If you want to become a professional singer or if you are already a professional singer, you can improve your voice even more with a singing training cd.  A lot of people put music in their CD players.  You can put a training tape in yours and listen whenever you have time.  You can even listen to your CD player when your in bed.  This is a great time to learn, because you are more relaxed.  If you fall asleep at night listening to the vocal training lessons, it will not be long before you start to truly see a difference in your overall performance. Give it a try.  You will find that is well worth the effort.