OnAudioFilterRead generate sinewave

SineWave.cs

// https://forum.unity.com/threads/onaudiofilterread-question.170273/#post-1164846
using UnityEngine;
using System; // Needed for Math

public class SineWave : MonoBehaviour
{
  // un-optimized version
    public double frequency = 440;
    public double gain = 0.05;
    private double increment;
    private double phase;
    private double sampling_frequency = 48000;

    private double[] tones = { 440.0f, 1046.5f, 3729.3f, 1046.5f };
    private int tone_index;
    private float last_time;

    void Start()
    {
Debug.Log("" + tone_index + ": " + tones[tone_index]);     
    }

    void Update()
    {
        if (Time.realtimeSinceStartup - last_time > 1)
        {
            last_time = Time.realtimeSinceStartup;
            tone_index++;
            if (tone_index >= tones.Length)
                tone_index = 0;
Debug.Log("" + tone_index + ": " + tones[tone_index]);
        }
    }

    void OnAudioFilterRead(float[] data, int channels)
    {
// update increment in case frequency has changed
        increment = tones[tone_index] * 2 * Math.PI / sampling_frequency;

        for (var i = 0; i < data.Length; i += channels)
        {
            phase += increment;
// this is where we copy audio data to make them “available” to Unity
            data[i] = (float) (gain * Math.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 * Math.PI)
                phase = 0;
        }
    }
}