Procedural Audio in Unity - Noise and Tone

Procedural audio is audio that is created using code at run time, rather than using a wav or mp3 sound file. It can be very useful for creating audio that reacts to the situation and does not sound repetitive, which is difficult with prerecorded sound files.

To use the following script, create a GameObject in Unity and add an AudioSource. Add the following C# script to the GameObject. The script will automatically add a AudioLowPassFilter to the GameObject.

Press play and listen to the procedural audio! You can mess around with the public variables on this script. Frequency is set to 330Hz (an A tone) but change this to change the pitch. The amount of noise compared to the tone volume is set by noiseRatio. You can change the sound of the noise using the settings on the AudioLowPassFilter

//By Benjamin Outram
//C# script for use in Unity 

// create a new file and copy paste this.  Name the file:
// ProceduralAudio.cs
// attach script to a GameObject that has an AudioSource on it.
// adjust the public variables to experiment.

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

[RequireComponent(typeof(AudioLowPassFilter))]
public class ProceduralAudio : MonoBehaviour
{
    private float sampling_frequency = 48000;

    [Range(0f, 1f)]
    public float noiseRatio = 0.5f;

    //for noise part
    [Range(-1f, 1f)]
    public float offset;

    public float cutoffOn = 800;
    public float cutoffOff = 100;

    public bool cutOff;


    //for tonal part

    public float frequency = 440f;
    public float gain = 0.05f;

    private float increment;
    private float phase;

    System.Random rand = new System.Random();
    AudioLowPassFilter lowPassFilter;

    void Awake()
    {
        sampling_frequency = AudioSettings.outputSampleRate;

        lowPassFilter = GetComponent<AudioLowPassFilter>();
        Update();
    }

    void OnAudioFilterRead(float[] data, int channels)
    {
        float tonalPart = 0;
        float noisePart = 0;

        // update increment in case frequency has changed
        increment = frequency * 2f * Mathf.PI / sampling_frequency;

        for (int i = 0; i < data.Length; i++)
        {

            //noise
            noisePart = noiseRatio * (float)(rand.NextDouble() * 2.0 - 1.0 + offset);

            phase = phase + increment;
            if (phase > 2 * Mathf.PI) phase = 0;

            //tone
            tonalPart = (1f - noiseRatio) * (float)(gain * Mathf.Sin(phase));

            //together
            data[i] = noisePart + tonalPart;

            // if we have stereo, we copy the mono data to each channel
            if (channels == 2)
            {
                data[i + 1] = data[i];
                i++;
            }


        }




    }

    void Update()
    {
        lowPassFilter.cutoffFrequency = cutOff ? cutoffOn : cutoffOff;
    }



}

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