Understanding the Modulation Guitar Effects Pedal Category
What is modulation and how does it work in an electric guitar (or bass) rig? What exactly do modulation pedals do to your signal? This article explores and answers those questions.
The clean tone of a guitar is a beautiful thing, particularly if you assume a quality amplifier with a carefully tuned three-band EQ and a touch of reverb. Yet, even the sweetest, warm-sounding tube amplifiers aren’t always enough. Great tone — and many great tracks — are established by layering sounds (guitars, in our case), either literally, with multiple tracks of one instrument, or with effects mixed into the clean signal.
This mixing of effects with a clean guitar tone gives us two types of signals:
- A “dry” signal
- A “wet” or effected signal
In this article, I’m going to discuss the “effects” side in terms of modulation. We’ll define modulation in a guitar context and talk about how we can use it to improve and layer our clean signal.
Let’s start with a basic definition of modulation in a guitar rig or effects pedal.
After that, we’ll get into the more technical issues.
What is Modulation to a Guitar Player?
Without getting too technical, modulation in an electric guitar rig is typically used as a parent category of waveform manipulation that includes the following effects pedals or processors:
- Chorus/Vibrato — Modulate the pitch and mix with original signal
- Flanger — Modulate the time and mix with original signal
- Tremolo — Modulate the volume and mix with original signal
- Phaser — Modulate the phase and mix with original signal
Any pedal or signal processor that produces one of those sounds would be categorized as a modulation effect, whereas something like reverb or delay would be categorized as ambient or a “timed” effect. From a guitarist’s perspective, that’s the simplest way to understand modulation at a surface level.
Beneath the surface, modulation is a far more technical matter that requires a basic understanding of signal processing.
To get how modulation impacts your guitar’s tone, the technical side is worth digging into.
A Technical Understanding of Modulation in a Guitar Rig
In signal processing, modulation can be broadly understood as altering or varying an existing sound wave. Effects processors can accomplish this in any one, or combination of the following ways:
- Varying signal strength over time
- Varying pitch
- Mixing the dry signal with a signal generated by a carrier wave
- Splitting a signal, altering one and mixing it with the unaltered signal
This is typically understood in the context of radio waves or manipulating amplitude, where you have three variables:
- Input (original signal)
- Carrier
- Modulated result
This gives way to some extremely complex physics equations and functions, which we don’t need to worry about (although you can if you want to). It’s much easier to understand graphically. This graphic represents three types of modulation, where each “column” can be observed from top to bottom:
An easy takeaway from this kind of diagram is that you have an original signal that is split into two parts, giving you an input and carrier signal running side by side which, upon being reunited, form the modulated result.
For guitar players the general intent of modulating waveforms is to add depth, layers and intensity to a signal without necessarily distorting it. Thus, modulation itself is not an effect, rather a process by which effects are produced.
Modulation itself is not an effect. Rather, it’s the process by which an effect is produced.
Effects processors do this by manipulating the carrier signal, either by delaying it or changing the pitch, before blending the two waveforms back together into one result. This creates a series of peaks and notches in the waveform, which can emphasize different frequencies at different points of a 360 degree cycle through each wave.
By this process we now have our layers, which could be described as follows:
- Variance in pitch + original (clean) signal
- Variance in timing + original (clean signal)
- Variance in blending between the two signals
By manipulating the carrier signal and combining it back into the original signal, you can create a wide variety of different sounds and effects.
MORE ON THE RELATIONSHIP BETWEEN MODULATION AND EFFECTS LAYERING
Effects that are generated by waveform modulation make the most ideal layering tools for several reasons:
- The pedals usually provide a “mix” control which allows you to change the balance between an effected and non-effected signal (input and carrier signal)
- Most modulation doesn’t significantly impact the timing of your signal
- They don’t add gain or distortion to your signal
- They can be extremely subtle and “thin” in terms of their saturation levels
When I want to layer a clean guitar signal, the easiest way to do this is with a really subtle modulation effect. In the example below, I use a Boss BF-3 flanger pedal to add a thin layer of modulation over a simple chord progression:
Here’s the actual audio I recorded:
https://www.guitarchalk.com/wp-content/uploads/2017/02/Light-Thin-Flanger-Layer.mp3
Anytime you need a little more than just a raw, clean electric guitar signal, modulation-based pedals are great options for adding texture. The fact that it doesn’t drastically change the tone is a good thing.
WHERE DO MODULATION PEDALS FIT IN A SIGNAL CHAIN?
This means that modulation effects have a very specific role in a guitarist’s pedalboard, which also means that they should have a specific location in your pedal chain.
