The Uni-Vibe (or UniVibe), also known as Jax Vibra-Chorus, is a footpedal-operated phaser or phase shifter for creating chorus and vibrato simulations for electric organ or guitar. Designed by audio engineer Fumio Mieda, it was introduced in the 1960s by Japanese company Shin-ei, and then released in North America by Univox in 1968.
It was intended to emulate the "Doppler sound" of a Leslie speaker. Though not very successful as a Leslie simulator, the Uni-Vibe became an effect in its own right, putting its stamp on tracks like Robin Trower's "Bridge of Sighs", Jimi Hendrix's "Machine Gun" and Pink Floyd's "Breathe".
The effect, though often associated with chorus, is in fact created through a staggered series of phasing filters, unlike the usually aligned filters of a normal phasing effect. Unlike most other phaser pedals, this is achieved without the use of op-amps.
The Uni-Vibe phase shifter was known for its throbbing, hypnotic pulse and lo-fi sweep. These unique effects set it apart from other modulation-type effects at the time.
The Shin-ei Uni-Vibe was also sold as a Univox product.