// FADEOUT
	public IEnumerator FadeOut(AudioSource audioSource, float duration)
    {
        float startVolume = audioSource.volume;

        float time = 0f;
        while (time < duration)
        {
            time += Time.deltaTime;
            audioSource.volume = Mathf.Lerp(startVolume, 0f, time / duration);
            yield return null;
        }

        audioSource.volume = 0f;
        audioSource.Stop();
    }

// FADEIN
public IEnumerator FadeIn(AudioSource audioSource, float duration, float targetVolume = 1f)
{
    float time = 0f;
    audioSource.volume = 0f;
    audioSource.Play();

    while (time < duration)
    {
        time += Time.deltaTime;
        audioSource.volume = Mathf.Lerp(0f, targetVolume, time / duration);
        yield return null;
    }

    audioSource.volume = targetVolume;
}