The Chorus phenomenon


Chorus effect occurs when several individual sounds with similar pitch and timbre play in unison. This phenomenon occurs naturally with a group of singers or violinists, who will always exhibit slight variations with pitch and timing, even when playing in unison. These slight variations are crucial for producing the lush and shimmering sound we are accustomed to hearing from large choirs or string sections. The chorus audio effect simulates these pitch and timing variations, making a single instrument source sound as if there were several instruments playing together.


Chorus origins

Origin of the chorus effect can be traced back to the 1930`s with the use of the Hammond organ instruments. This was actually the first time that one signal was out of tune on purpose and therefore the physical detuning is created. Later on in the 1960`s ADT (Automatic Double Tracking) effect was first used by some professional recording studios. This effect used a copy of a recording, which was slightly delayed and played over the original signal. The first use of this effect and the reason why it became widely popular was in 1966 when The Beatles requested it for their recording in Abbey Road Studios.

In the following years, various combinations between synthesizers and organs had the similar approach in order to create chorus type of sound.  The classic chorus sound that we know today was widely popularized by the appearance of now-famous Boss-CE 1, which was first presented in mid-1970`s as a first stand-alone chorus pedal. This device left a mark on countless records of that time and continued to be immensely used in the decades to follow.




Chorus can be considered as common guitar pedal effect that gives a clean electric guitar a “dreamy” quality. It’s also widely used on the acoustic guitar, electric piano, and clavinet. Furthermore, on strings and synth pads, chorus creates a richer, more complex sound. Stereo chorus effects also can be used to widen a stereo image.


Modern-day Chorus

Nowadays we have a large number of chorus effects in both analog and digital realm with many variations. The principal controls of modern chorus software effects include parameters such as LFO speed (a.k.a. rate or period) and depth (a.k.a. amplitude or intensity). LFO speeds are usually in the range of natural human vibrato (up to about 10 Hertz). In addition, some plugins include control of the wet/dry mix. At 100% wet, the pitch modulation of a chorus effect sounds like vibrato. To blend the modulated audio with the original, the wet/dry mix is often set at 50% of each.

Most common variations of chorus effect are :

– Mono, Stereo or Surround chorus
– Single and Multi-voice chorus
– More advanced types of chorus effects with complex LFO`s

Additional Resources & Source Texts