Most conventional wisdom places them this way:
- Before ambient effects (time-altering effects like delay or echo)
- After distortion and gain-impacting effects
In the example below, the blue chorus and black tremolo pedals serve as our example modulation effects:
As you can see, they’re placed after the overdrive, but before reverb and delay. This is widely accepted as the most optimal way to place modulation effects. Part of the reasoning behind this arrangement is that many modulating effects processors use time delay chips and circuits that are similar to those found in delay, reverb and echo pedals.
It’s better to send an established volume level into a modulating circuit.
The main difference with modulation effects is that the time manipulation is far smaller, thus they’re better off to process before pedals that could potentially inflict a more drastic timing change on your signal.
We see overdrive, volume and compression (any effect that could impact gain levels) come first because it’s better to send an established volume level into a modulating circuit.
If you flip it around and send an already modulated circuit into a pedal that changes gain, you’ll lose — or unwittingly increase — the intensity of the modulation because of the change in gain levels.
Modulation by Effect
Now that we’ve seen some broad implications of modulation, it’s helpful to also look at it in the context of each individual effects processor. Again, keep in mind that modulation is simply the altering of a waveform, making it a parent category of the effects pedals we mentioned.
As a result, you won’t see a simple “modulation pedal.” To get our pedals, and the application of the science behind modulation, we need to get into individual effects processors and how they modulate the carrier signal.
We’ll cover chorus pedals, flangers and phasers.
Chorus pedals are up first.
Modulation in Chorus Pedals
Circuits in a chorus pedal split the signal of your guitar and slightly alter the pitch of the carrier signal, then re-combine the two paths to create a choir-like sound or the illusion that there are multiple instruments playing the same thing. The difference in pitch creates a very slight de-tuning effect, meant to give off the naturally-occurring differences in pitch between multiple instruments or voices.
Certain chorus pedals, or settings therein, might also add a slight delay to the carrier signal to create a more chaotic or “wet” effect.
Chorus is technically a type of delay, but a very short one, with sonic implications that put it firmly in the modulation category.
It’s an effect that is best implemented in stereo, with some expanse and space, perhaps between multiple speakers or tonal sources, allowing for a more broad and natural movement of the effect before it reaches the listener.
The effect has been described as having a “liquid” or “shimmering” quality to it, having been used on many guitar tracks since the release of Boss’s CE-1 in the late 1970s. Kurt Cobain is probably the most popular of these users, as the EHX Small Clone chorus was a mainstay on his pedalboard throughout the height of Nirvana’s popularity.
CHORUS PEDAL USES
While the chorus effect has been applied in all kinds of different tonal and musical scenarios, there are some best practices that have been established over the years. These methods take advantage of the chorus’s subtle delay and ease of use, making it a familiar layering effect.
Here are a few common uses I’d recommend keeping in mind:
- As a low intensity layer of modulation
- As a covering for a clean electric guitar signal
- As a dimensional expansion for a clean bass signal
- For layering acoustic guitar lead melody or chord progressions
DIGITAL VS ANALOG CHORUS PEDALS
Many of the original analog chorus pedal designs relied heavily on the shifted delay circuits I mentioned earlier. Today’s digital delay pedals use a digital signal processor to split the signal, modulate the carrier wave, then combine it back with the original.
As results go, the two types of chorus pedals sound quite similar, and are less distinguished from one another, than something like a digital and analog delay.
However, digital chorus pedals — and digitized effects in general — offer a much wider range of control and manipulation, allowing us to more easily change the rate, depth, frequency and even the way the split signal is blended back together.
Modulation in Flanger Pedals
While not as widely used, the flanger effect follows similar script, splitting the input signal of the guitar, varying the carrier wave by adding a slight delay and then finally combining the two signals for output.
However, flangers do this by more rigidly controlling the placement of the notches created by the phased relationship, preventing them from being evenly spaced. It sounds like two large tape machines slowly sliding in an out of sync with one another, at a fixed speed.
This creates an effect that some would describe as a plane passing overhead.
This required a far more powerful IC chip, which didn’t become widely available until the late 1970s. Even then, it was super expensive and power-hungry, requiring a dedicated power supply to run.
THE LIMITATIONS OF FLANGER PEDALS
What has limited the use of flanger pedals is that it’s far more oppressive and intense than the other modulation-based effects.
A core strength of waveform modulation, particularly for the electric guitar player, is that it allows you to manipulate and thicken your signal without saturating the final output. The flanger effect has a harder time pulling this off, despite being structurally and technically similar to its chorus and phaser pedal cousins.
