The holes in a wind instrument or the key which blocks them.Also, the registers of an organ or the mechanism that activates them.A device that alters the tone color of a harpsichord or clavichord by adding or deleting strings, by the damping (or undamping) of all or selected strings.Modifying the pitch of a brass instrument (normally the horn) by insterting the hand into the bell.a lever on a harpsichord or organ that controls the use of pipes or strings. To 'stop' a string on a string instrument is to place a fingertip on it, which causes it to vibrate more quickly, and raises its pitch. To stop a horn is to place a hand firmly inside the bell to give a different sound quality.