Like the music of Asia, India and the Middle East, it is a highly rhythmic music. African music consists of complex rhythmic patterns, often involving one rhythm played against another to create a polyrhythm. The most common polyrhythm plays three beats on top of two, like a triplet played against straight notes. Beyond the rhythmic nature of the music, African music differs from Western music in that the various parts of the music do not necessarily combine in a harmonious fashion. African musicians unlike Western musicians, do not seek to combine different sounds in a way that is pleasing to the ear. Instead their aim is to express life, in all its aspects, through the medium of sound. Each instrument or part may represent a particular aspect of life, or a different character; the through-line of each instrument/part matters more than how the different instruments and parts fit together. Understanding African music gets even more difficult when you consider that it does not have a written tradition; there is little or no written music to study or analyze. This makes it almost impossible to notate the music – especially the melodies and harmonies – using the Western staff. There are subtle differences in pitch and intonation that do not easily translate to Western notation. That said, African music most closely adheres to Western tetratonic (three-notes), pentatonic (five-note), hexatonic (six-note), and heptatonic (seven-note) scales. Harmonization of the melody is accomplished by singing in parallel thirds, fourths, or fifths. Another distinguishing form of African music is its call-and-response nature: one voice or instrument plays a short melodic phrase, and that phrase is echoed by another voice or instrument. The call-and-response nature extends to the rhythm, where one drum will play a rhythmic pattern, echoed by another drum playing the same pattern. African music is also highly improvised. (This speaks to the lack of a written tradition. ) A core rhythmic pattern is typically played, with drummers then improvising new patterns over the static original patterns.