Chorus effect

The chorus is in audio engineering an effect which so expresses a tone as would resonate at the same time a second similar tone and move it in space.

Principle

The effect can also be found in the natural acoustics, such as in those plucked instruments whose strings are clamped in a unanimous pairs ( upper pairs of strings with bouzouki, 12 -string guitar, etc.), as well as the piano, the hammers strike three strings at the same time, or bagpipes and organ when several similar whistling sound with each other. Also audible is the effect in a well- rehearsed choir - where the effect has its name.

If two sound sources at the same time have the exact same pitch, there is no chorus; a mere copy of the original source is therefore not sufficient. Only when the pitch of the copy a little different from the original, giving the impression of doubling and the beat. Therefore, the strings and voices within their groups in the above examples intentionally slightly out of tune, but only so minimal that the human listener does not feel the detuning to be wrong.

After this detuning principle can be applied with a simple natural echo a chorus effect to achieve, provided the original sound source varies with time in such a way their pitch, that at the time of the echo occurrence, the two sound sources, so original and echo, not more have the same pitch. This principle is also reversed: the echo varies its pitch, while the original remains constant; This is the case if gusts of wind speed up or slow down the relative velocity of sound echoes. Such modulated echoes are, however, referred to only in the broad sense as a chorus, in the strict sense of the Chorus is an effect without audible echo.

Full for carrying the chorus comes only with voiced and long tones, since it requires at least about a quarter of a second, until the typical beats come into play.

Technical implementation

Delay

Similar to flanging the chorus of the sound source to be processed produces a delayed duplicate; Chorus this delayed by about 15 milliseconds. This delayed replica is added to the stock. The delay can be made ​​both by means of software in audio applications, as well as digital or analog electronics, as well as with analogue tape technology. Unlike the Flanger uses shorter delay times, the phase cancellation and hikes are in the chorus only weakly, that is, the typical "jet -like" color the sound of the flanger (comb filter effects ) occur when Chorus less clearly. However, the delay in the chorus is still so short that the listener recognizes no echo, but original and duplicate as at the same time feels ( human echo threshold is above about 25 milliseconds).

Modulation

The core of the effect is that the delayed signal is periodically accelerated and braked. This process is called modulation. During the acceleration, the pitch is higher than the original, while the deceleration is lower. The result is the intentional slight detuning between the delayed and original signal.

The modulation of the time delay can be shown graphically as a shaft, such as a sine wave or triangular wave. Shaft graphics are commonly found on the labels of the chorus devices, but these usually do not describe the course of the time delay, but the the resulting pitch. For example, CE-1 Chorus Ensemble Japanese company Roland is a square wave form given to the boss, say, the sound is alternately high and continues to steadily deep. This is generated by a triangular wave in the time delay modulation. For steady shortening the delay time of the sound remains steadily high; with continuous extension he's ever deep; and without time change the pitch remains original. This principle is the same as the Doppler effect.

The body responsible for the modulation component is referred to as an LFO (Low Frequency Oscillator). Some chorus models have more than one LFO. As a simple example with a slow LFO, overlaid by a second faster LFO, create a more turbulent, more winding modulation curve in the sum.

Stereo option

Many chorus models offer the possibility to display the hover effect in stereo. Either this several independently modulated chorus signals in the stereo panorama can be distributed; or if only a chorus signal is available, this left and right mixed identical, but on one side with the reverse phase.

Problems in the bass range

At low frequencies, a delay time of 15 milliseconds lead to undesirably strong phase cancellation. A half- wave phase of 15 milliseconds duration corresponds to whole phase length at a frequency of 33 Hertz, so an important for bass instruments root. This, according to the modulation and the adjacent tones can be canceled by the chorus. To avoid this, there are special models chorus for bass guitars; in this case only the higher frequency spectrum is processed by the Chorus by high-pass, the lower left untreated.

Flanger and Chorus

The main difference with the flanger is that the chorus as aims more at doubling voices on timbre coloration; the Flanger, this weighting is reversed. In addition to the Flanger includes a feedback function that can send the delayed signal back into the delay line; the chorus does not have this function.

Other Techniques

In addition, a chorus -like effect can produce Shifter with a slightly detuned pitch.

Construction and operating

Chorus effects can be created with software and hardware. In hardware, the chorus is usually part of multi-effects units in 19 -inch enclosures, or as a ground effect machine with foot switch.

In the form of a floor effects unit, the controls are usually designed simply and offer the following basic parameters ( in brackets are the common English names):

• Speed ​​of the LFO, about 0.1 to 10 Hertz (speed or rate)
• Known amount of detuning, and depth or width (depth or width )
• Volume balance between the original and delayed signal ( mix)

More complex models have more parameters:

• Base delay time ( delay)
• Level of the original signal can be lowered to zero, for without vibrato chorus effect
• Choosing the LFO waveform: sine, triangle, square, random, velocity-sensitive, etc. ( wave or mode )
• Input and output volume (gain, level or volume )

Famous Sound Clips

• Andy Summers of The Police on the guitar.

• Kurt Cobain of Nirvana on guitar. Song: Come as You Are

• Eberhard Weber on his fretless bass.