#include <complex>

static std::complex<kiss_fft_scalar> make_bin(double amplitude, double phase = 0.0)
{
    return std::polar<kiss_fft_scalar>(0.5 * amplitude, phase + M_PI / 2);
}

static void make_sine(kiss_fft_scalar *wave, int size, double amplitude)
{
    typedef std::complex<kiss_fft_scalar> cpx;

    std::unique_ptr<cpx[]> spec{new cpx[size / 2 + 1]{}};
    spec[1] = make_bin(amplitude);

    kiss_fftr_cfg cfg = kiss_fftr_alloc(size, true, nullptr, nullptr);
    kiss_fftri(cfg, reinterpret_cast<kiss_fft_cpx *>(spec.get()), wave);
    kiss_fftr_free(cfg);
}

static void make_triangle(kiss_fft_scalar *wave, int size, double amplitude)
{
    typedef std::complex<kiss_fft_scalar> cpx;

    std::unique_ptr<cpx[]> spec{new cpx[size / 2 + 1]{}};
    for (int i = 1, s = 0; i < size / 2 + 1; i += 2, s = !s) {
        spec[i] = make_bin(
            amplitude * (8 / (M_PI * M_PI)) * (1.0 / (i * i)),
            s ? 0.0 : M_PI);
    }

    kiss_fftr_cfg cfg = kiss_fftr_alloc(size, true, nullptr, nullptr);
    kiss_fftri(cfg, reinterpret_cast<kiss_fft_cpx *>(spec.get()), wave);
    kiss_fftr_free(cfg);
}

static void make_saw(kiss_fft_scalar *wave, int size, double amplitude)
{
    typedef std::complex<kiss_fft_scalar> cpx;

    std::unique_ptr<cpx[]> spec{new cpx[size / 2 + 1]{}};
    for (int i = 1; i < size / 2 + 1; ++i) {
        spec[i] = make_bin(
            amplitude * (2.0 / M_PI) / i,
            (i & 1) ? 0.0 : M_PI);
    }

    kiss_fftr_cfg cfg = kiss_fftr_alloc(size, true, nullptr, nullptr);
    kiss_fftri(cfg, reinterpret_cast<kiss_fft_cpx *>(spec.get()), wave);
    kiss_fftr_free(cfg);
}

static void make_square(kiss_fft_scalar *wave, int size, double amplitude)
{
    typedef std::complex<kiss_fft_scalar> cpx;

    std::unique_ptr<cpx[]> spec{new cpx[size / 2 + 1]{}};
    for (int i = 1; i < size / 2 + 1; i += 2)
        spec[i] = make_bin(amplitude * (4.0 / M_PI) / i, M_PI);

    kiss_fftr_cfg cfg = kiss_fftr_alloc(size, true, nullptr, nullptr);
    kiss_fftri(cfg, reinterpret_cast<kiss_fft_cpx *>(spec.get()), wave);
    kiss_fftr_free(cfg);
}

#include <cstdio>

int main(int argc, char *argv[])
{
    int waveno = 0;
    float amplitude = 1.0;
    int size = 256;

    if (argc > 1)
        waveno = std::stoi(argv[1]);
    if (argc > 2)
        amplitude = std::stof(argv[2]);
    if (argc > 3)
        size = std::stoi(argv[3]);

    float *wave = new float[size];

    switch (waveno) {
    default: case 0:
        make_sine(wave, size, amplitude);
        break;
    case 1:
        make_triangle(wave, size, amplitude);
        break;
    case 2:
        make_saw(wave, size, amplitude);
        break;
    case 3:
        make_square(wave, size, amplitude);
        break;
    }

    for (int i = 0; i < size; ++i)
        printf("%d %e\n", i, wave[i]);

    delete[] wave;

    return 0;
}