Chorus (sound engineering)

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The chorus is an effect that characterizes a tone as if a second, similar tone were simultaneously sounding and moving in the room.

It can be produced in terms of sound by an effects device or it can occur automatically, for example in plucked instruments whose strings are stretched in unisonous pairs (upper pairs of strings in bouzouki , 12-string guitar, etc.), as well as in the piano , whose hammers strike three strings at the same time , or with bagpipes and organ , when several similar pipes sound together. The effect can also be heard in a well-rehearsed choir - where it gets its name from.


If two sound sources have exactly the same pitch at the same time, there is no chorus effect; a mere copy of the original source is not enough. Only when the pitch of the copy deviates a little from the original does the impression of doubling and beating arise . Therefore, in the above examples, the strings and voices are deliberately slightly out of tune within their groups, but only so minimally that the listener does not perceive the detuning as wrong.

According to this detuning principle, a natural echo can also produce a chorus effect, provided that the original sound source or the echo varies the pitch over time in such a way that the two sound sources, i.e. the original and the echo, are slightly apart from each other at the time the echo occurs have different pitches. In the case of an echo, gusts of wind can vary the pitch. Such modulation is only referred to in a broad sense as chorus; in a narrow sense, chorus is an effect without an audible echo.

Sudden noises are not very suitable for a chorus effect; This is only clearly audible for tones that are voiced and last at least a quarter of a second.

Technical implementation


Similar to the flanger , the chorus creates a time-shifted duplicate of the sound source to be processed; the chorus delays this by about 15 milliseconds. This delayed duplicate is mixed with the original. The delay can be created using software in audio programs as well as with digital or analog electronics, as well as with analog tape technology. In contrast to the flanger, which uses shorter delay times, the phase cancellations and increases in the chorus are only weak, that is, the typical "jet-like" sound colorations of the flanger ( comb filter effects) are less noticeable in the chorus. However, the delay in the chorus is still so short that the listener does not recognize an echo, but perceives the original and the duplicate as being at the same time (the human echo threshold is above around 25 milliseconds).


The delay time of the mixed signal is alternately shortened, lengthened, shortened, lengthened, and so on. This process is called modulation. During the shortening, the wavelengths also become shorter, that is, the mixed tone becomes higher. During the extension it gets deeper. This creates the desired slight detuning between the delayed and original signal.

The modulation of the time delay can be represented graphically as a wave, such as a sine or triangle wave. Wave graphics can usually also be found on the labels of the chorus devices, but these usually do not describe the course of the time delay, but rather that of the resulting pitch. For example, with the Boss CE-1 Chorus Ensemble from the Japanese company Roland, a square wave form is specified, i.e. the tone is alternately steadily high and steadily low. This is generated by means of a triangular wave in the time delay modulation. If the delay time is continuously shortened, the tone remains constantly high; with constant extension it is always low; and without changing the time, the pitch remains original. This principle is identical to the Doppler effect .

The component responsible for modulation is called the LFO ( Low Frequency Oscillator ). Some chorus models have more than one LFO. For example, with a slow LFO superimposed by a second, faster LFO, a more turbulent, more intricate modulation curve can be created.

Stereo option

Many chorus models offer the option of reproducing the floating effect in stereo. Either several independently modulated chorus signals are distributed in the stereo panorama ; or, if only one chorus signal is available, this is mixed in equally loudly on the left and right, but on one side with reversed phase .

Problems in the bass range

With bass frequencies, a delay time of 15 milliseconds can lead to undesirably strong phase cancellations. Half a wave phase of 15 milliseconds in duration corresponds to a frequency of 33 Hertz over the entire phase length, i.e. a fundamental tone that is important for bass instruments. This, and according to the modulation also the adjacent tones, are canceled by the chorus. To avoid this, there are special chorus models for bass guitars; In this case, only the higher frequency spectrum of the chorus is processed by means of a high pass , the lower one remains untreated.

Flanger and Chorus

Chorus as a floor effect device

The main difference to the flanger is that the chorus aims more at doubling the voices than at coloring the timbre ; with the flanger this weighting is reversed. The flanger also has a feedback function that can send the delayed signal back into the effect input; the chorus does not have this function.

Other techniques

Furthermore, a chorus-like effect can also be created with a slightly detuned pitch shifter .

Construction and controls

Chorus effects can be created with software and hardware. In hardware, the chorus is usually available as part of multi-effects devices in 19-inch housings, or as a floor-effect device with a foot switch.

In the form of a floor effect device, the controls are usually simple and offer the following basic parameters (the general English names in brackets):

  • Speed ​​of the LFO, about 0.1 to 10 Hertz ( speed or rate )
  • Amount of detuning, including depth or width called ( depth or width )
  • Volume ratio between the original and delayed signal ( mix or dry / wet )

More complex models have additional parameters:

  • Basic delay time ( delay )
  • Volume of the original signal can be reduced to zero, for vibrato without a chorus effect
  • Choice of LFO waveform: sine, triangle, square, random, velocity sensitive etc. ( wave or mode )
  • Input and output volume ( gain , level or volume )

Famous audio samples


  • Thomas Görne: Sound engineering. 1st edition, Carl Hanser Verlag, Leipzig, 2006, ISBN 3-446-40198-9
  • Roland Enders: The home recording manual. 3rd edition, Carstensen Verlag, Munich, 2003, ISBN 3-910098-25-8
  • Hubert Henle: The recording studio manual. 5th edition, GC Carstensen Verlag, Munich, 2001, ISBN 3-910098-19-3
  • Thomas Sandmann: Effects & Dynamics. 5th edition, PPVMedien GmbH, Bergkirchen, 2006, ISBN 3-932275-57-8