Unison is when several instruments or voices play the same melody at the same pitch, or the same melody an octave apart. It is used when you want the melody to sound thicker, stronger and more striking. Layering different timbres, such as voice and guitar or strings and brass, still works as unison.
What unison achieves
Doubling the same phrase gives a stronger outline than a single instrument and lets you highlight the important parts of a song. Having several people sing the chorus melody, or layering a lead synth with guitar, are standard ways to raise the energy.
How it differs from harmony
Unison layers the same melody, while harmony sounds different pitches together to create thickness. Making the lead line clear with unison first and then adding notes above or below as needed produces thickness that stays organized.
Octave unison
Rather than exactly the same pitch, playing the same melody an octave above or below is also common. The lower note adds weight and the higher one adds brightness and cut, so you can widen the range while emphasizing the lead line.
Building it in your DAW
You can try it simply by duplicating the melody’s MIDI and sending it to a different sound. But layering too many similar timbres in the same range can muddy the sound or just raise the level. Vary the octave, the timbre and the note timing slightly, and compare the single part with the layered version.
How it differs from the synth function called unison
Unison on a synthesizer can mean a function that stacks several voices on one note to thicken it. This page covers unison in the musical and performance sense. For the synth function, see Unison (synthesizer function).
