What Are Phaser Pedals (Guitar/Bass FX) & How Do They Work?


Phaser is one of the most interesting audio effects in terms of it electronic design and the effect it has on audio signals. Guitarists. bassists and other musicians can benefit greatly from a phaser pedal in their rig/pedalboard.

What are phaser pedals and how do they work? Phaser pedals are stompbox units designed for guitar and/or bass. Phasers act to modulate the phase of select signal frequencies via a series of all-pass filters that are swept by an LFO. Phasers combine the direct and effected signals, which causes a series of sweeping peaks and troughs in the EQ.

In this article, we’ll deepen our knowledge of phaser pedals and how they affect guitar and bass guitar signals. We’ll also discuss modulation more generally. I’ll share a few phaser pedals throughout the article and offer some tips on how to get the most out of your phaser pedal(s).


Table Of Contents


What Is The Phaser Effect?

The phaser effect is this cool, sweeping, modulated, filtering, trippy effect that sounds awesome on guitar, bass and pretty much any other instrument.

It’s actually quick difficult to explain. Both as a sonic effect and as an electronic processor.

I’ve attempted to describe it sonically. Let’s try electronically.

The effect achieved by a phaser is the sweeping modulation of a series of peaks and notch filter in a signal’s frequency response. Phasers produce a series of peaks and notches within a signal’s EQ (frequency content) and they sweep these filters up and down within the audible frequency spectrum.

The number of peaks and valleys in a phaser circuit depends on the circuit. Some phasers allow us to adjust the number via the poles/stages control.

The width and rate of the sweeping effect is also adjustable.

We can also adjust both the resonance of the peaks and the attenuation of the notches to further define the phaser sound.

Adjusting these parameters will, of course, alter the sound of the phaser, making the phaser a versatile effect. That being said, the effect, when noticeable, is pretty identifiable as being “the phaser sound”.

Stereo phasers can take things a step further and have the same filtering motion in the left and right channels, only with one channel’s modulation being a bit behind the other. Things can get really interesting here.

So, then, a phaser is a stereo equalizer? Well, no.

Perhaps, because it’s a modulator (and sound similar to a flanger), it could be based on a short phase-shifting delay circuit? Again, this isn’t the case.

Phasers actually utilize a series of all-pass filters (which pass all frequencies and aren’t really filters on the surface level) to produce their effect.

The phaser effect is really cool and I had to do my research for this article. I’m glad to be able to share what I’ve learned with you. Let’s learn about phaser pedals and how they work!


What Are Phaser Pedals & How Do They Work?

Phaser pedals are stompbox-style units designed to receive guitar, bass or other instrument signals and produce the modulation-type phaser effect.

How they do so is rather interesting.

The MXR Phase 90 (link to check the price on Amazon) is one of the most popular phaser pedals to ever be produced and is ultra-simple with its single knob.

MXR Phase 90

MXR is featured in My New Microphone’s Top 11 Best Guitar/Bass Effects Pedal Brands To Know & Use.

Before we get into how phaser pedals (and phaser units in general) work, let’s first define what phase is.

What Is Phase?

Phase applies to waveforms. In particular, it is the location of a point within a wave cycle of a repetitive waveform.

A repetative wave will go through 360º as it completes one period (one cycle). At this point we can the phase 360º or 0º.

Let’s have a look at a simple sinusoidal wave with its phase degrees and period marked:

So we see that, with a simple sine wave (which has only one frequency), we have the 0º phase as at wave passes zero amplitude on its way upward; 90º is passed at the positive peak; 180º is the point at which the wave passes across the zero line on its way down; 270º is at the negative peak (trough), and 360º/0º is where we cross zero again on the way up and start the pattern over again.

As we can see, phase is closely related to time in sound waves. Recorded audio waves also have phase closely related to time, particularly during playback.

Of course, audio signals (including those from our guitars and bass guitars) are made of many different frequencies. The simple sine wave is just an easy way of illustrating phase.

