Oscillator.cs

// based on YouTube tutorial by Dano Kablamo:
// https://youtu.be/GqHFGMy_51c
// https://www.reddit.com/r/Unity3D/comments/5lwwpn/i_made_this_tutorial_showing_you_how_to_get_nes/

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class Oscillator : MonoBehaviour {

    public double frequency = 440.0; // freq in hz
    private double increment; //
    private double phase; // location on wave
    private double sampling_frequency = 48000.0; // 48k

    // volume/power of audio
    public float gain;
    public float volume = 0.1f;

    public float[] frequencies;
    public int thisFreq;

    void Start() {
        frequencies = new float[8];
        frequencies[0] = 440;
        frequencies[1] = 494;
        frequencies[2] = 554;
        frequencies[3] = 587;
        frequencies[4] = 659;
        frequencies[5] = 740;
        frequencies[6] = 831;
        frequencies[7] = 880;
    }

    void Update() {
        if (Input.GetKeyDown(KeyCode.Space)) {
            gain = volume;
            frequency = frequencies[thisFreq];
            thisFreq++;
            thisFreq = thisFreq % frequencies.Length;
        }

        if (Input.GetKeyUp(KeyCode.Space)) {
            gain = 0;
        }
    }

    private void OnAudioFilterRead(float[] data, int channels) {
        increment = frequency * 2.0 * Mathf.PI / sampling_frequency;

        for (int i = 0; i < data.Length; i += channels) {
            phase += increment;
            data[i] = 0;
            /*
            //Sin
            data[i] += (float)(gain * Mathf.Sin((float)(phase)));
            /**/

            //Square
            if (gain * Mathf.Sin((float)phase) >= 0 * gain) {
                data[i] += (float)gain * 0.6f;
            } else {
                data[i] += (float)gain * -0.6f;
            }
            /**/
            /*
            // Triangle
            data[i] += (float)(gain * (double)Mathf.PingPong((float)phase, 1.0f));
            /**/

            //data[i] = data[i] / 3;

            if (channels == 2) {
                data[i + 1] = data[i];
            }

            if (phase > Mathf.PI * 2) {
                phase = 0.0;
            }
        }
    }
}