
(from the article `keyboard instrument`) ...1 13 feet) above the unison. These are used melodically to colour the unison and octave stops, and they may be wide or narrow in scale. Such stops ... Each rank of pipes, such as the diapason, is controlled by a separate stop. Mutation stops consist of pipes sounding higher (e.g., by five note...
Found on
http://www.britannica.com/eb/a-z/m/145

A mutation stop is an organ pipe sounding the harmonic of the note normally produced.
Found on
http://www.probertencyclopaedia.com/browse/VM.HTM
No exact match found.