Guitar Tone, Part 2: Phasing, Flanging, and Chorus

Last week's Notes & Lines post dove into the somewhat accidental discovery of the most basic guitar tone alterations: distortion, overdrive, and fuzz. In this post, the second of the guitar tone series, we'll take a look at some common modulation effects that might be lurking in your music collection.

Modulation involves changing one or more parameters--typically amplitude, frequency, and phase--of a signal. Techniques include the addition of a carrier wave to the original signal, or splitting the signal into two parts, changing one or both of them, and mixing them again. In guitar terms, modulation can add increased depth, wider dimensions, and subtle movement to an output tone.

Phasing, or phase-shifting, is a common modulation effect. Phasers split the signal into two parts and shift one of them out of phase with the original. When the signals are recombined, they create a "notch" at the point at which they're completely out of phase. By employing an oscillator, the phaser can vary the frequency of this notch point, creating a whooshing, Doppler-like effect. Most phasers contain more than one shifting stage, with the capacity to add multiple notches and peaks within the same time period, multiplying the Doppler effect.

Much like guitar distortion and fuzz, phasing had a somewhat accidental birth. The Uni-Vibe, an early guitar footpedal effects unit, was introduced in the 1960s to allow guitarists to achieve a rotary speaker effect that was popular on electronic organs at the time. Its tone more or less failed to emulate a rotary speaker, but the unit was a pioneering four-stage phase shifter that popularized the phasing sound. The Uni-Vibe used four light bulb circuits to achieve the initial phase shifting and an LFO to shift the notches around. Later pedals replaced the light bulbs with FETs, with certain models employing opamps with variable resistors. Almost all phasers allow the player to control at least the speed of the phasing, while others allow greater control over the waveform shape and resonance.

Flanging is often viewed as a companion effect to phasing, but its origin story is quite different. Analog flanging requires recording a signal on two separate tapes, then periodically slowing one of the tapes down by pressing a finger on the edge (or "flange") of the reel. When the signals are mixed together, a comb filter effect occurs to create a characteristic "jet plane" or "spaceship" sound. While flanging was allegedly used as early as 1959, and was definitely used by The Ventures for a few brief moments in a 1962 recording, many believe that George Martin and John Lennon coined the verb "flange," which was originally nonsense.

Like the analog version, solid-state flanging relies on mixing a signal with an exact time-delayed copy of itself, creating peaks and troughs in the waveform. Flanging sounds a lot like a more severe version of phasing; guitar flangers use similar technology as phasers but require significantly more control over phasing parameters. Flangers require hundreds of phase-shifting stages rather than a handful, and solid-state devices weren't possible until the development of suitably powerful ICs in the '70s. The 1977 A/DA Flanger, probably the first successful commercially available device, was made possible by the development of the SAD-1024 chip, a bucket-brigade device (BBD) IC with 512 stages.

Finally, a third related modulation effect is chorusing. Chorus effects use the double-signal flanging technique, except that the delays between signals are extremely short and narrow, making the signals slightly out of tune with each other and resulting in a quivering, spacious version of the original sample. The effect is theoretically similar to (and designed to emulate) a violin section or a 12-string guitar: when a number of strings are playing together, a few of them are likely to be just slightly out of tune and produce a more resonant sound with natural reverb. Like flangers, solid-state chorus devices didn't appear until the late '70s, when short-delay ICs became affordable. One of the first--and maybe best-known--songs to use solid-state chorus was The Police's 1979 hit "Message in a Bottle", and in later years Nirvana used chorus on their breakthrough album Nevermind, notably in the verses of "Smells Like Teen Spirit" and throughout most of "Come As You Are". Most modern chorus effects use digital technology, which simply adds delay and pitch modulation to a doubled signal. This results in greater capability and range, so much so that it can make listeners a little dizzy...

Image credits: Public domain | P.B. Rage / CC BY SA 2.0