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


Flanger is one of the most recognizable effects at a guitarist’s disposal thanks, in large part, to effects pedals. This “jet swoosh” effect has made its way onto countless records and is worth understanding!

What are flanger pedals and how do they work? Flanger pedals are stompbox-style units that affect audio signals (mainly for guitar or bass) with flanger. Flanger is a effect that copies an input signal and continually shifts the phase of one copy to produce a sweeping comb-filtering effect on the output signal.

In this article, we’ll further our knowledge of the flanger effect and how flanger pedals work. We’ll also discuss modulation more generally. I’ll share a few flanger pedals throughout the article and offer some tips on how to get the most out of your flanger pedal(s).


Table Of Contents


What Is The Flanger Effect?

The flanger effect is defined as a phase-shift modulation effect that produces a sweeping comb filter across a signal’s frequency response.

Flanging, as an audio effect is often described as sounding like a “jet plane swoosh” or “drainpipe”. It’s a tough effect to describe but once you’ve heard it and understood it, you’ll be able to recognize it again without issue.

A flanger doesn’t actually use EQ (equalization) to produce its modulated comb filter effect.

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

Rather, it uses a phase-shifting (delay) circuit to phase-shift a copy of a signal. It then mixes the original and phase-shifted signals together, causing constructive and deconstructive interference that results in a comb filter across the signal’s frequency response.

The notches and peaks of the comb filter are modulated to produce the sweeper/whooshing effect of the flanger.

The term “flanger” is reminiscent of the effect’s origin.

Flanging was first heard in the days of tape. A recorded track would be duplicated onto two different tapes on two tape machines.

Both machines would be played back in sync and their playback head outputs would be mixed into a third tape machine that would record them.

Someone would then be tasked with lightly pressing their finger on the flange of one of the reels of one of the playback tape machines. This would slow the speed of one reel, continuously shifting its phase against the untouched reel of the other machine.

This small but gradual shift in phase would cause the comb filtering effect known as flanger.

Of course, after the person would remove their finger from the flange, the two tape machines would be out of sync. Pressing a finger on the second machine could bring them back into sync while producing more flanging (this time sweeping in the opposite direction).

So by pressing on the flange of two in-sync tape machines, we could (and still can) produce the flanger effect, hence its name. Today, it’s easier to do it with electronic hardware or software.

Flanger circuits, whether analog or digital, will sweep their flanging effect upward and downward in a repeating motion (until they’re turned off).

Flanging effects unit, including pedals, have additional controls including resonance controls, width controls, and rate controls.

Let’s now dive deeper into flanger pedals and discuss how they work.


What Are Flanger Pedals & How Do They Work?

Flanger pedals are stompbox-style units designed to receive guitar, bass or other instrument signals. Their circuits are designed to modulate the phase of the signal and produce the sweeping effect known as flanger.

The basic flanger design has two paths for the input signal to follow:

  • A dry/direct path that leaves the signal unaffected.
  • A delay circuit path that phase-shifts the signal which is modulated by an LFO (low-frequency oscillator). The output of the phase-shifting path can be fed back into its input.

The two signals are then summed together at the output mixer to produce the flanging effect.

Modulating the delay time of the delay circuit will cause a continuous phase shift between the dry and effect signals. This is what causes the sweeping comb filter in the output (once the two signals are mixed together).

To really understand flanging, though, let’s back-track and begin by understanding phase.

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. 90º (along with 270º) is the mid-way way. This is important information to know when learning about flangers.

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 produces what is known as a comb filter. A comb filter is named after its comb-like appearance in a frequency response graph or EQ. A comb filter caused by the aforementioned 1 ms delay can be visualized across the entire frequency spectrum in the illustration below:

Note that, as the frequencies get lower, the period increases. 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.

When a signal is mixed in with a phase-shifted version of itself, regularly spaced notches are created along its frequency response. This is the basis of flanging.

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 Design Of A Flanger Pedal

So how are flangers pedals built in order produce their effect?

Analog flanger pedals are designed, essentially, as delay pedals with a low-frequency oscillator (LFO) that modulates the delay time of the delay (phase-shifting) circuit.

So while a simplified diagram of an analog delay pedal would look like this:

Here’s an over-simplified signal diagram of a flanger pedal:

The delay circuit effectively shifts the phase of one signal relative to the other in order to produce the aforementioned comb-filtering effect. In order to achieve proper comb-filtering, a flanger delay should be kept below 20 ms at the upper range.

