A single frequency tone, recorded at the head of a tape and used for alignment purposes when the tape is replayed at a later date.
"My husband was AMAZED when he opened his present to find his high school quartet on a CD!!! He thought it was truly UNIQUE!! I was very happy with the restoration. These recordings were made in someone's basement almost 50 years ago & sound so clear. (I was not even sure that your company would be able to GET any music off of them!!) Thank you ..."