The Chorus Effect: Everything You Need To Know

Bob Leggitt | Sunday, 29 November 2015 |

Chorus. What is it? Where did it come from? And how does a musician make the best of it? The chorus effect progressed from being completely overlooked in most facets of popular music, via a tepid greeting when introduced in its classic form during the mid 1970s, to being used and abused to death in the mid 1980s. On the doorstep of 2016, it’s still a hugely important effect, but generally, we use chorus with a lot more restraint today. In this post we’ll take a detailed look at what chorus is all about, how it moved around musical trends, and where it stands today...

Heading the post is an image of the Boss CH-1 Super Chorus pedal, which replaced the CE-3 Chorus in 1989. Whilst the CH-1 didn’t arrive on the scene until after the chorus craze had peaked, it epitomised what 1980s chorus was all about, adding high frequency EQ to optimise the jangle factor and facilitating something tantamount to rack FX fidelity in a footpedal. It was introduced in the UK at a price of £72 – just £3 more than the CE-3, and it was advertised by Tony Hicks of The Hollies, who’d recently had a chart-topping UK hit with a re-release of their golden oldie He Ain’t Heavy. The ad cited that the CH-1 pedal had finally prompted Hicks to replace his original Boss CE-1 Chorus Ensemble with the hi-tech newbie.


Chorus is a modulation effect, which, at its most basic, duplicates an audio input signal, subtly alters the pitch of the duplicate, and then mixes the duplicate signal with the original to produce a rich shimmer in the sound. The pitch deviation can either be a static shift (detune), or, much more commonly, a cyclic wavering. The speed of the pitch wavering cycle is usually controllable, and can be increased from an extremely slow ‘shallow sirening’, up to a rapid vibrato.

The large and weighty Boss CE-1 Chorus Ensemble pedal was introduced in 1976 as the first real standalone chorus effect. The circuitry for the CE-1 had already been employed in a version of the Roland Space Echo and the Roland Jazz Chorus guitar amplifier. It was a full stereo chorus which split the original signal and the pitch-modulated signal across two channels for a spacious richness. However, it took musicians some time to catch up with Roland’s vision and adopt the CE-1 en masse. The CE-1 pictured above is the one from Boss’s aforementioned 1989 ad with Tony Hicks.


Chorus is probably most closely associated with the pop music of the 1980s, but it’s much older than that. The real hotbed of early development in the world of man-made chorus was the Hammond organ, which introduced the concept of deliberately detuning one signal against another as early as the 1930s. Initially, this was a static detune, created physically, with a second, pitch-offset tone generation system. But the following decade, Hammond introduced the famous scanner vibrato effect, which facilitated the classic Hammond vibrato chorus. Vibrato chorus mixed the regular signal from the organ’s tonewheels with a vibrato-treated signal, producing a classy and distinctive animation.

Most of the intermediate steps between the Hammond developments and the widespread adoption of electronic chorus for pop instruments (and vocals, of course), were a sort of converging progression coming in from different angles. Roland’s final focusing of all the different ideas and concepts in the mid 1970s, was a critically important step, but it had lots of influences and precedents…

For example, studios, and subsequently instrumentalists, had been using the Automatic Double Tracking effect (ADT) after The Beatles implemented it in the mid 1960s. ADT drew on tape echo technology to offset a duplicate signal on top of itself. The effect was meant to simulate the sound of actual double-tracking – i.e. overdubbed unison singing or playing, which would be thickened by small pitch discrepancies between the two unison parts.

Meanwhile, a multi-oscillator analogue synth was able to produce similar thickening by detuning one oscillator against another.

And late ‘60s floor effects like the Uni-Vibe came close to electronically generating chorus whilst seeking to emulate a rotary speaker. Despite the use of the word “chorus” on the Uni-Vibe pedal (probably a misenterpreted lift from Hammond terminology), the actual sound was not really that of a chorus effect. The ingredients were there in the electronics, but presumably, there was no demand for straight chorus, so it was not made available.

Shortly before Roland’s final definition of classic chorus in the mid ‘70s, mashups of synthesizer and organ technology were approaching the same territory. A good example of this was encapsulated in the Solina String Ensemble of 1974. To create the string ensemble effect, the synth employed a built-in modulation/chorus system which lay somewhere in between a Hammond vibrato chorus and a Roland/Boss chorus in personality. The Solina’s effect, however, was more like an old-style organ chorus in that it had a preset cycle rate. Indeed, originally, the Solina's modulation effect could not be disengaged.

Hammond recognised the potential for, and importance of animation and detune decades before the pop world saw the light. Chorus was a part of electric organ architecture long before rock 'n' roll began.


The lush Roland/Boss chorus effect, when it arrived, became the basic template for most future chorus units. Some choruses brought in additional modulated signals for a deeper thickening, but the vast majority of chorus effects are based on the Roland/Boss design, with cyclic pitch modulation, variable for depth and rate. The variable cycle rate and depth were key features of the Roland/Boss chorus, allowing users to customise the effect to suit not only different playing styles, but also a range of different instrument types and sounds.

