Divisi

In musical terminology, Divisi is an instruction to divide a single section of instruments into multiple subsections of instruments. This usually applies to the violins of the string section in an orchestra, although violas, celli, and contrabasses can also be divided.

References

Unison

In music, unison is two or more musical parts sounding the same pitch or at an octave interval, usually at the same time.

Rhythmic patterns which are homorhythmic are also called unison.

Interval of the unison

Unison or perfect unison (also called a prime, or perfect prime) may refer to the (pseudo-)interval formed by a tone and its duplication (in German, Unisono, Einklang, or Prime), for example C–C, as differentiated from the second, C–D, etc. In the unison the two pitches have the ratio of 1:1 or 0 half steps and zero cents. Although two tones in unison are considered to be the same pitch, they are still perceivable as coming from separate sources, whether played on instruments of a different type:  play unison on C, piano and guitar ; or of the same type:  play unison on C, two pianos . This is because a pair of tones in unison come from different locations and/or can have different "colors" (timbres), i.e. come from different musical instruments or human voices. Voices with different colors have, as sound waves, different waveforms. These waveforms have the same fundamental frequency but differ in the amplitudes of their higher harmonics. The unison is considered the most consonant interval while the near unison is considered the most dissonant. The unison is also the easiest interval to tune. The unison is abbreviated as P1.