如何将音符名称和频率存储为数据以在 java 中的其他类中使用

Question

I want to build some sort of array that will store the note names eg A4 and it's frequency eg 440 I also want to know what sort of class I should use to do this.

I want to be able to use a wave generator class to generate that note as a waveform like a Sine or square wave. Example

public SineGenerator(double amplitude, Note note, int bitRate, double duration) {

SineGenerator sg = new SineGenerator(0.8, C4(or middle C, 261.63Hz), 16, 1);

The Note class will index C4 in some sort of array and then return Middle C's frequency, 261.63 to the SineGenerator and SineGenerator will generate the sine wave.

Answer 1

For storing the note names and their respective frequency, look up HashMaps, it sounds like what you're looking for. Use the note names as Key and the frequencies as Value.

HashMap<String, Double> Notes = new HashMap<>();

Answer 2

If I understood correctly, you are asking for a rough guide of how to implement the Note class.

The Note class will probably contain 3 main fields:

private char letter;
private int octave;
private boolean sharp;

A note such as D♭ ₄ will have a letter of C , octave of 4 and a sharp of true . As you can see, I am representing D♭ and C# as the same note here, as they have the same frequency, and the only thing of importance here seems to be the frequency.

Note will also have a HashMap<String, Double> or HashMap<String, Integer> to store the frequency of each note. Note that you don't need to store the semitones in this map, as you can just multiply the note below by 1.0595 (or Math.pow(2, 1.0 / 12) ) to get the semitone frequency.

And then you'd write a method called getFrequency , which accesses the map. If sharp is true, multiply it by 1.0595 and return.

Here's a simple implementation that I have written:

class Note {
    private char letter;
    private int octave;
    private boolean sharp;

    private static HashMap<String, Integer> map;

    static {
        map = new HashMap<>();
        map.put("C0", 16);
        map.put("D0", 18);
        map.put("E0", 21);
        map.put("F0", 22);
        map.put("G0", 25);
        map.put("A1", 28);
        // ...
    }

    public Note(char letter, int octave, boolean sharp) {
        this.letter = letter;
        this.octave = octave;
        this.sharp = sharp;
    }

    public char getLetter() {
        return letter;
    }

    public int getOctave() {
        return octave;
    }

    public boolean isSharp() {
        return sharp;
    }

    public double getFrequency() {
        String key = Character.toString(letter) + octave;
        double frequency = map.get(key);
        if (sharp) {
            frequency *= Math.pow(2, 1.0 / 12);
        }
        return frequency;
    }
}