unison
theoryYOO-nih-sun
Two or more voices or instruments performing the same note or melody simultaneously.
Unison means all together on the same note — two or more voices or instruments performing the same pitch simultaneously. In orchestral contexts, unison can also refer to performers playing the same melody at octave intervals, which is called octave unison.
Unison passages create a powerful, focused sound. An entire string section playing in unison produces a rich, unified tone that is both louder and more complex than a single instrument. Composers use unison for moments of particular strength or simplicity — the opening of Beethoven's Fifth Symphony is essentially a unison statement. Unison singing in choirs creates a primal, commanding effect.
When a full symphony orchestra plays in unison, the slight variations between 80+ instruments create a complex, shimmering sound that is richer than any single instrument could produce.