Phasers set to stun
Phasers are among the least understood of all effects, primarily because they’re often confused with chorus and flanger effects. This confusion is not helped one bit by the fact that one of rock’s most significant pedals – the Shin-ei Uni-Vibe – was billed as a chorus effect, but was in fact created using a technique known as phase shifting.
Phasers work by splitting the signal into two, sending one copy through one or more all-pass filters with a non-linear phase response. As you may know, if you play a signal against an out-ofphase copy, they will cancel each other out. Here, they are never precisely lined up, which results in peaks and notches in the resultant frequencies. More all-pass filters (or ‘stages’) mean more peaks and notches, and therefore a more interesting tone. The output may also be fed back into the all-filters, with some frequencies emphasised as a result.
The aforementioned Uni-Vibe was released under a number of names, among them Jax UniVibe-Chorus, and was tapped by luminaries such as Jimi Hendrix and David Gilmour.
The first rack-mountable phaser was Eventide’s Instant Phaser model PS 101. Released in 1971 for the price of $575, it was quite an exotic unit in its day, offering an internal oscillator and a built-in envelope follower.
Now a well-known brand, MXR’s very first product was the Phase 90 pedal, a diminutive yet distinctive (and very orange!) slimline box with a single knob for controlling the speed of the phaser’s characteristic sweep. Introduced in 1974, it’s still in production today.
1974 also saw the release of the ElectroHarmonix Small Stone phaser, designed by Dave Cockerell of EMS Synthi fame. Here, the single Rate knob was joined by a switch that enabled the user to change the tone colour.
“Phasers are among the least understood of all effects”