Now that we know what phase is, we can look at phase shift. Phase shift is the key mechanic in the phaser effect.

Just as we can define a point within a period of a repeating waveform with phase, we can also define the phase shift between two identical waveforms with phase. Let’s look at a few examples:

Here is an illustration of two sine waves with a 90º phase shift:

As the red wave reaches 90º through its period, the blue wave is at 0º of its cycle.

Here is an illustration of two sine waves with a 90º phase shift:

As the red wave reaches 180º through its period, the blue wave is at 0º of its cycle. At this phase-shift, the two signal are said to be completely out-of-phase with one another.

If we were to sum these two waves, we’d have no output. The positive peaks of one wave would cancel the negative peaks of the other and vice versa.

Phase Shifting & Time

Let’s now turn our sights toward the relationship between phase and time to further our understanding of phase and phase shifting.

A full period of a sine wave is considered to be one cycle and 360º. The time is takes for the wave to complete one cycle is dependent of the wave’s frequency.

Let’s take a 1 kHz (kiloHertz) sine wave as an example. 1 Hertz means one cycle per second. A 1 kHz sine wave, then, has 1,000 cycles per second with 1 cycle/period taking up 1 ms (millisecond) of time.

Now let’s look at delaying the signal by 1 ms. This would result in a 360º phase-shift and the shifted signal would be 100% in-phase with the original:

What would happen if we delayed a 500 Hz sine wave by 1 ms? A 500 Hz sine wave has 500 cycles per second so each cycle would take up 2 ms. Delaying the signal by 1 ms would delay it by half its wavelength (180º phase shift) which would put the signals 100% out-of-phase with each other:

The above two instances are the extremes (100% in-phase or out-of-phase). As we approach a 0º phase-shift, two signals become more in-phase. As we approach a 180º phase-shift, two signals become more out-of-phase. This is important information to know when learning about phasers.

What if we doubled our 1 kHz frequency rather than halving it? A 2 kHz sine wave has 2,000 cycles per second or one cycle every 0.5 ms. Delaying a 2 kHz signal by 1 ms would put it 100% in-phase with the original.

There’s a frequency between 1 and 2 kHz that, when delayed by 1 ms, will become 100% out-of-phase with the original. That frequency is 1.5 kHz, which has a period of 0.666 ms:

To generalize, we have the following equations to represent the 100% in-phase and 100% out-of-phase frequencies of a given sine wave.

ω = 360 • t/p

where:
ω = phase shift (in degrees)
t = time difference between the original and shifted signal (in seconds)
p = period of the wave being shifted (in seconds)

Remember that if the ω = 360x (x is any integer number), then the shifted signal will be 100% in phase.

It the ω = 360x + 180 (x is any integer number), then the shifted signal will be 100% out-of-phase.

To keep with our example of a 1 ms delay/phase-shift, our in-phase frequencies would be:

  • 1 kHz
  • 2 kHz
  • 3 kHz
  • 4 kHz
  • 5 kHz, and so on

Our out-of-phase frequencies would be:

  • 500 Hz
  • 1.5 kHz
  • 2.5 kHz
  • 3.5 kHz
  • 4.5 kHz, and so on

This kind of phase filtering can be visualized across the entire frequency spectrum in the illustration below:

Note that, as the frequencies get lower, the period increased. A wave with a longer period is less affected, in terms of phase, by a given phase shift than a wave with a shorter period.

In the picture above, we see what is referred to as a comb filter.

When a signal is mixed in with a phase-shifted version of itself, regularly spaced notches are created along its frequency response. These notches resemble a comb, hence the name.

Note that the notches seem like they’re getting closer and closer as the frequency increases. That’s because the frequency scale is logarithmic by nature.

The Way A Phaser Shifts Phase

Flangers and chorus circuits utilize delay to phase-shift copies of their original signal. In fact, a flanger simply modulates the comb filter we’ve discussed above. We’ll get to these effects pedal types later in this article.

