Basic Chorus Operation - Source Audio Gemini Chorus User Manual

Basic Chorus Operation

When multiple musicians perform the same music in unison, their performances will always differ in
small ways – each individual musician's timing, pitch, and intensity will not exactly match the other
musicians, creating an overall sound that can be subjectively fuller or deeper than that of a single
musician. This result is commonly called chorusing.
The chorus effect attempts to recreate the sounds of multiple musicians playing in unison with only a
single instrument as an input. For example, a chorused guitar should, ideally, take one guitar and
make it sound like several guitars playing the same thing at the same time.
This effect is accomplished by creating copies of the input signal that differ slightly in timing, pitch,
amplitude, and (when in stereo mode) location in the stereo field.
As far as audio effects go, the chorus effect is very old. As early as the 1940s, analog delay circuits
with very short delay times were used in the Hammond organ to create a primitive chorus sound.
The Gemini uses multi-tap digital delay lines with modulated timing, amplitude modulation, panning,
and a few other tricks and techniques to create its wide array of chorus sounds.
The amount of delay in the chorus effect needs to be changed over time to create a convincing
representation of multiple voices. In order to do this, a low frequency oscillator (also known as an
LFO) is used to control the delay time, as well as several other parameters. This is illustrated by the
following graph:
TIME
The blue line in the graph is known as the LFO. It changes the amount of delay over time.
The frequency (a.k.a. "rate" or "speed") of the LFO can be increased to get a more rapid change in
the delay time, as shown in this graph:
SA242 Gemini Chorus User's Guide 9