Unison mode is described as multiplying the signal that is being created by the oscillator. This means that multiple notes will be playing the same pitch at the same time, or pitches spread across different octaves. In essence, it makes your sound fuller in a quick and simple process.
Many synths offer a Unison Detuning mode, this allows you to make very subtle changes to the pitch of each of the unison signals. After all of the signals have been slightly altered to various pitches, you will notice a much thicker sound due to the wider range of frequencies being used.
The most common number of unison options are 2, 4 or 8 voices, although there are some synthesizers out there that can offer more with advanced features, such as panning separate signals left and right and detuning them against a middle signal creating a huge stereo sound.
Unison vs Chorus
It is useful to know that Unison is not actually an effect, but rather a fixed option within your synth.
You may have realized that the Chorus function is capable of creating similar sounds. The main difference here is that the Chorus is an effect and simulates the multiple voices, whereas Unison mode is a process of actually creating and using multiple voices, it’s a lot simpler and creates less hassle when you are looking to beef up your sounds. You can go from plain and simple melodies to a huge sounding lead in just a few steps.