What Are Chorus Pedals (Guitar/Bass FX) & How Do They Work?


Chorus is perhaps the most popular of all the modulation effects in terms of guitar (and bass) pedals. A nice chorusing effect can make our instruments sound larger than they are and demand the listener’s attention without being overly obnoxious.

What are chorus pedals and how do they work? Chorus pedals are modulation effects units built into stompbox-style housing and are typically designed for guitar/bass. As an effect, chorus produces one (or more) copies of the input signal; modulates the phase of each copy, and outputs all voices to produce a widening/thickening of the sound.

In this article, we’ll further our comprehension of chorus pedals and how they affect guitar and bass guitar signals. We’ll discuss modulation more generally; I’ll share a few chorus pedals throughout the article, and I’ll offer some tips on how to get the most out of your chorus pedal(s).


Table Of Contents


What Is The Chorus Effect?

Before we get into chorus pedals and their inner workings, let’s discuss what the chorus effect is.

The chorus effect is named after the use of a chorus in music.

No, we’re not talking about the catchy singalong section of a pop song.

Rather, we’re defining chorus as a group of people singing or playing the same note in unison. Choruses are often found in choirs (along with other choruses singing harmonies) and sections of an orchestra.

The effect, in nature, happens because we’re not completely perfect beings. When a group of people sings the same note, there will be slight variations in timing and pitch between each voice and within each voice.

Of course, this is a good thing! We’re not robots or synthesizers, after all.

As the different voices produce the same note (with the inevitable variations mentioned above), they all converge and are perceived as one sound. A sound larger and wider than any one voice alone could be (even if the volume is the same).

Of course, no voice should be out of tune. A pleasant chorus effect has slight variations in pitch in the realm of cents rather than semitones. When done correctly, the effect will sound harmonically rich and shimmery and not “out-of-tune”.

To give one more acoustic example, the piano actually has its own chorus. Each key of a piano is attached to a hammer that strikes one or more strings. The higher keys of an acoustic piano strike 3 strings; the middle keys strike 2 strings, and the lower keys strike one string.

Though each string for a given note is tuned to the same note, there will be slight variations in pitch that cause a chorusing effect.

As an aside, the fact that the bass keys only have one strings gives us a hint: that chorus may be a poor choice for bass and sub-bass notes/frequencies. For the most part, this is true.

The chorus effect is such a powerful and useful technique that it has long been emulated via electronics. There are analog and digital chorus effects units that include software, rack units, and, of course, guitar/bass pedals, among other designs.

The chorus effect fits into the modulation effect category.

Chorus is a phase-shifting/modulation effect that utilizes a delay circuit to shift the phase of a signal and then combines the unaffected and delayed signals together.

Combining the modulated phase-shift signal with the dry signal causes the time-varying detuned effect known as chorus.


What Are Chorus Pedals & How Do They Work?

Chorus pedals are stompbox-style units designed to receive guitar, bass or other instrument signals at their inputs and electronically affect the signal to produce the phase-shifting chorus effect at their outputs.

These pedal work by having two paths for the input signal to travel:

  • A dry/direct path that leaves the signal unaffected.
  • A delay circuit path that phase-shifts the signal which is modulated by an LFO (low-frequency oscillator).

The two signals are then summed together at the output mixer to produce the chorus effect.

Modulating the delay time of the delay path will cause pitch variation in the signal. As the delay time is shortened, the waveform is slightly compressed, causing an increase in pitch/frequency. As the delay time is lengthened, the waveform is slightly stretched, causing a decrease in pitch/frequency.

The delayed signal only happens once, rather than repeating several times, giving a doubling (phase-shifting) effect rather than a delay effect.

As an aside, a vibrato pedal works in the same way except it doesn’t output the dry signal.

Note that stereo choruses will have two outputs but will typically share the same chorus circuit. The output of the chorus circuit (wet signal) will be sent directly to the summing mixer of one output channel (typically the left channel). It will be sent through a phase inverter before reaching the summing mixer of the other channel (typically the right channel).

A stereo chorus pedal can be used in mono by simply connecting to the left/mono output.

Some choruses will have two LFOs act upon their chorus circuit. These are known as bi-mode choruses.

There are other chorus designs but these are the basic (and indeed the building blocks for more involved chorus designs).

So a chorus pedal will effectively produce a copy of the signal; modulate the copy, and output a blend of the dry and wet signals.

