private void PlaySound()
{
if (isAccelerating == 1) {
//slowly turn on engine sound
audioSource.volume = Mathf.Lerp(audioSource.volume, 1, 0.1f);
}
else {
//slowly turn off engine sound
audioSource.volume = Mathf.Lerp(audioSource.volume, 0, 0.1f);
}
if (!audioSource.isPlaying) {
audioSource.Play ();
}
}