From classic phaser tones of '70s rock and synth pop to next-level phasing, the Strymon Zelzah may just be the last phaser you'll ever want or need. It's a stereo phaser that has four phasers built in—two on each side. One side contains two four-stage phasers, offering classic, barber (continuous upward or downward), or envelope-controlled phase tones. On the other are two six-stage phasers built around a modified all-pass filter. You can use each side alone, run them together in series or parallel, or split their output to the left and right channels.