It’s the blending of the dry and modulated signal(s) that produces the chorus effect electronically, just like it’s the blending of multiple voices that produces the chorus effect in nature.

The Design Of A Chorus Effect Signal Path

So how are chorus pedals built in order produce the chorus effect?

Analog chorus pedals are designed, essentially, as delay pedals with no feedback loop, and a low-frequency oscillator (LFO) that modulates the delay time of the delay (phase-shifting) circuit.

So while a simplified diagram of an analog delay pedal would look like this:

A chorus circuit will do away with the delay portion’s feedback loop so that the delayed signal is not repeated. To simplify the diagram above even further, we’d have:

Note that delay circuits are rather involved. Though beyond the scope of this article, it’s worth learning how delay pedals and units work to develop an even deeper understanding of chorus and modulation effects in general.

To learn more about delay pedals, check out my article What Are Delay Pedals (Guitar Effects) & How Do They Work?

For this article, just know that a delay circuit delays the affected signal relative to the original signal.

To illustrate the three basic types of chorus pedals mentioned above, I’ve added the following diagrams:

Here’s an over-simplified signal diagram of a mono chorus pedal:

The Electro-Harmonix Bass Clone (link to check the price on Amazon) is a great example of a mono chorus pedal designed for bass guitar.

Electro-Harmonix Bass Clone

Here’s an over-simplified signal diagram of a stereo chorus pedal:

The Boss CE-2W Waza Craft (link to check the price on Amazon) is a popular example of a stereo chorus pedal. It has a mono input and a stereo output (output A and B). Note that, by only plugging into output A, we’d achieve a mono chorus effect.

Boss CE-2W Waza Craft

Here’s an over-simplified signal diagram of a stereo bi-mode chorus pedal:

The Ibanez BC-9 (now discontinued) is one of the few pedal examples that uses a bi-mode (dual LFO) chorus circuit.

Ibanez BC-9

Some digital effects offer more than two voices. This multi-voice chorus effect is popular in synths and other dedicated chorus effects. Here’s an over-simplified signal diagram of a stereo multi-voice chorus pedal:

The DigiTech XMC (now discontinued) is a rare example of a multi-voice chorus pedal.

DigiTech XMC

Electro-Harmonix, Boss and DigiTech are all featured in My New Microphone’s Top 11 Best Guitar/Bass Effects Pedal Brands To Know & Use.

We can tell that typical chorus pedals are made with a single delay circuit modulated by a single LFO with either mono or stereo output options. The fact that the rare examples of bi-mode and multi-voice pedals have been discontinued tells us that there really isn’t a market for these more involed designs.

That’s good for us. It keep the price of the pedals down and makes them easier to explain in this article! I just wanted to show you a few different configurations to prime your mind before we get into the inner workings.

Chorus Modulation & The LFO

Now that we know the basic design philosophy of a chorus unit, let’s look into how chorus pedals modulate their signals.

As we’ve discuss, the modulation of a chorus pedal is controlled by an LFO.

A low-frequency oscillator, as the name suggests, is a wave with a low frequency. LFOs have frequencies below the audible range (20 Hz).

The LFOs used in chorus pedals have adjustable frequencies typically between 0.1 Hz to 6 Hz and above. Their waveforms are generally either sines or triangles.

We know, from the previous section, that the LFO will modulate the delay circuit of the chorus pedal. What exactly does it modulate? It modulates the delay time parameter of the delay.

Delay time, as the name suggests, refers to the amount of time the delay circuit will delay the signal. Delay times of chorus pedals tend to be in 18-24 millisecond range.

As an aside, vibrato and flanger pedals, which also utilize time-modulated delay circuits, have much shorter delay times.

Why does the chorus effect require a modulated delay time? There are two reasons. Let’s defer back to the natural chorus of two singers singing the same note to help explain.

The most obvious reason to modulate delay time is to change the amount of delay between the two voices. This happens naturally with a chorus of singers since each singer will not hit the same note at exactly the same time (remember the 18-24 ms range).

However, this modulation is less pronounced in the actual chorusing effect.

The second reason actually affects the sound of a chorus effect the most. This reason is that modulating delay time will modulate pitch.

If you’re ever adjusted the delay time of a regular delay pedal as a signal was running through it to an amp, you would have heard a change in pitch.

