AudioSource.pitch

Description

The pitch of the audio source.

Pitch is a quality that makes a melody go higher or lower. As an example imagine playing an audio clip with pitch set to one. Increasing the pitch as the clip plays will make the clip sound like it is higher. Similarly decreasing the pitch less than one makes the clip sound lower.

//Attach this script to a GameObject.
//Attach an AudioSource to your GameObject (Click Add Component and go to Audio>Audio Source). Choose an audio clip in the AudioClip field.
//This script sets the pitch of the audio at the start, and then gradually turns it down to 0 as time passes.

using UnityEngine;

//Make sure there is an Audio Source component on the GameObject
[RequireComponent(typeof(AudioSource))]

public class ExampleScript : MonoBehaviour
{
    public int startingPitch = 4;
    public int timeToDecrease = 5;
    AudioSource audioSource;

    void Start()
    {
        //Fetch the AudioSource from the GameObject
        audioSource = GetComponent<AudioSource>();

        //Initialize the pitch
        audioSource.pitch = startingPitch;
    }

    void Update()
    {
        //While the pitch is over 0, decrease it as time passes.
        if (audioSource.pitch > 0)
        {
            audioSource.pitch -= Time.deltaTime * startingPitch / timeToDecrease;
        }
    }
}

Another example:

using UnityEngine;

// A script that plays your chosen song.  The pitch starts at 1.0.
// You can increase and decrease the pitch and hear the change
// that is made.

public class AudioExample : MonoBehaviour
{
    public float pitchValue = 1.0f;
    public AudioClip mySong;

    private AudioSource audioSource;
    private float low = 0.75f;
    private float high = 1.25f;

    void Awake()
    {
        audioSource = GetComponent<AudioSource>();
        audioSource.clip = mySong;
        audioSource.loop = true;
    }

    void OnGUI()
    {
        pitchValue = GUI.HorizontalSlider(new Rect(25, 75, 100, 30), pitchValue, low, high);
        audioSource.pitch = pitchValue;
    }
}