A phaser’s frequency response is not a true comb filter with equally spaced peaks and valleys. Rather, the phaser defines the number of peaks and valleys in the frequency response.

It does so with phase shifting. However, it does it in a different way than simply delaying the signal.

As I mentioned earlier, the phaser utilizes a series of all-pass filters to achieve its phase-shifting. The phase-shifted signal must then be combined with the dry/direct signal to produce the phase cancellation required of the phaser effect.

What Is An All-Pass Filter?

On the surface, an all-pass filter seems silly. As its name suggests, it’s a filter that allows all the frequencies to pass. That’s not much of a filter then, right?

Well, rather than affecting the EQ of a signal as a regular filter would, an all-pass filter affects the phase of specific frequencies within the signal.

To learn more about EQ pedals, check out my article What Are EQ Pedals (Guitar/Bass) & How Do They Work?

An all-pass filter can be visualized in this simplified diagram:

The all-pass filter splits the input signal into two copies.

The copy is run through a phase inverter that puts it 180º or 100% out-of-phase with the original.

The copy is then sent through a high-pass filter while the original is sent through a low-pass filter (or vice versa). The signals are then summed together at the output.

The basic phase-shifting part of a phaser unit (with 4 poles/stages/all-pass filters) could look something like this:

At the low-end, the frequencies will have 0º phase-shift compared to the original signal. At the high-end, the frequencies will have a 180º phase-shift compared to the original signal.

Frequencies in the middle will be attenuated by different amounts by either of the filters (though the sum of their amplitudes will be equal to the signal’s original frequency response). This means that the middle frequencies will have some amount of phase-shift.

The frequency where the phase shift reaches 90º is equally affected by the high and low-pass filters and is known as the “corner frequency”.

The high-pass and low-pass filters are complementary and don’t actually affect the overall frequency response whatsoever when once the signals are summed back together.

So then, an all-pass filter allows all frequencies to pass through it alters the phase of these frequencies.

A single all-pass filter (or “pole” or “stage” as it’s often referred to in the context of a phaser) would produce a frequency-dependent phase shift that would look something like this:

So if we were to combine this signal with the dry signal (which is what a phaser does), we would have a sort of low-pass filtering effect. The original signal would be at 0º across its frequency response and the phase-shifted signal would cancel it out more and more as the frequencies increased.

This result is certainly not conducive to the phaser effect.

In order to produce its effect properly, a phaser uses not one but a series of all-pass filters.

The Empress Effects Phaser (link to check the price on Amazon) is a digital phaser pedal that allows us to choose between 2, 4 or 3 stages.

Empress Effects Phaser

Empress Effects is featured in My New Microphone’s Top 11 Best Boutique Guitar/Bass Pedal Brands To Know & Use.

Let’s have a look at the frequency-dependent phase shifts that would happen as we add more all-pass filters (poles) in cascade:

Okay so what do we have here? Let’s begin with the 2 pole (sky blue) line.

When two all-pass filters are put inline, the phase shift will span from 0º to 360º. That’s an entire period! In this case the low end and high end will be perfectly in phase with the original signal and will be heard clearly out of the summing mixer.

The 2-pole phase shift passes 180º once, so there will be one notch in the output.

Let’s skip the 3-pole line for a moment and focus of the 4-pole phase shift (orange) line.

This phase shift starts at 0º in the low end and ends up at 720º (in phase: 360 + 360 = 720) at the high end. It’s also in-phase somewhere in the mid-frequencies at 360º.

The 4-pole line crosses 180º and 540º which means there will be two notches in the frequency response and we sum the wet and dry signals together.

The 4-pole output would look something like this:

Going back to the 3-pole (pink) line, we see that we run into the same issue as the 1-pole set up with a low-pass filtering effect happening in the high frequencies as the phase-shifted signal approaches 540º (180º).

In order to utilize 3-pole designs, a phaser will run the wet signal through a phase-shift circuit before it reaches the all-pass filters. By shifting the phase, a 3-pole phaser design can achieve a fuller low and high-end (though not perfectly in-phase) along with 2 notches.