This pitch-variation/detuning happens because, as the delay time is being shortened, the wave of the delayed signal is experiencing a slight amount of time compression. This time compression shortens the waveform, thereby increasing the frequency (and pitch) of the waveform.

Conversely, as the delay time is being lengthened, the wave of the delayed signal is experiencing a slight amount of time expansion. This time stretching elongates the waveform, thereby decreasing the frequency (and pitch) of the waveform.

This can be thought of as a sort of electronically-manipulated Doppler effect.

Note that dedicated “pitch-shifting” pedals use a different method to affect the signal’s perceived pitch.

To learn more about pitch-shifting pedals, check out my article What Are Pitch-Shifting Guitar Pedals & How Do They Work?

Going back to the two singers, there will be slight variation/vibrato/detuning in their voices, even when singing a defined note.

By controlling the delay time with an LFO, we effectively turn the delay time knob up and down very quickly. To achieve a subtle chorus, the delay time typically oscillates in the range of 18-24 milliseconds. More intense chorusing effects can be achieved by varying the delay time beyond this range.

When the detuned modulates signal is combined with the direct signal, we get the chorus effect.

Increasing the frequency of the LFO will increase the speed of the chorusing effect. Increasing the amplitude of the LFO will increase the intensity of the chorus effect by increasing the amount of pitch/delay-time variation in the wet signal.

It’s important to restate that the chorus effect is a phase-shifting effect (just like phaser, flanger, and vibrato). However, unlike the phaser and flanger, chorus doesn’t produce the same comb-filtering effects in the frequency response.

This is because the phase-shifted copy and the original signal are rarely at the same frequency (due to the delay/pitch modulation). This minimizes phase cancellation while still technically utilizing the delay-based phase-shifting technique.

We’ll discuss the other phase-shifting effects shortly.

For now, we’ll wrap up this section on how a chorus pedal works to give us the chorus effect!

Note that digital chorus pedal utilize digital signal processing (DSP) to achieve the same outcome.


Chorus Pedal Parameter Controls

Speaking of the LFO parameters, let’s get into each of the controls we’d typically find on a chorus pedal to help further our understand of how these pedals work and how we can dial them in to achieve our desired results.

The typical parameters we’ll find on a chorus pedal are as follows:

Speed/Rate

The speed/rate control of a chorus pedal controls the frequency of the LFO and, therefore, the speed at which the pitch-variation happens in the wet signal.

A slower rate will produce a more subtle chorus effect. Increasing the rate will increase the perceived detuning of the effect as the phase-shifting will become more intense.

Depth/Intensity

The depth/intensity control of a chorus pedal controls the amplitude of the LFO and, therefore, the range of delay times the delay circuit will oscillate between.

Increasing the depth will increase the amount of pitch-variation (the difference in pitch above or below the original signal) that happens in the wet signal.

Mix

The mix control of a chorus pedal controls the level of the wet signal that is mixed into the dry signal at the output of the pedal.

Low-Cut Filter

A low cut-filter will remove some amount of the low-end from the detuned, phase-shifted signal. Phase shifting in the low-end, especially in stereo, can lead to poor results.

If we recall our discussion on the piano, we’ll remember that even acoustic instruments are designed to remove chorus from the low-end.


Tips On Using A Chorus Pedal

Here are a few points to consider to help you get the most out of your chorus pedal.

Subtlety Is Often Best

Chorus is one of those effects that sounds awesome when used subtly but can get out of control pretty quickly as the effect is cranked up.

Though the controls of your chorus pedal can certainly be turned all the way up, chorus is often best heard with the controls turned to more moderate levels.

Of course, experiment with your pedal to hear what it sounds like maxed out. Just know that the tone generally won’t be overly useful.

Focus On Playing Chords

Chorus, like other modulation effects, can really shine when there’s plenty of harmonic content in the signal. Chords afford us this harmonic richness.

Let The Chords Ring

Letting the chords (or notes) ring can also help to put the listener’s attention on the chorus effect. A busy guitar or bass part with lots of notes/chords in quick succession can take away from the chorusing effect.

That being said, perhaps a busy part ran through chorus is exactly what the music needs!

Use Stereo Outputs If Available

Many chorus pedals offer stereo outputs. Use them to widen/thicken the sound of your guitar/bass even further! The stereo outputs will typically invert the phase of one channel to really make the sound of the guitar stand out in the stereo image.

