(Lü), an acoustic system upon which Chinese music is founded. It is based on a 12-pitch chromatic scale, taken within the range of an octave; the scale is constructed by means of 12 bamboo tubes pitched according to the fifth-fourth principle. The liu originated in ancient times and was perfected and refined over the centuries. Selecting certain steps of the scale, Chinese musicians developed various pentatonic modes that are characteristic of folk and professional Chinese music.