Set Phasers to Stun: The History and Uses of the Phase Shifter


Straight out of a late 70s science fiction movie, the iconic phaser pedal is one of the most influential sounds of the last 50 years. Originally pioneered in the late 1960’s, the phaser effect gained massive popularity in the decades following after psychedelic guitarists like Jimi Hendrix and Robin Trower incorporated the wooshy, sweeping sounds into their style. Today, the phase shifter effect is favored by artists across the musical spectrum, from electric keyboardists to guitarists in rock, jazz, hip-hop, and more to producers and recording engineers working in many different styles to sound designers for films and video games. 

But what exactly defines a phaser effect? What are basic control parameters of phaser pedals? How does a phase shifter differ from other modulation effects like chorus and flange? What are some popular and historical examples of the phaser pedal? And finally, what are some popular musical examples of the phaser effect to provide inspiration for creativity and further research? Let’s dive in.

What defines the phase shifter effect?

The phaser is a modulation effect that shifts the phase of one signal in a pair of audio signals to create a constructive or destructive interference pattern between the two signals. At its most basic level, an audio signal enters the effect and is split into two paths. One path, called the dry signal, is not affected by the phaser. The other path, called the wet signal, passes through a sequence of four to twelve (or more) all-pass filters. These all-pass filters are then modulated with a low frequency oscillator, or LFO. The LFO’s modulation of the wet signal passing through the all-pass filters creates an interference pattern with the dry signal. The modulated wet signal is then mixed back with the unaffected dry signal on the output to create the phaser effect. 

What are some basic control parameters?

The four most common and basic parameters on phase shifter pedals are rate/speed, depth, feedback, and level/mix/blend. Some of these parameters have multiple names like rate and speed or level, mix, and blend, but they essentially control the same functions.

The rate/speed setting controls the rate/speed of the LFO’s movement through the all-pass filters. A slower rate/speed setting will produce a more gradual shift through the frequency range while a faster rate/speed will produce increasingly intense waves of sonic disorientation.

The depth setting controls the range of the LFO’s modulation. A lower depth setting limits the range of the LFO while a higher depth setting increases the margin of the interference pattern, generating a more heavily modulated tone.

The feedback setting controls the amount of output signal that is fed back into the input. Lower levels of feedback will not have a significant impact on the tone, but higher feedback levels will produce a cascading snowball of overtones than can overwhelm the output signal completely. 

Finally, the level/mix/blend setting controls the balance between the dry and wet signals on the output. A level/mix/blend setting of 0 means only dry signal reaches the output. A level/mix/blend setting of 100 means only wet signal reaches the output. This control is not found on all phasers as it can be difficult to achieve with analog phasers, but it is more commonly seen in digital phaser pedals.

How does the phaser differ from the chorus and flanger?

The phaser, chorus, and flanger are all related modulation effects. All three rely on a similar sequence of events to produce their distinctive sounds. All three effects split an audio signal into at least two separate pathways, a dry signal and a wet signal. All three depend on an LFO to modulate the wet signal and all three affect the interference pattern of the two audio signals in some way.

The primary difference between phaser, chorus, and flanger effects is that the phase shifter effect does not use a delay to alter the interference pattern of the two audio signals. Instead, the phaser effect relies on the LFO’s modulation of the all-pass filters to produce constructive or destructive interference between the two signals. Contrast this process with the chorus effect, which uses an LFO to modulate the pitch of the wet signal, and the flanger effect, which uses an LFO to modulate the delay time of the wet signal. 

Phaser, chorus, and flanger differ in one other significant way. In the chorus and flanger effects, the LFO’s modulation of the wet signal applies to all the frequencies in the signal. This produces a uniform phase shift across the entire audio signal. However, because of the LFO’s sweep through a sequence of all-pass filters, the phaser effect offers a degree of unpredictability in the interference pattern. Additionally, according to Steve Howell at Sound on Sound:

“(the) phase differences in the output signal that depend on the input signal frequency — for example, the phase of a low frequency might be shifted by one quarter of a wavelength, whilst a higher frequency will be phase-shifted by a different amount.”

This difference in process is what characterizes the doppler-like whooshing sound of the phase shifter effect as compared to the more wobbly and watery sounds of the chorus and flanger.

What are some popular and historical examples of the phase shifter pedal?

The Shin-ei Company’s “UniVibe” was the first successful phase-shifting stompbox pedal. The UniVibe had only two controls, a volume knob and an intensity knob, which could also be controlled via a connected expression pedal. Psychedelic tones emanated from a sequence of four all-pass filters and the effect took hold with guitarists like David Gilmour of Pink Floyd and Jimi Hendrix, giving the phaser effect the initial boost it needed to gain popularity.

In 1971, Eventide released the first rackmount phaser effect, the Instant Phaser model PS 101. According to Eventide’s product description:

“The Instant Phaser employed a series of eight, FET-based, carefully tuned analog all-pass filters which delivered lush phasing while preserving the original tone.”

Contrast the four all-pass filters of the Shin-ei Company’s “UniVibe” with the eight all-pass filters of the Eventide PS 101 and you can see how quickly things can progress with the increasing abilities of technology. However, more complex effects are not always superior. Three years later in 1974, the MXR company released its first product, the Phase 90. Versions of the Phase 90 are still in production today and remain among the most popular phaser pedals in history. The Phase 90’s greatest strength lies in its simplicity: the Phase 90 features a single knob for controlling the speed of the phaser’s sweeping effect. 

1974 also saw the debut of the Phase 90’s chief rival, the Electro-Harmonix Small Stone. Similar to the Phase 90, the EHX Small Stone is a four-stage phase shifter with a control knob for rate and a switch labeled “color”, which according to the owner’s manual:

“… changes the sound of the phase shift between a full and robust phase shift … to a more pronounced instance phase shift … Fundamentals and harmonics glide in and out for an extremely pronounced shifting effect.”

Both the MXR Phase 90 and the Electro-Harmonix Small Stone have passed through many phases in their production and remain two of the most popular phaser effect pedals in history.

Examples of the phaser effect in popular music

Here are a few great examples of the phaser effect in popular music:

Led Zeppelin – “Kashmir”

Listen to the frequency sweeps on the drums in Led Zeppelin’s classic “Kashmir”

Van Halen – “Ain’t Talkin’ ‘Bout Love”

Eddie Van Halen was iconic for his early adoption of the MXR Phase 90. Eventually, he teamed up with Dunlop to issue a line of signature Phase 90 pedals. The main guitar riff on “Ain’t Talkin’ ‘Bout Love” is a prime example of the phaser in action.

Tame Impala – “Solitude is Bliss”

Listen to the whooshing, sweeping frequencies of the guitar track in Tame Impala’s “Solitude is Bliss” for a great example of the phaser effect in modern music.

Neu! – “Hallogallo”

Check out “Hallogallo” by German krautrock pioneers Neu! for a great lesson in the uses for the phaser pedal.


The phaser pedal is an effect with unlimited creative potential. From subtle, swirling frequency shifts to all-out tonal disorientation and all spaces in between, the phaser makes a great addition to any pedal board or recording studio setup and is required knowledge for any aspiring musician.  

One Response

  1. To miss the first ever true Phase Shifter effect (by Maestro) in an article like this is akin to an author overlooking the Beatles in a piece on the British Invasion. Otherwise, nice. fwiw

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