As an aside, the chorus effect, which is very similar design-wise to flanger, uses longer delay times.

So we know how the flanger circuit produces the all-important comb filter. However, just having a comb filter would be pretty boring. In fact, it would be like having a bad EQ applied to the signal.

In order to achieve flanging, the comb filter must sweep across the frequency spectrum. This movement is made possible with an LFO (low-frequency oscillator) connected to the delay circuit.

A low-frequency oscillator, as the name suggests, is an oscillator waveform with a low frequency. Generally an LFO is described as being below 20 Hz. The best flanger sounds typically happen well below 20 Hz and even below 1 Hz (1 cycle per second).

A flanger LFO is generally a simple continuous waveform like a sine or triangle wave.

The LFO will be set to modulate the delay time of the delay circuit. As the delay time is altered, the phase-shift between the direct and delayed signal changes. This, in turn, causes the sweeping motion of the resulting comb filter, back and forth across the flanger’s frequency response.

As another aside, vibrato and chorus pedals use the same phase-shifting LFO setup to alter pitch and detune their signals. Flangers do the same. However, flanging is often modulated slower than chorus and vibrato, which makes the pitch-shifting/detuning a bit less pronounced.

So to clarify, the amplitude of the LFO will control the range of delay times and, therefore, the modulation of the phase-shift and the shape of the comb filter. The frequency of the LFO will determine the rate/speed at which the delay time and phase-shift are modulated and, therefore, the speed/rate at which the resulting comb filter will sweep.

To push the intensity of the flanger, a feedback loop is provided for the delay circuit.

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, increasing the feedback within the phase-shifting circuit has a direct effect on the resonances of the resulting comb filter. Increasing the feedback will make both the phase-canceling notches and phase-cohesive peaks more prominent in the output signal.

Note that the mix/blend of the two signals also has an effect on flanger intensity, though it mostly softens the notches. A feedback loop will actually make the filtering more resonant.

Let’s have another look at the aforementioned 1 ms phase-shifted frequency response that did not have any feedback (red line) and compare it 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.

And so that’s how a flanger pedal works without getting into the nitty-gritty of electrical schematics.


Flanger Pedal Parameter Controls

Flanger is perhaps the most versatile modulation effect. We can get chorus sounds out of a flanger pedal and flanger pedals will often offer chorus, vibrato, and perhaps even a few other effects.

To help us understand the full extent of a flanger pedal, let’s have a look at the common controls we’ll have:

Speed/Rate

The speed/rate control of flanger pedal controls the frequency of the LFO and, therefore, the speed of the flanger.

Slower rates are usually better when it comes to flanger though faster speeds can also be used to great effect.

Depth

The depth control of flanger pedal controls the amplitude of the LFO and, therefore the overall frequency range of the sweeping comb filter.

The Electro-Harmonix Stereo Electric Mistress (link to check the price on Amazon) offers a rate control along with a flanger depth control. As we can see, this pedal is a two-in-one flanger/chorus.

Electro-Harmonix Stereo Electric Mistress

Delay Time

The delay time control will either do the same thing as the depth control or it will set the base delay time for the flanger (which the LFO will modulate about). Remember that, for flanging, it’s best to keep the delay times short.

Width

The width control of flanger pedal is the same thing as the depth control. It controls how wide the sweep of the flanging effect will be.

Manual

The manual control of flanger pedal will control the base delay time of the phase-shifting circuit and, therefore, the centre point for the comb filter to sweep about.

The Boss BF-3 (link to check the price on Amazon) offers all the controls we’ve discuss thus far along with a resonance control, which we’ll get to shortly.

Boss BF-3

Feedback

The feedback control of flanger pedal affects the level of signal that is fed back into the phase-shifting circuit. As we’ve mentioned, adding more feedback to the flanger will cause an increase in the resonances of the comb filter and, therefore, the overall intensity of the effect.

Feedback is sometimes labelled as “regeneration or “regen”.

The MXR M117R Flanger (link to check the price on Amazon) labels its feedback control as regen:

MXR M117R Flanger

Resonance

The resonance control of flanger pedal also controls the amount of feedback the phase-shiting circuit receives, thereby affecting the resonances of the peaks and notches in the comb filter.

