In music theory, harmonic rhythm, also known as harmonic tempo, is the rate at which the chords change in a musical composition, in relation to the rate of notes. Thus a passage in common time with a stream of sixteenth notes and chord changes every measure has a slow harmonic rhythm and a fast surface or "musical" rhythm, while a piece with a trickle of half notes and chord changes twice a measure has a fast harmonic rhythm and a slow surface rhythm. Harmonic rhythm may be described as strong or weak.