The simple act of matching up the notches in the phase cycle creates a very powerful, swirling effect, that doesn’t take long to wear out and tire the listener.
This is why it has seen sparing application from pros and amateur players alike.
FLANGER PEDAL USES
The hidden benefit here is that in some situations you might want a more intense modulation, in which case the flanger is a perfect solution. For example, I’ve found that the verse melody for Korn’s “Freak On a Leash” is handled really well by an intense flange effect with the Boss BF-3:
Here’s the audio sample:
https://www.guitarchalk.com/wp-content/uploads/2016/12/Freak-on-a-Leash-Riff-Sample.wav
In a more conventional sense, the flanger has — more or less — the same usage and application as the chorus. Simple layering and anywhere you need some clean signal flavor is a good place to start experimenting with a flanger pedal.
- As a low intensity layer of modulation
- As a covering for a clean electric guitar signal
- As a dimensional expansion for a clean bass signal
- For layering acoustic guitar lead melody and chord progressions
- Combining with distortion or delay for intense lead melodies
I added the fifth recommendation in light of the Korn example, since flangers tend to pair really well with delay and distortion for more intense lead tones.
For example, Billy Corgan used one in his heavily distorted solo on the “Cherub Rock” track.
A good flanger policy is to use it sparingly, but when you do bring it out, let it take over and do its job well.
Modulation in Phaser Pedals
While phasers are harder to understand in concrete terminology, the process is a familiar splitting and re-joining of the original guitar signal. During the split, a phaser pedal changes the waveform in multiple stages using what’s called an all-pass filter.
In an analog phaser pedal, this happens with physical filter stages, while a digital phaser pedal does this all in a single chip.
Once the two signals are re-joined, the result is a rippling, pulsing effect that sounds similar to the flanger, but quicker and less saturating.
The rejoining of the carrier signal to the original input is a mixture of in-phase and out-of-phase waves. Adjusting the ratio of these two components will change the speed of the effect which, in many analog phaser pedals, is the only tweakable feature.
Digital phaser pedals have the advantage of being able to artificially change the number of all-pass filters, giving you some added tweaking ability.
In an analog phaser pedal, this is not possible since each filter (usually eight or 12) is a physical component.
PHASER PEDAL USES
I like to think of the phaser as a much more subtle and nuanced flanger, where you can hear the swirling “meeting” of the in-phase and out-of-phase cycles, yet the saturation level seems much more manageable.
The phaser pedal can be dialed back to an extremely low intensity for simple layering, both for lead and rhythm uses. It found a particularly comfy home in the late ’90s and 2000s as a mainstay on nu-metal guitarists, adding flavor and variety to melodic verse riffs that would have sounded fairly small without the phase modulation applied.
It’s also a fixture in blues, funk and a popular choice among bass players.
The phaser job description can be the same as what I listed for the flanger:
- As a low intensity layer of modulation
- As a covering for a clean electric guitar signal
- As a dimensional expansion for a clean bass signal
- For layering acoustic guitar lead melody and chord progressions
- Combining with distortion or delay for intense lead melodies
Conclusion
It might be fair to say that this has all gotten deep into “guitar nerd” territory. Because you could certainly use any of these effects without understanding what modulation actually does. But, personally, I find it helpful to know how it works, especially if I’m to use them effectively in a recording environment or a live sound scenario.
If I’m going to throw modulation around like I know what it is, then I want to actually know about it.
What’s more, it doesn’t take too long to read through. Maybe 15 minutes?
Again, if you want to jump deeper into this topic — perhaps to research other types of effects — I highly recommend Dave Hunter’s book, Guitar Effects Pedals — The Practical Handbook. I referred to it a lot while researching this piece, and it has a ton of great information on the effects we use, including a thorough look at the history, technical complexities and uses of each type of effect.
Your Questions about Modulation & Effects
If you don’t want to buy the book, but you have more questions, I’d be happy to try and answer them here.
The comments section below is the best way to get in touch.
Leave your thoughts and questions there and I’ll answer pretty quickly.
REFERENCES AND WORKS CITED
- Zölzer, Udo; Amatriain, Xavier (2002). DAFX: Digital Audio Effects. John Wiley and Sons. p. 76.
- Hunter, D (2004). Guitar Effects Pedals: The Practical Handbook. Hal Leonard. p. 23.
- Noordhof, Jan. “How Does Modulation Work?” Tait Radio Academy, www.taitradioacademy.com/topic/how-does-modulation-work-1-1/.
