(compass in music). In the earliest Church melodies, the compass did not in some instances reach, and in few did it exceed, a fifth. In Gregorian music the octave was the limit, but in later times this compass was much extended. A melody occupying or employing its whole compass was called cantus perfectus; falling short of this, cantus imperfectus; exceeding it, cantus plusquamperfectus. Subsequently other interpretations have been given to the word ambitus.