The Source Audio SA240 Mercury Flanger (link to check the price on Amazon) offers depth, speed, resonance and delay (manual) controls.

Source Audio SA240 Mercury

Mix

The mix/blend control of flanger pedal of the flanger pedal will control the amount of the phase-shifted signal that is combined with the dry signal at the output.

If a flanger pedal doesn’t have a mix control, the wet/dry blend is typically 50/50, where the most phase cancellation will take place.

Electro-Harmonix, MXR, Boss and Source Audio are all featured in My New Microphone’s Top 11 Best Guitar/Bass Effects Pedal Brands To Know & Use.


Tips On Using A Flanger Pedal

Here are a few points to consider to help you get the most out of your flanger pedal.

Give It A Break

Flanger is a very identifiable effect and can be very attention-grabbing in the context of a mix. Try giving the flgner pedal a break and only use it when it’s musically appropriate.

This may be counter-intuitive in getting “more” out of your flanger pedal. However, using it sparingly will really make the effect pop out when it comes time.

Keep The Signal Coming

Flanger modulation is awesome. Like any noticeable modulation, having a consistent reference signal will really allow us to hear the entirety of the sweeping sonic movement.

Even when playing busier riffs, try to keep a decent amount of signal (either by sustaining or playing more percussively) to hear the entire flanger sweep with greater detail.

Try The Stereo Output If Possible

If your flanger pedal has a stereo out, try using it to achieve a wider and wilder effect.

The stereo output of a flanger will have one output phase-inverted relative to the other, producing an almost super-modulated stereo sound.

Try going stereo in the practice room, studio, or live stage by plugging into two hard-panned inputs or into two separate amps.

Get A Chorus Effect Out Of It

Many flangers can double as a chorus effect.

Try it for yourself by ridding of any feedback and increasing the delay time.


Where Should Flanger Pedals Go In The Signal Chain?

Flanger 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 phasers, choruses, vibrato, 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 flanger 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.

Chorus

Chorus is very similar to flanger. In fact, it can thought of, design-wise, as a flanger without feedback and with longer delay times.

The effect of a chorus is to add another voice to the signal that is slightly out-of tune. Chorus units achieve this by altering the phase-shift (and, therefore, the pitch) of the “copied” signal and summing the dry and wet signals together at the output.

The result is a widening and thickening of the sound, similar to a chorus (multiple people) singing the same note, hence the name).

The Boss CE-2W Waza Craft (link to check the price on Amazon) is an awesome chorus pedal.

Boss CE-2W Waza Craft

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

Phaser

The was a phaser works is a bit different than flanger and the other types of phase-shifting pedals mentioned here.

Rather than using (and modulating) a delay circuit, a phaser will utilize a series of all-pass filters to change the phase of certain frequencies in its wet signal. This signal will then be mixed back in with the dry/direct signal and the phase cancellation will cause the peaks and valleys in the output signal’s frequency response.

The defined frequencies are modulated by an LFO. A feedback loop in the phase-shifting circuit allows for greater resonances in the output signal’s sweeping peaks and helps to intensify the sound of the phaser.

The Empress Effects Phaser (link to check the price on Amazon) is a superb digital phaser pedal.

Empress Effects Phaser

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

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

Vibrato

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

In other words, a vibrato circuit is effectively a flanger circuits without the direct signal or feedback loop.

Vibrato is an effects that produces pulsating variations in pitch, raising and lowering the pitch around a desired note. It typically has a more pronounced LFO (an LFO with greater amplitude) than other phase-shifting pedals in order to achieve the pitch altering effect it is designed to achieve.

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

TC Electronic Shaker

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

For more information on vibrato pedals, check out my article What Are Vibrato Guitar Effects Pedals & How Do They Work?


Can you run a bass through a guitar effects pedal? Guitar effects will typically work well with bass guitar signals and vice versa. Some pedals are designed specifically for a certain instrument but will still work with other instruments, though results may vary. The harmonic profiles or guitar and bass signals are similar enough to not cause significant issues in most pedals.

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

Is it bad to plug a guitar into a bass amp? In practically all cases a guitar can plug into a bass amp without overloading it or causing damage. However, because bass amps are designed to amplify bass signals, which have less high-end frequency information, plugging a guitar into a bass amp may result in less treble than we’d want.

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