yaw-audio/lib/scale/scale.h

#ifndef YAW_SCALE_INCLUDED
#define YAW_SCALE_INCLUDED

#include <vector>
#include <string>

static std::vector<std::string> defaultNoteNames = {
    "A",
    "A#",
    "B",
    "C",
    "C#",
    "D",
    "D#",
    "E",
    "F",
    "F#",
    "G",
    "G#"};

class Scale
{
    double sampleRate = 48000.0;

    // freqs in hz, periods in samples
    std::vector<double> frequencies;
    std::vector<double> periods;
    std::vector<std::string> names;

public:
    void newSampleRate(double rate)
    {
        double ratio = rate / sampleRate;
        sampleRate = rate;
        for (double &note : periods)
            note *= ratio;
    };

    // Default ctor: 12TET @ 48kHz
    Scale(double hz = 440.0)
    {
        hz /= 32.0;

        for (int oct = 0; oct < 8; ++oct)
        {
            
            for (int j = 0; j < 12; ++j)
            {
                double note = exp2(j / 12.0) * hz * (1 << oct);
                frequencies.push_back(note);
                periods.push_back(sampleRate / note);
                names.push_back(defaultNoteNames[j]);
            }
        }
    }

    double getNearestPeriod(double period)
    {
        for (auto note : periods)
        {
            if (period > note)
                return note;
        }

        // This should NOT happen.
        return 0;
    }

    double getNearestNoteNumber(double hz)
    {
        for (unsigned int i = 0; i < frequencies.size(); ++i)
        {
            if (hz < frequencies[i])
            {
                if (i == 0)
                    return i;
                return 1.0 * i + (hz - frequencies[i - 1]) / (frequencies[i] - frequencies[i - 1]);
            }
        }

        return 0.0;
    }

    double getNearestFrequency(double hz)
    {
        for (auto note : frequencies)
        {
            if (hz < note)
                return note;
        }

        return 0;
    }

    // TODO: parse scala files. new ctor that parses arbitrary scales
};

#endif