Reduce AudioClip when a key is pressed.

Hi guys.
I would like to reduce “Motore2” when I press Key A, and reduce “Motore1” when I press Key “D”. How can I add this?

using UnityEngine;
using System.Collections;

public class Audio : MonoBehaviour
{
	public AudioClip Motore1;
	public AudioClip Motore2;
	float soundPitch = 0;
	float maxSpeed = 2;
	float minSpeed = 0.2f;


	
	void Start()
	{
		if (!audio.playOnAwake) audio.Play();
	}
	
	
	// Update is called once per frame
	void Update () 
	{
		soundPitch = Mathf.Clamp(soundPitch, minSpeed, maxSpeed);


		if (Input.GetKey(KeyCode.A)) 
		{
			audio.clip = Motore1;
			soundPitch+= 0.09f;
			audio.pitch = (soundPitch);

		}



		if (Input.GetKey (KeyCode.D)) 
		{
			audio.clip = Motore2;
			soundPitch+= 0.09f;
			audio.pitch = (soundPitch);
		}


		if (Input.GetKey (KeyCode.S)) 
		{
			soundPitch-= 0.09f;
			audio.pitch = (soundPitch);
		}

	}


}

If you want to have multiple sounds playing at once, you need to have multiple GameObjects/AudioSources that you manage separately.