Here’s an illustration of a 3-pole/3-stage frequency-dependent phase-shift plot with an initial phase offset.

Analog phaser units will generally offer 2 to 12 stages/poles and typically only even number options. Some phasers offer odd-number stages/poles.

Digital phasers can offer many more stages if need be.

A phaser with an even number (n) of stages generally has n/2 notches in the spectrum.

A phaser with an odd number of stages will generally have as many notches as the following even number.

Thus far we’ve been under the assumption that the summing amp and output of the phaser would have a 50/50 mix of the direct signal and the phase-shifted signal.

At 50/50, the phaser effect would be the most prominent. This is due to the fact that the filtering effect is caused by phase cancellations between the dry and wet signals. Having too much of either will reduce the amount of cancellation, the depth of the notches and the sonic effect of the phaser.

The TC Electronic Helix (link to check the price on Amazon) has a depth knob to control the mix of the dry and wet signals.

TC Electronic Helix

TC Electronic is featured in My New Microphone’s Top 11 Best Guitar/Bass Effects Pedal Brands To Know & Use.

The LFO & Modulation

So far we’ve discussed how a phaser’s phase-shifting circuit works and the effect that shifted signal has when it is summed together with the dry signal.

But this alteration in the output frequency response would be rather boring and typically wouldn’t improve the perceived sound of the signal (think of it as a poorly setup EQ).

To get the phaser effect, we need the notches within the frequency response to move rather than stay stationary.

This is achieved via a variable resistor that affects the corner frequency of each all-pass filter by altering both the high and low-pass filters within the all-pass pole/stage.

Each stage is affected by the same variable resistor.

This variable resistor (potentiometer) is not controlled by a manual knob. Rather it’s controlled with a low-frequency oscillator (LFO).

An LFO, as the name suggests, will oscillate at low frequencies. Typically this means below 20 Hz (the lower limit of the audible spectrum).

LFOs are typically a basic waveform. In the case of a phaser, they’re often a sine wave or triangle wave.

As the LFO alters the resistance of the pot, the corner frequency of each stage/pole is modulated upward and downward within the audible frequency spectrum. This, in turn, sweeps the peaks and notches of the frequency response up and down, creating the phaser effect!

Here is an updated version of the simplified phaser circuit knowing what we know now:

The frequency of the LFO determines the speed/rate of the sweeping effect of the phaser.

The Source Audio Lunar (link to check the price on Amazon) has a speed knob to control the frequency of its LFO and a shape knob to control its waveform.

Source Audio Lunar

Source Audio is featured in My New Microphone’s Top 11 Best Guitar/Bass Effects Pedal Brands To Know & Use.

The Feedback Loop & Phaser Resonance

To complete the phaser unit, we need a feedback loop in the circuitry.

Our completed (over-simplified) phaser diagram looks like this:

With the feedback control, we can feed some adjustable amount (amplitude) of the phase-shifted signal back into the phase-shifting circuit.

What does this accomplish?

Well, what happens at the output when we mix the direct and the phase-shifted signal together? We get our phaser-effected signal with the expected number of peaks and valley sweeping across the frequency response.

We can get a similar “affected” signal to go back into the phase-shifting circuit by combining the feedback signal with the original dry signal. This will produce deeper cuts in the notches of the phase-shifted signal and more noticeable resonances at the peak of the signal.

This causes more pronounces resonances in the peaks of the output signal and a more distinct “phaser sound”.

Let’s have another look at the aforementioned snapshot of a 4-pole phaser frequency response that did not have any feedback (orange line) and compare to the same circuit with some amount of feedback (blue line).

Like any feedback circuit, too much can produce undesirable run-away effects. Keeping the feedback/resonance control at a safe amount is essential.

The Boss PH-3 Phase Shifter (link to check the price on Amazon), like many other phaser pedals, has a resonance/feedback control (RES).