This is easier done in the studio. However, taking two amps on stage can allow us to tap into the stereo awesomeness of chorus!


Where Should Chorus Pedals Go In The Signal Chain?

Chorus pedals, like most modulation-type effects pedals, work best after the dynamic, pitch-shifting, synth and gain-based effects and before the time-based effects (delay and reverb).

This often puts them near the end of the pedal chain, mixed in with vibratos, flangers, phasers, uni-vibes, and the like.

Of course, this is just a suggestion. Try out different positions and listen for what sounds best to you when setting up the signal flow of your pedalboard!

To learn more about ordering pedals in the signal chain, check out my article How To Order Guitar/Bass Pedals (Ultimate Signal Flow Guide).


Other Phase-Shifting Effects

Now that we understand chorus pedals, let’s have a look at other effects that utilize phase-shifting:

Note that delay, doubling, haas effect, and more could be considered phase-shifting effects as well. This is because they use a delayed copy of the direct audio. Any delay could be considered a phase shift (though it could also be thought of as delay or, in the case of mixing, multiple tracks.

Flanger

Flanger works very similarly to chorus.

It produces a copy of the input signal (only one copy) and sends it through a delay circuit with a LFO-modulated delay time.

The flanger utilizes shorter delay times, which results in a sort of comb-filtering effect when the wet and dry signals are combined.

A flanger will utilize a feedback path to re-feed the delay circuit input. This increases the resonances of the comb filter.

The well-defined peaks and trough of the comb filter are then modulated via the LFO that controls the variation of the delay time.

With all that we have the classic sound of the flanger!

The Source Audio SA240 Mercury Flanger (link to check the price on Amazon) is an awesome flanger pedal with all the basic controls we need.

Source Audio SA240 Mercury

Source Audio is featured in My New Microphone’s Top 11 Best Guitar/Bass Effects Pedal Brands To Know & Use.

For more information on flanger pedals, check out my article What Are Flanger Pedals (Guitar/Bass FX) & How Do They Work?

Vibrato

A vibrato circuit is effectively a chorus circuit without any direct signal.

Vibrato is an effects that produces pulsating variations in pitch, raising and lowering the pitch around a desired note.

The input of a vibrato pedal is not copied. Rather, the entire signal is sent through a delay circuit that has its delay time modulated by an LFO.

The TC Electronic Shaker (link to check the price on Amazon) is a great vibrato pedal with the typical controls and a tone knob.

TC Electronic Shaker

TC Electronic is featured in My New Microphone’s Top 11 Best Guitar/Bass Effects Pedal Brands To Know & Use.

For more information on vibrato pedals, check out my article What Are Vibrato Guitar Effects Pedals & How Do They Work?

Phaser

The was a phaser works is a bit different than the other types of phase-shifting pedals mentioned here.

Rather than using (and modulating) a delay circuit, a phaser will utilize a series of all-pass filters to change the phase of certain frequencies in its wet signal. This signal will then be mixed back in with the dry/direct signal and the phase cancellation will cause the peaks and valleys in the output signal’s frequency response.

The defined frequencies are modulated by an LFO. A feedback loop in the phase-shifting circuit allows for greater resonances in the output signal’s sweeping peaks and helps to intensify the sound of the phaser.

The Boss PH-3 Phase Shifter (link to check the price on Amazon) is an excellent example of a phaser pedal with all the typical controls.

Boss PH-3 Phase Shifter

For more information on phaser pedals, check out my article What Are Phaser Pedals (Guitar/Bass FX) & How Do They Work?


Is it bad to plug a guitar into a bass amp? In practically all cases a guitar can plug into a bass amp without overloading it or causing damage. However, because bass amps are designed to amplify bass signals, which have less high-end frequency information, plugging a guitar into a bass amp may result in less treble than we’d want.

What effects do bass players use? Bass players, like guitarists, do not actually need pedals to sound great. However, common pedals and effects for bassists include:

  • Tuner pedals (not an effect)
  • Envelope filter pedals
  • Compression pedals
  • EQ pedals
  • Boost pedals
  • Overdrive pedals
  • Distortion pedals
  • Fuzz pedals
  • Chorus pedals
  • Synth pedals
  • Looper pedals

Related article: Do Guitar Effects Pedals Work With Bass Guitar?

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