monostep/Source/dsp/WaveTables.h

#pragma once

#include <cmath>
#include <algorithm>
#include <random>

namespace monostep
{

enum class Waveform : int
{
    sine = 0,
    triangle = 1,
    saw = 2,
    square = 3,
    pulse = 4,
    noise = 5,
    sub = 6,
    pluck = 7
};

inline float frac (float x)
{
    return x - std::floor (x);
}

inline float polyBlep (float t, float dt)
{
    if (t < dt)
    {
        t /= dt;
        return t + t - t * t - 1.0f;
    }

    if (t > 1.0f - dt)
    {
        t = (t - 1.0f) / dt;
        return t * t + t + t + 1.0f;
    }

    return 0.0f;
}

inline float renderWave (Waveform w, float phase, float inc)
{
    switch (w)
    {
        case Waveform::sine:
            return std::sin (phase * 6.283185307179586f);

        case Waveform::triangle:
        {
            const float f = frac (phase);
            return 4.0f * std::min (f, 1.0f - f) - 1.0f;
        }

        case Waveform::saw:
        {
            const float f = frac (phase);
            return (2.0f * f - 1.0f) - polyBlep (f, inc);
        }

        case Waveform::square:
        {
            const float f = frac (phase);
            float v = (f < 0.5f) ? 1.0f : -1.0f;
            v += polyBlep (f, inc);
            v -= polyBlep (frac (f + 0.5f), inc);
            return v;
        }

        case Waveform::pulse:
        {
            const float f = frac (phase);
            return (f < 0.3f) ? 1.0f : -1.0f;
        }

        case Waveform::sub:
        {
            const float f = frac (phase * 0.25f);
            return 4.0f * std::min (f, 1.0f - f) - 1.0f;
        }

        case Waveform::noise:
        {
            thread_local static std::mt19937 rng { std::random_device {}() };
            thread_local static std::uniform_real_distribution<float> dist (-1.0f, 1.0f);
            return dist (rng);
        }

        case Waveform::pluck:
        {
            const float f = frac (phase);
            return 2.0f * std::sin (f * 6.283185307179586f * 2.0f) * std::exp (-10.0f * f);
        }
    }

    return 0.0f;
}

} // namespace monostep