An Introduction to Phasers

Introduction to Phasers: The Tastiest Modulation Effect

Phasers are one of the most versatile effects to be found in a guitar rig. By sweeping around the center frequency of one or multiple notch filters, they can make funky riffs a little more gooey and they can add motion and interest to slow or ambient passages. Pink Floyd, Jimi Hendrix, Jean-Michel Jarre, Eddie Van Halen, and Frank Zappa were all frequent users of various types of phase shifter.

I had a teacher in college who regularly reminded us that repeat signs in music don’t mean “copy and paste,” but rather “play it again.” His assertion was that playing something again brings all sorts of opportunity for minor changes in the nuances of music. While the human element in music ensures notes and rhythms will likely be played somewhat differently each time, phasers offer another opportunity to create automatic tonal changes over time.

What does a phaser do?

A phaser creates cuts in the high end of a signal with the placement of those cuts being modulated up and down to different places on the audio spectrum. This behaves like an automatically moving tone control, but only on a small group of frequencies.

Phasers work by creating one or several notch filters and modulating the center frequency of said filter(s). A notch filter is a type of circuit that attenuates a narrow band of frequencies. Plotted on a frequency domain graph, it looks like a deep and slightly curved V, with the center frequency being the deepest point.

Static notch filters are interesting in that their narrow band of operation can sometimes make it hard to identify what sounds different when running audio through them, especially with guitar. However, as we modulate the center frequency their effect becomes more pronounced and noticeable. It sounds a little like turning the tone knob on the guitar automatically, but without losing the entirety of the top end. It also sounds a bit like a wah pedal but without the heavy-handed, vocal nature inherent in that effect.

The filtering is accomplished by creating a phase difference at certain frequencies and then mixing those signals with the dry signal to cause frequency-dependent phase cancellation. The way in which this is achieved varies by design.

The Mutron Biphase used light dependent resistors, the MXR Phase 45/90/100 all use FETs, and the Small Stone uses operational transconductance amplifiers. While each design may operate in a different manner, all utilize a circuit that can cause phase cancellation at a certain frequency as well as a circuit that can change that frequency over time.

Phasers and Leslie Rotary Speakers

Phasers sound similar to the rotating Leslie speakers used with organs. A rotary speaker utilizes a rotating horn fed by a speaker. At slow speeds this creates an interesting swirling effect as the sound source moves and the waves bounce off of different surfaces in the cabinet and room. At high speeds it creates a watery Doppler effect. At both high and low speeds, there is a constant shifting in the tonal character (or timbre) of the sound.

The Leslie has historically been used with organs to add life and movement to an instrument that can feel static when played through traditional, non-moving speakers. This effect was later used on guitars, synthesizers, and even vocals on some recordings; check out the Grateful Dead’s “Rosemary” or the Beatles’ “Tomorrow Never Knows” and notice the swirling vocal sounds.

While phasers are not Leslie simulators per se, their effect is similar. The idea behind all modulation effects is to create tonal motion. While flangers are known to create a tubular swooshing and chorus creates doubled or detuned sound, phasers have a subtle and warm nature about them.

Flanging and chorusing utilize delay circuits which create far more notch filters in the spectrum than a phaser would have. This is referred to as comb filtering. Because of this intensified effect, they often have a somewhat harsh or metallic sound. Phasers tend to be more mellow and less overbearing.

Speed Controls

Many phasers have only one control. This is usually labeled as “Speed” or “Rate.” This control affects how quickly modulation happens or how often the center frequencies of the notch filters are shifted up and down.

A slow setting on a phaser can take so long to cycle that it barely sounds like it’s engaged until a chord or note is held. Slow settings are useful when you don’t want the phaser to be noticed, but you don’t want the guitar sound to feel static either. At higher settings phasers begin to sound watery and alien. This can be helpful in increasing intensity, emulating a Leslie on a tremolo setting, or just simply getting weird.

Stages of Phase Shift

Phasers will typically have a setting or spec relating to the number of phase shift stages in the circuit. There are some phasers on the market that allow the user to switch between 2, 4, 6, 8, or more steps or stages. For every 2 stages another notch in the spectrum is added. As a result, an 8-stage phaser might feel more obvious and heavily affected than a 2-stage phaser. While some designs allow for switching, most phasers have a fixed number of stages.

The MXR Phase 45, for example, is a 2-stage phaser and thus only creates one notch filter. The Small Stone is fixed as a 4-stage phaser. The Mu-Tron Bi-Phase consisted of two 6-stage phasers which would be cascaded into one another for 12-stages of phase shift.

Depth, Mix, Amount

Some phase shifters will have a “Depth,” “Mix,” or “Amount” control to affect how deep the notch filters cut. Under the hood this is done by mixing more of the phase shifted signal with the dry signal or by making the LFO’s control signal larger. Increasing the depth of a phaser can often lead to a darker sound with a more intense sensation of pushing and pulling.

Feedback, Resonance, Color

A “Color” switch is found on the Small Stone to introduce feedback into the circuit. As would happen on an envelope filter or wah pedal with increased resonance, this creates a more vocal phase shifting and a more obvious effect overall.

One of the most common mods with the MXR Phase 90 involves clipping or removing a feedback resistor to eliminate the feedback in the circuit, making it sound more mellow and less distorted. This mod is commonplace when making a block logo Phase 90 operate like a script logo Phase 90.

The Transmogriphaser has a “Feedback” control to adjust how much feedback exists in the circuit. Because the feedback is dependent on how intense the phase cancellation is, the depth and feedback controls interact with one another quite significantly.

Phase a Phaser Into Your Life

Pink Floyd’s “Have a Cigar” has some very gooey phase shifting to complement the repetitive nature of the groove being laid down. The Isley Brothers’ “Who’s That Lady?” mixes a more aggressive phaser effect with some fuzz on the heavily modulated lead sound to create a frustrated wail. One of the most popular recommendations for phaser listening is “Itchycoo Park” by the Small Faces so be sure to give that a listen as well.  

Music is all about the relationship between one moment and the next, whether we change chords, melody, rhythms, or timbre. Phasers are a great way to introduce timbral change without throwing-off the entire personality of your tone. They are less aggressive than a flanger or wah pedal and more flexible than tremolo or pitch shifting.

A phaser may not be appropriate for every situation, but if you’ve not played one they’re worth checking out. Our Transmogriphaser pedal is a lot of fun to use. The MXR Phase 90 and Electro-Harmonix Small Stone are also excellent designs for beginning your modulated explorations. Whether you like funk, rock, electronic music, or avant-garde experimental jazz, there’s a good chance one of your favorite records has some phaser on it. Your pedalboard probably wants some phaser on it too.