Concept
Chorus (or chorusing, choruser or chorused effect) is an audio effect that occurs when individual sounds with approximately the same time, and very similar pitches, converge. While similar sounds coming from multiple sources can occur naturally, as in the case of a choir or string orchestra, it can also be simulated using an electronic effects unit or signal processing device. When the effect is produced successfully, none of the constituent sounds are perceived as being out of tune. It is characteristic of sounds with a rich, shimmering quality that would be absent if the sound came from a single source. The shimmer occurs because of beating. The effect is more apparent when listening to sounds that sustain for longer periods of time. The chorus effect is especially easy to hear when listening to a choir or string ensemble. A choir has multiple people singing each part (alto, tenor, etc.). A string ensemble has multiple violinists and possibly multiples of other stringed instruments. Although most acoustic instruments cannot produce a chorus effect by themselves, some instruments (particularly, chordophones with multiple courses of strings) can produce it as part of their own design. The effect can make these acoustic instruments sound fuller and louder than by using a single tone generator (b.e.: a single vibrating string or a reed). Some examples: Piano – Each of the hammers strikes a course of multiple strings tuned to nearly the same pitch (for all notes except the bass notes). Professional piano tuners carefully control the mistuning of each string to add movement without losing clarity. However, in some poorly-cared instruments (like the honky-tonk pianos), the effect is more prominent. Santur (and similar coursed-hammered dulcimers) – As well as on the piano, the player can strike (by using a pair of manual hammers instead) a course of multiple strings tuned to nearly the same pitch. As the instrument is frequently tuned by the musicians themselves (rather than by professional tuners), the chorus effect is more easily heard than on the piano.