ardupilot/libraries/AP_HAL_SITL/Synth.hpp

// See https://github.com/OneLoneCoder/synth

#ifndef SYNTH_HPP
#define SYNTH_HPP

////////////////////////////////////////////////////////////
// Headers
////////////////////////////////////////////////////////////
#include <SFML/Audio.hpp>
#include <cmath>

namespace Synth
{
enum eWaveType { OSC_SINE, OSC_SQUARE, OSC_TRIANGLE, OSC_SAW_ANA, OSC_SAW_DIG, OSC_NOISE };

struct sEnvelope
{
    double dAttackTime = 0.0;
    double dDecayTime = 0.0;
    double dSustainTime = 1.0;
    double dReleaseTime = 0.0;
    double dStartAmplitude = 1.0;
    double dSustainAmplitude = 1.0;
};
struct sTone
{
    eWaveType waveType = OSC_SINE;
    double dStartFrequency = 440.0;
    double dEndFrequency = 440.0;
    double dAmplitude = 1.0;
};
    
////////////////////////////////////////////////////////////
// Converts frequency (Hz) to angular velocity
////////////////////////////////////////////////////////////
const double PI = 3.14159265359;
double w(const double dHertz)
{
    return dHertz * 2.0 * PI;
}


////////////////////////////////////////////////////////////
// Multi-Function Oscillator
//
// This function was mostly "borrowed" from One Lone Coder blog at
// wwww.onelonecoder.com
//
////////////////////////////////////////////////////////////
double osc(double dHertz, double dTime, eWaveType waveType)
{
    switch (waveType)
    {
    case OSC_SINE: // Sine wave bewteen -1 and +1
        return sin(w(dHertz) * dTime);

    case OSC_SQUARE: // Square wave between -1 and +1
        return sin(w(dHertz) * dTime) > 0 ? 1.0 : -1.0;

    case OSC_TRIANGLE: // Triangle wave between -1 and +1
        return asin(sin(w(dHertz) * dTime)) * (2.0 / PI);

    case OSC_SAW_ANA: // Saw wave (analogue / warm / slow)
    {
        double dOutput = 0.0;
        // this variable defines warmth, larger the number harsher and more similar do OSC_SAW_DIG sound becomes
        double dWarmth = 30.0;

        for (double n = 1.0; n < dWarmth; n++)
            dOutput += (sin(n * w(dHertz) * dTime)) / n;

        return dOutput * (2.0 / PI);
    }

    case OSC_SAW_DIG: // Saw Wave (optimised / harsh / fast)
        return (2.0 / PI) * (dHertz * PI * fmod(dTime, 1.0 / dHertz) - (PI / 2.0));

    case OSC_NOISE: // Pseudorandom noise
        return 2.0 * ((double)rand() / (double)RAND_MAX) - 1.0;

    default:
        return 0.0;
    }
}

////////////////////////////////////////////////////////////
// Amplitude Modulator
////////////////////////////////////////////////////////////
double amplitude(double dTime, sEnvelope env)
{
    // double dTimeOn = 0;
    double dTimeOff = env.dAttackTime + env.dDecayTime + env.dSustainTime;
    double dAmplitude = 0.0;

    if (dTime > dTimeOff)                                                                                                                  // Release phase
        dAmplitude = ((dTime - dTimeOff) / env.dReleaseTime) * (0.0 - env.dSustainAmplitude) + env.dSustainAmplitude;

    else if (dTime > (env.dAttackTime + env.dDecayTime))                                                                                   // Sustain phase
        dAmplitude = env.dSustainAmplitude;

    else if (dTime > env.dAttackTime && dTime <= (env.dAttackTime + env.dDecayTime))                                                       // Decay phase
        dAmplitude = ((dTime - env.dAttackTime) / env.dDecayTime) * (env.dSustainAmplitude - env.dStartAmplitude) + env.dStartAmplitude;

    else if (dTime <= env.dAttackTime)                                                                                                     // Attack phase
        dAmplitude = (dTime / env.dAttackTime) * env.dStartAmplitude;

    // Amplitude should not be negative, check just in case
    if (dAmplitude <= 0.000)
        dAmplitude = 0.0;

    return dAmplitude;
}



////////////////////////////////////////////////////////////
/// \brief Generate sound and store in SoundBuffer
///
/// This function uses case-in
///
/// \param buffer is address to SoundBuffer where the result will be stored
/// \param envelope structure defining the ADSR Envelope
/// \param tones vector of tone structures to be stacked
/// \param master volume for the volume of sound
/// \param sample rate to set quality of sound
///
/// \return True if the sound was generate, false if it failed
///
////////////////////////////////////////////////////////////
bool generate(sf::SoundBuffer* buffer, sEnvelope env, std::vector<sTone> tones, unsigned uMasterVol, unsigned uSampleRate)
{
    if (!buffer)
        return false;

    // Calculate and allocate buffer
    double dTotalDuration = env.dAttackTime + env.dDecayTime + env.dSustainTime + env.dReleaseTime;
    unsigned iBufferSize = unsigned(dTotalDuration * uSampleRate);
    sf::Int16 * iRaw;
    iRaw = new sf::Int16[iBufferSize];

    // Generate sound
    double dIncrement = 1.0 / double(uSampleRate);
    double dTime = 0.0;
    for (unsigned i = 0; i < iBufferSize; i++)
    {
        double signal = 0.0;
            
        // Generate multiple tones and stack them together
        for (sTone t : tones)
        {
            double dFrequency = t.dStartFrequency + ((t.dEndFrequency - t.dStartFrequency) * (double(i) / double(iBufferSize)));
            signal = signal + (osc(dFrequency, dTime, t.waveType) * t.dAmplitude);
        }

        // Calculate Amplitude based on ADSR envelope
        double dEnvelopeAmplitude = amplitude(dTime, env);

        // Apply master volume, envelope and store to buffer
        *(iRaw + i) = sf::Int16(uMasterVol * signal * dEnvelopeAmplitude);

        dTime += dIncrement;
    }

	// Load into SFML SoundBuffer
    bool bSuccess = buffer->loadFromSamples(iRaw, iBufferSize, 1, uSampleRate);
    delete[] iRaw;

    return bSuccess;
}

////////////////////////////////////////////////////////////
/// \brief Generate sound and store in SoundBuffer
///
/// This function uses case-in
///
/// \param buffer is address to SoundBuffer where the result will be stored
/// \param envelope structure defining the ADSR Envelope
/// \param tone structure for simple tone definition
/// \param master volume for the volume of sound
/// \param sample rate to set quality of sound
///
/// \return True if the sound was generate, false if it failed
///
////////////////////////////////////////////////////////////
bool generate(sf::SoundBuffer* buffer, sEnvelope env, sTone tone, unsigned uMasterVol, unsigned uSampleRate)
{
    std::vector<sTone> tones;
    tones.push_back(tone);
    return generate(buffer, env, tones, uMasterVol, uSampleRate);
}
}
#endif  // SYNTH_HPP