Boss PH-3 Phase Shifter

Boss is featured in My New Microphone’s Top 11 Best Guitar/Bass Effects Pedal Brands To Know & Use.

Note that the feedback loop is not delayed and so the LFO will effectively modulate the dry and feedback signals to produce the same notches and peaks in the output signal.


Phaser Pedal Parameter Controls

The performance of a phaser can be controlled by many different factors. Let’s discuss the most important and common controls we’ll have on a phaser pedal.

Common phaser pedal controls include:

Speed/Rate

The speed/rate controls the frequency of the LFO, which, in turn controls the speed at which the comb-type filter will sweep across the signal’s EQ.

A slower rate will be more subtle (with all else being equal).

Depth

Depth typically controls the intensity of the phaser effect.

The phaser effect is most prominent (with the deepest notches) when there is a 50/50 mix of the wet and dry signals, so depth could alter the mix.

It could also increase the amount of feedback within the all-pass cascade loop to increase the resonances of each peak in the phaser effect, thereby making the effect sound “deeper”.

Feedback

The knob labelled “feedback” will control the amount of the affected signal that is fed back through the phaser circuit. Increase feedback can get out of control. However, when done tastefully, we can increase the resonance of each peak within the comb filter and increase the intensity of the phaser.

Resonance

Resonance controls will simply increase of decrease feedback to affect the resonances of the output signal.

Width

Width controls increase or decrease the amplitude of the LFO and, thereby, increase the range of frequencies the phaser will affect.

Stages/Poles

The number of poles can be adjusted in some phasers. Remember that a phaser will produce 1 notch for every 2 poles. Increasing the number of poles will give a different, and arguably more obvious, phaser sound.

Mix

The mix, blend or amount controls the wet/dry mix of the direct signal and the affected signal.

Remember that the phaser is the most pronounce when the direct signal and phase-shifted signal are equally represented in the output mix. This is because the effect is based on phasing-out frequencies between two signals.

Read the manual to find out what the mix control actually means. It’s often the case that having the control fully clockwise will get you to 50/50 (rather than having 50/50 be at 12 o’clock as is the case in many other pedals.


Tips On Using A Phaser Pedal

Phaser pedals are a lot of fun to play through and to tweak the controls. It’s easy to get lost in the sound of a phaser whether it’s a new pedal or one that’s been on your board for a while.

Here are just a few tips to help you get the most out of your phaser pedal:

Give It A Break

The phaser effect is awesome. We all know that.

However, having it on everything can get a bit tiresome for the listening after the third or fourth song.

This seems counter-intuitive but you’ll actually get more impact out of your phaser pedal if you reserve it for parts that could truly benefit from it. In other words, try not to overdo it or use your phaser simply for the sake of using your phaser!

Keep The Signal Coming

Phaser sounds awesome on long chords.

It can also sound really cool on more percussive-style playing. When throwing down some funkier chords, try hitting some muted strums between chord changes and listen to the phaser continuously modulate.

The point I’m making here is that if the phaser is steadily outputting some amount of signal, we’ll be able to really tune our ear into the effect it’s having.

Set The Speed/Rate To The Rhythm Of The Song

Try setting the speed or rate of the phaser to the song you’re playing. This is made easier with digital phasers that have a tap tempo function.

Doing this can help to further lock in your playing the greater good of the song.

Try The Stereo Output If Possible

If the phaser has a stereo output and you have an extra guitar amplifier or preamp in your mixing console, take advantage of it.

Many stereo phasers will have two identical phasers modulated by a quadrature signal to put the left and right channel outputs a quarter wave (90º) out-of-phase from one another.

This can yield an awesome phaser effect and take your tone to the next level!


Where Should Phaser Pedals Go In The Signal Chain?

Phaser pedals, like most modulation-type effects pedals, work best after the dynamic, pitch-shifting, synth and gain-based effects and before the time-based effects (delay and reverb).

This often puts them near the end of the pedal chain, mixed in with vibratos, flangers, choruses, uni-vibes, and the like.

