UnityでProcedual Audio

Sineus.cs

/*
 * refs
 * http://tips.hecomi.com/entry/2014/11/11/021147
 * http://d.hatena.ne.jp/nakamura001/20120724/1343148980
 * https://gist.github.com/keijiro/3806478
 * https://codepen.io/DavidSabine/pen/kyAlJ
 * https://femurdesign.com/theremin/
 */

using UnityEngine;
using UnityEngine.UI;

[RequireComponent(typeof(AudioSource))]
public class Sinus : MonoBehaviour
{
    const float PI2 = Mathf.PI * 2;
    const float PI_2 = Mathf.PI / 2.0f;
    public Text toggle;
    [Range(55, 1760)]
    public float frequency = 440;
    public float gain = 0.4f;
    private float increment;
    private float phase;
    private float sampling_frequency = 44100;
    private bool playing = false;
    private AudioSource audio_;

    void Awake()
    {

        // オーディオ出力設定、44100 Hz がデフォルト
        sampling_frequency = AudioSettings.outputSampleRate;

        audio_ = GetComponent<AudioSource>();
        audio_.clip = AudioClip.Create("(null)", 44100, 1, 44100, true, (data) => { });
        audio_.loop = true;
    }

    /// <summary>
    /// If OnAudioFilterRead is implemented, Unity will insert a custom filter into the
    /// audio DSP chain.
    /// </summary>
    /// <param name="data">An array of floats comprising the audio data.</param>
    /// <param name="channels">An int that stores the number of channels
    ///                        of audio data passed to this delegate.</param>
    void SineWave(float[] data, int channels)
    {
        // update increment in case frequency has changed
        increment = frequency * 2 * Mathf.PI / sampling_frequency;
        for (var i = 0; i < data.Length; i += channels)
        {
            phase += increment;
            data[i] = gain * Mathf.Sin(phase);
            // if we have stereo, we copy the mono data to each channel
            if (channels == 2)
            {
                data[i + 1] = data[i];
            }
            if (phase > 2 * Mathf.PI)
            {
                phase = 0;
            }
        }
    }

    void SquareWave(float[] data, int channels)
    {
        increment = frequency * 2 * Mathf.PI / sampling_frequency;
        for (var i = 0; i < data.Length; i = i + channels)
        {
            phase += increment;

            data[i] = (float)(gain * ((phase % PI2) < PI2 * 0.5 ? 1.0 : -1.0));
            if (channels == 2)
            {
                data[i + 1] = data[i];
            }
            if (phase > 2 * Mathf.PI)
            {
                phase = 0;
            }
        }
    }

    void OnAudioFilterRead(float[] data, int channels)
    {
        if (!playing)
        {
            return;
        }
        SineWave(data, channels);
    }

    public void TogglePlay()
    {
        if (playing)
        {
            audio_.Stop();
            toggle.text = "Play";
        }
        else
        {
            audio_.Play();
            toggle.text = "Stop";
        }
        playing = !playing;
    }

    public void SetFrequency(float f)
    {
        frequency = f;
    }
}