Let’s take a dive into the swirling, shimmering waters of modulation and investigate the evolution of chorus, flanging, and phasing. It’s no exaggeration to suggest that nearly every electric-guitar-based album of the past 40 years—and every hearty pedalboard—features one or more of these classic effects. Their development is integral to the soundtrack of our lives. In charting their history, I’ll cover a mix of classic pedals, vintage studio units, and elusive rarities, giving examples of their use in recorded music.

I’ve had a lifelong fascination with vintage and unusual recording gear and effects, and my company, Soundgas.com, specializes in supplying them. So effects are definitely my bag and I could fill this magazine just writing about vintage phaser pedals. But such passions tend to be personal, so inevitably there will be omissions in this article that, for some readers, are glaring, and for that I apologize.

As a certified delay freak, it’s perhaps odd that my favorite of the three modulation effects, phasing, involves no delay at all. And my favorite chorus pedal happens to be a flanger. And my favorite flanger is the Tape Phase Simulator. Confused? Read on.

Modulation Demystified

What’s modulation? A source signal is modified by another signal, which, in phasing, chorus, and flanging, is a wave created by an oscillator. Chorus and flanging use a modulated delayed signal mixed back in with the source (or dry) signal. The main difference between the two is that chorus requires a longer delay than flanging. Phasing requires no delay: A series of evenly spaced frequency notches are slowly swept across the frequency bandwidth, resulting in phase cancellation. Flanging uses 1 to 5 ms of delay and swept harmonically spaced frequency notches that create deeper phase cancellations. Chorus is very similar to flanging, but uses 5 to 25 ms of delay time to create a thickening or doubling effect, and is often used to shape or widen a stereo image.

What’s modulation? A source signal is modified by another signal, which, in phasing, chorus, and flanging, is a wave created by an oscillator.

The Hammond Organ Company was a pioneer in modulation, as they also were in the classic spring reverbs I covered in “Lords of the Springs” in the June 2018 issue. And the first electronic modulation effect was Hammond’s legendary Scanner Vibrato, which debuted in the mid 1930s. This was an electromechanical device that created a rich, distinctive chorus and vibrato effect. In 2015, Analog Outfitters resurrected this device as their Scanner, which was reviewed in PG’s January 2016 issue. That review includes an audio sample where you can hear the Scanner in action, and you can see a demonstration on YouTube, under the search term “Analog Outfitters The Scanner Vibrato & Reverb Effect Demo.”

All You Need Is Flange

If you take two tape machines or turntables and simultaneously play the same recording on each while manually slightly reducing the speed of one of them, you get flanging. Flanging got its name because you achieve this effect by pressing on the rim, or flange, of the tape reel. Or the term was coined by John Lennon—in response to a nonsense explanation of automatic double tracking (ADT) by George Martin. Whichever version you prefer, the technique predates the Beatles by at least a decade, and possibly two. Les Paul used acetate discs as far back as 1945 to achieve the effect, and David S. Gold and Stan Ross, the owners of Hollywood’s famed Gold Star Recording Studio, claim to have released the first commercial recording to feature flanging, “The Big Hurt,” by Toni Fisher, in 1959.

Abbey Road engineer Ken Townsend invented ADT in 1966, when John Lennon became tired of recording double-tracked vocals. A second tape machine, previously used as a delay, was varispeeded by an oscillator to mimic the subtle pitch variations of a separate performance. The creative possibilities of this process were not missed by the Fab Four, and Revolver features many examples, although the most famous, Lennon’s vocal on “Tomorrow Never Knows,” is not ADT but an actual doubled recording. The following year, Glyn Johns engineered the Small Faces at Olympic Studios and created one of the most distinctive examples of ’60s flanging: the single “Itchycoo Park.” After that, and, of course, the Beatles’ “Lucy in the Sky with Diamonds,” the studio gloves were off and tape flanging was all over classic ’70s recordings, from David Bowie’s “Station to Station” to Queen’s “Killer Queen” to the Eagles’ “Life in the Fast Lane.”


The Shin-ei Uni-Vibe was a descendent of the company’s Honey Psychedelic Machine and Jax Vibra Chorus—and Soviet propaganda radio transmissions.

Phasers Set to Stun

The first phaser devices came from the Far East, thanks to the propaganda transmissions of Radio Moscow interfering with Japanese medium-wave radio.

According to Shin-ei designer Fumio Mieda, the powerful signals bounced off the ionosphere, which varies in height, to create “changes in pitch, phase, and amplitude.” That inspired him to build the circuit that first appeared in the company’s Honey Psychedelic Machine and Jax Vibra Chorus. The latter became better known as the Uni-Vibe. Listen to “Machine Gun” by Jimi Hendrix on the live Band of Gypsys to hear the unmistakable sound of the Uni-Vibe at work.

In 1971, a young Tom Oberheim, the designer of many classic pedals and synthesizers, created the first phaser pedal for Gibson/Maestro: the 3-speed Maestro PS-1 Phase Shifter. The sound of Leslie speaker cabinets intrigued him, and he designed the PS-1 as a more compact option. It went on to sell 60,000 units and became very widely used by guitarists and keyboard players, and heralded the rise of the compact pedal phaser. John Paul Jones used a PS-1 live with Led Zeppelin on “No Quarter,” although the keyboard effect on the original recording was achieved by running the signal through an EMS VCS3 synthesizer. Three years after Oberheim’s PS-1, two of the most influential phaser pedals were introduced: the Electro-Harmonix Small Stone and the MXR Phase 90. Both have had many iterations over the years, and their enduring sonic appeal is a testament to their superb design.