As I mentioned, most musicians initially gazed at the Boss CE-1 in wonder. But chorus began to gain a niche foothold in the late 1970s, and then went crazy in the 1980s.


Part of the reason that chorus didn’t really hit the forefront of pop music creation until the 1980s, I suspect, was that chorus relies on high fidelity to shine, and it’s not really needed when sounds are thick and full, as was the case through most of the ‘70s.

In the ‘80s, fidelity improved not only in the recording process, but also in the media offered to the consumer (audio tapes in particular) and in consumer playback systems. Suddenly, everyone wanted a bight, shimmering, clinical sound, and that’s where chorus came into its own. Chorus was the perfect foil for early digital synthesizers, which initially sounded very thin and in need of greater body. And chorus also helped add life to some of the clean, single coil guitar sounds, which began to replace the thicker sounds of rock and post-punk from around the dawn of the ‘80s.

In the world of guitar, Andy Summers’ work with huge commercial hitters The Police, brought chorus out of the niches and into the mainstream. Summers’ use of chorus (courtesy of a Jazz Chorus amp) was so blatant that at times it was almost as if he was a demonstrator for Roland. He also occasionally appeared to deliberately back off on rhythm and simply let chords ring, so as to highlight the chorus effect – a classic example can be heard in the track Walking on the Moon. This 1979 release prompted a lot of guitarists to rethink the way they played, and actually integrate effects into their playing, rather than simply adding them on top and hoping for the best.

Through the course of the early ‘80s, chorus was used widely in pop music and exploited by many of the bands involved in the era-defining New Romantic movement. Chorus became almost obligatory on guitars in some circles, and either chorus or its derivative the flanger were also applied very liberally to bass sounds.

Highly influential exponents such as Pino Palladino (Paul Young) and Mick Karn (Japan) were using modulation/delay effects to hugely ripen fretless bass sounds and drastically increase their prominence in a mix. Palladino’s contribution to Paul Young’s Wherever I Lay My Hat is a fantastic example. It’s often cited that these effects were flangers, and at the time some people used to refer to the effects as ADT – which was sometimes, but not always feasible. A flanger, however, is essentially a chorus with variable feedback, and if you keep the feedback level low, you lose the characteristic ‘jet’ flanging sound, and just get a very powerful depth of detune. That’s what you hear on those bass sounds. Wide detune.

Chorus became one of the staple effects in guitar multi-FX processors. Here we see chorus integrated into the first true guitar multi-FX unit - the Boss ME5.


By the mid ‘80s, chorus was being overused, and was in any case becoming stale due to its prominence through the first half of the decade. I can remember a time in 1986 (for me, the categorial low point in studio recording) when you’d actually have to ask studios NOT to add chorus! Some of them even put chorus on the drums. I was as guilty of overusing chorus as anyone else, but in retrospect it was a terrible era. Deluges of digital reverb everywhere, and if you DIDN’T want a gated snare I think you had to submit the request to the engineer in writing at least a week before the session.

It was out of that trigger-happy ethos and general mod-FX overload, that musicians steadily began to turn their backs on chorus effects. As people found new ways to thicken the sound of digital synths (often using cheap expanders), and trends changed in guitar tone, chorus began to retreat from the front line of pop culture. Grunge replaced poodle-cut metal, the blues revival arrived, synth pop shifted back towards analogue… By the time Britpop stormed the charts in the mid ‘90s, the heavily chorused guitar sounds that peaked about a decade earlier were a fading memory. Chorus was still being used, but much more subtly.

If you use a PC to record music, you can get some cool chorus effects for free, in the shape of this site's own Stomp King VST units. The three chorus-based virtual pedals are shown above. You can access them all via the Freeware Effects for Download page. Even if you don't use virtual recording techniques, you can get some useful additional info on chorus effects from the individual units' pages.


So where does that leave us? Well, chorus still has a place in popular music, and ultimately it can be used anywhere, and in any way you like. Typically, though, musicians will observe the lessons of time and use it with restraint. It’s still great for adding body to very clinical sounds, and it’s probably most effective in the realm of keyboards. It still suits old FM synths (or emulations thereof) very well indeed.

One great rule is to try and use chorus where elements of detune would occur naturally and be desirable, and not use it where they’d be undesirable. For example, a detuned acoustic piano doesn’t sound very classy and is considered technically incorrect, so using chorus on an acoustic piano sound in a track that’s meant to exude class and sophistication will usually be a disaster. But string ensembles naturally embrace some detune in uison lines, so chorus still sounds great on synthesised string ensembles.

Tonally, the areas that normally warrant the addition of chorus are frequency ranges that are a bit devoid of midrange, and have a bight top end. Chorus helps compensate for the lacking midrange by inserting animation, and it adds a shimmer to high trebles. Using it on overdriven or grungey sounds needs a lot of care and judgement. Gone, I think, are the rules of the ‘80s, when a guitarist could deluge a fattish distorted rhythm guitar in chorus and get away with it. A clean guitar seeking to mimic a jangly 12-string, however, would be a different matter.

Ultimately, think about what chorus is, and use it intelligently, to simulate the natural pitch discrepancies people love in musical components. Approach a chorus effect like that, and it’s hard to fail.

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