What Is a Chorus Effect? What Chorus Does and How to Use It

A chorus effect mixes a sound with one or more slightly delayed copies of itself whose delay time slowly wobbles. The tiny shifts in timing and pitch make one instrument sound like several playing together, which comes across as thicker, wider and shimmering.

It's named after the way a choir sounds fuller than a single singer: many voices, never perfectly in time or in tune. Chorus fakes that with a delay line and a low-frequency oscillator.

How does a chorus effect work?

1. Copy the signal. The input is split into the dry sound and one or more copies.
2. Delay the copies. Each copy is delayed by roughly 10 to 30 ms, too short to hear as an echo and long enough to sound like a separate player.
3. Modulate the delay time. A slow LFO moves the delay time back and forth. As the delay gets shorter or longer, the pitch of the copy rises and falls very slightly, like a tape machine speeding up and slowing down.
4. Mix them back. The wobbling copies combine with the dry signal. Where they line up and drift apart, you hear the thick, moving sound of chorus.

Stereo chorus usually modulates the left and right copies differently, so the sound spreads across the speakers. That's a large part of why chorus makes things sound wide.

What does chorus do?

In practical terms, chorus does three things: it thickens a sound, it widens it in stereo, and it adds slow movement. That's useful anywhere a part sounds thin, static or narrow.

• Clean guitar. The classic 80s use: shimmering arpeggios and chords. Still common in indie, pop and shoegaze.
• Synth pads and strings. Chorus turns a plain saw pad into a lush ensemble. Many classic analog synths had a built-in chorus for this reason.
• Electric piano. Gentle chorus on Rhodes-style keys gives that warm, wobbling tone.
• Bass. A touch of chorus on fretless or synth bass adds movement. Keep the low end out of it so the bass stays solid.
• Backing vocals. Light chorus spreads stacks and makes them blend.

Chorus controls

Here's chorus doing its classic job on a synth pad. Nova's Soft Strings preset runs two saw oscillators an octave apart with five unison voices, then adds its built-in Chorus at 60% and a little vibrato. Play a chord and listen to the width and slow movement.

What is a chorus pedal?

A chorus pedal is the same effect in a guitar stomp box. Most have rate, depth and level knobs, and some add tone, a mode switch or stereo outputs. Boss's CE-1 Chorus Ensemble, released in the mid-1970s, is usually credited as the first chorus pedal, and compact chorus pedals became one of the defining guitar sounds of the following decade.

Early chorus pedals used analog bucket-brigade delay chips, which gave them a slightly dark, warm character. Digital chorus pedals and plugins can be cleaner, or can model that analog tone. On a pedalboard, chorus typically goes after overdrive and distortion and before delay and reverb.

Chorus vs flanger vs phaser

These three modulation effects get confused because they all move and swirl. The difference is in what they modulate.

How to use chorus on guitar

On clean electric guitar, start with a slow rate and moderate depth, and set the mix so the chorus thickens the chords rather than making them warble. Run it in stereo if you can; the width is half the effect. On distorted guitar, use less, because distortion already fills out the sound and heavy chorus makes it smeary. On acoustic guitar, a very light setting widens a strummed part in a sparse mix.

Chorus vs doubler and stereo widener

A doubler is a close cousin of chorus: a short delay with gentle modulation, panned away from the dry sound so it imitates a second take. You can build one from a delay. Drift's Wide Doubler preset sets a free 28 ms delay with no feedback, 25% wow and full ping-pong, which is essentially a stereo chorus made from a tape delay.

A stereo widener spreads a sound without any pitch movement. Spread, our free widener, doesn't modulate anything; its Huge Chorus preset gets a wide sound from mid/side width at 180%, an 8 ms Haas delay and Mono Bass at 200 Hz. Use a widener when you want width with no wobble, and a chorus when you want movement. Haas delays aren't mono-safe, so check the result in mono.

How to use chorus without overdoing it

• Keep it out of the low end. Chorus on sub frequencies makes bass sound unstable and hurts mono playback. Many plugins have a low cut; if not, use it on a send with an EQ.
• Slow and shallow first. Start with a low rate and depth and increase until you hear it, then back off a little.
• Use a send for control. Chorus on a return lets you blend it under several parts and EQ it separately.
• Check in mono. Wide stereo chorus can thin out or shift in tone when summed. Make sure the part still works.

If you want a synth that already has chorus, delay and reverb built in, Nova has all three built in, each on a single knob.