Of course, this is just a suggestion. Try out different positions and listen for what sounds best to you when setting up the signal flow of your pedalboard!

To learn more about ordering pedals in the signal chain, check out my article How To Order Guitar/Bass Pedals (Ultimate Signal Flow Guide).


Other Phase-Shifting Effects

Now that we understand phaser pedals, let’s have a look at other effects that utilize phase-shifting:

Note that delay, doubling, haas effect, and more could be considered phase-shifting effects as well. This is because they use a delayed copy of the direct audio. Any delay could be considered a phase shift (though it could also be thought of as delay or, in the case of mixing, multiple tracks.

For more information on delay pedals, check out my article What Are Delay Pedals (Guitar Effects) & How Do They Work?

Chorus

Chorus is a modulation effect that produces a copy (or multiple copies) of the input signal and delays the phase of each copy relative to the original.

This is done with delay circuits (yes, just like on a typical delay pedal).

The copied signal is sent through a delay circuit and an LFO alters the delay time. Altering the delay time will also alter the pitch as the waveform gets slighty stretched (as the delay time is increased) or slightly compressed (as the delay time is decreased).

What we get is a sort of vibrato effect on the wet signal(s). Combining the phase-modulated copy/copies back with the dry signal produces the chorus effect.

Chorus produces a widening/thickening of the sound similar to if a chorus of people were singing the note (hence the name). Not everyone would be perfectly on pitch the entire time (in typicaly circumstances) and the chorus effect emulates this electronically.

The Hartke HC33 (link to check the price at B&H Photo/Video) is a great example of a chorus pedal that sounds great on bass guitar.

Hartke HC33

To learn more about chorus pedals, check out my article What Are Chorus Pedals (Guitar/Bass FX) & How Do They Work?

Flanger

Flanger works very similarly to chorus.

It produces a copy of the input signal (only one copy) and sends it through a delay circuit with a LFO-modulated delay time.

The flanger utilizes shorter delay times, which results in a sort of comb-filtering effect when the wet and dry signals are combined.

A flanger will utilize a feedback path to re-feed the delay circuit input. This increases the resonances of the comb filter.

The well-defined peaks and trough of the comb filter are then modulated via the LFO that controls the variation of the delay time.

With all that we have the classic sound of the flanger!

The TC Electronic Vortex (link to check the price on Amazon) is an awesome flanger pedal with all the basic controls we need.

TC Electronic Vortex

For more information on flanger pedals, check out my article What Are Flanger Pedals (Guitar/Bass FX) & How Do They Work?

Vibrato

Vibrato is an effects that produces pulsating variations in pitch, raising and lowering the pitch around a desired note.

A vibrato circuit is effectively a chorus circuit without any direct signal.

The input of a vibrato pedal is not copied. Rather, the entire signal is sent through a delay circuit that has its delay time modulated by an LFO.

The TC Electronic Shaker (link to check the price on Amazon) is a great example of a vibrato pedal.

TC Electronic Shaker

To learn more about vibrato pedals, check out my article What Are Vibrato Guitar Effects Pedals & How Do They Work?


Can you use guitar effects pedals for bass? Effects pedals are often designed for guitar but will universally work with bass guitar as well so long as the connection is correct (typically a 1/4″ patch cable). Some pedals may have difficulty tracking the lower octave of the bass guitar but all pedals can work with bass guitar.

Related article: Do Guitar Effects Pedals Work With Bass Guitar?

Where do fuzz pedals go in a pedal chain? Fuzz pedals typically work best at the very beginning of the pedal chain because they fundamentally alter the waveform of the guitar signal. Not only do fuzz pedals affect clean guitar/bass signals better than modulated/time-varied signal but the pedals after the fuzz (modulation and time-based effects) will sounds better as well with fuzz before them (rather than after).

Related article: Guitar Pedals: Boost Vs. Overdrive Vs. Distortion Vs. Fuzz

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