Phasers set to stun

Computer Music - - Make Music Now -

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”

Even­tide beat every­one to the punch with their In­stant Phaser Model 101, the first rack-mount­able phaser

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