I have the CD, and do listen to it on the way to the lake sometimes. It helps to refresh your memory a bit, when starting out the season. Another valuable tip that I gained from it, is attaching a couple different targets to your water shoes as a sound check, for when your ears get fatigued. I used gorilla glue to adhere a dime on one water shoe, and a nickle on the other. You will be surprised how far off your hearing can get through out the day. Deeper targets also start sounding different.
(I have found a few targets that were good, when they had the exact signature as a bottle cap.)
Not very often though. Usually the other way around.- Sounds good at first, then it works in that warble sound as you are rechecking the hole while trying to recover the target.
Note: The SUN RAY shoes are the best thing I ever bought for water detecting. These are going on the 3rd season, and still are very good condition. All the cheap water shoes wear the bottoms off right away, and fall apart. I can scruff the gravel/rock bottom, and not tear the rubber off. We have a lot of broken glass and sharp objects in our lakes, so I feel it is absolutely a must to have a well built water shoe for protection and comfort! I think I paid around $60-$70 for these- Worth EVERY penny!