Machinegun Sound (automatic gunfire) synthesis in Unity3D

MachinegunSound.cs

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

// @kurtdekker - synthesizes a cheesy machinegun sound
//
// DO NOT PUT THIS IN ANY SCENE!!!!
//
// Instead, simply use it by calling:
//
//		MachinegunSound.Instance.SetRunning( true or false);
//
// That's it. You may call that every frame if you like.
//
// Be sure to turn off your gun in your OnDisable()
//
// I use this code in my Pilot Kurt game:
//
// Appstore: https://apps.apple.com/us/app/pilot-kurt/id1153921946
// GooglePlay: https://play.google.com/store/apps/details?id=com.plbm.flight1
// Android TV: https://play.google.com/store/apps/details?id=com.plbm.flight1tv

public class MachinegunSound : MonoBehaviour
{
	private static MachinegunSound _Instance;
	public static MachinegunSound Instance
	{
		get
		{
			if (!_Instance)
			{
				_Instance = new GameObject().AddComponent<MachinegunSound>();
				_Instance.name = _Instance.GetType().ToString();
			}
			return _Instance;
		}
	}

	bool running;
	float volume;

	public void SetRunning( bool _running)
	{
		running = _running;

		// TODO: read your volume from your own sound volume settings here
		volume = 1.0f;

		// bring it down a bit
		volume = volume / 4;

		if (volume == 0)
		{
			running = false;
		}
	}

	void Awake()
	{
		// fabricate a noise lookup table
		int NoiseTableCount = 20000;
		noiseTable = new float[NoiseTableCount];
		for (int i = 0; i < noiseTable.Length; i++)
		{
			noiseTable[i] = Random.value;
		}

		var source = gameObject.AddComponent<AudioSource>();
		source.bypassListenerEffects = true;
	}

	int noiseRover;
	float[] noiseTable;

	// how frequently do we rerun the envelope? (samples)
	const int envelopeRate = 100;
	int envelopeRover;
	float[] envelope = new float[] {
		1.0f,
		1.0f,
		1.0f,
		1.0f,
		0.8f,
		0.8f,
		0.7f,
		0.6f,
		0.5f,
		0.4f,
		0.3f,
		0.2f,
		0.1f,
		0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
	};

	void OnAudioFilterRead(float[] data, int channels)
	{
		if (!running)
		{
			envelopeRover = 0;
			return;
		}

		int dataLen = data.Length / channels;

		int n = 0;
		while (n < dataLen)
		{
			float x = noiseTable[noiseRover];

			x *= envelope[envelopeRover / envelopeRate];

			x *= volume;

			noiseRover++;
			if (noiseRover >= noiseTable.Length)
			{
				noiseRover = 0;
			}

			envelopeRover++;
			if (envelopeRover >= envelope.Length * envelopeRate)
			{
				envelopeRover = 0;
			}

			int channel = 0;
			while (channel < channels)
			{
				data[n * channels + channel] = x;
				channel++;
			}

			n++;
		}
	}
}

MachinegunTester.cs

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

// @kurtdekker - used to test MachinegunSound.cs
// To use:
//	- drop this script on an empty GameObject
//	- press and hold G when you want guns.

public class MachinegunTester : MonoBehaviour
{
	void Start ()
	{
		Debug.Log( "Press/Hold the G key to fire guns");	
	}
	
	void Update ()
	{
		bool onoff = Input.GetKey( KeyCode.G);

		MachinegunSound.Instance.SetRunning( onoff);
	}
}