Performer’s Ultimate Guide to Modulation FX Part 1

by | Dec 2, 2014 | Music Recording Plugins & Apps

We have a lot of guitarists who come through the studio and they have an idea what they want their recordings to sound like, but have no idea how to articulate those ideas in terms of effects we use in the studio. They may have a favorite song with that really awesome swirling sound on the lead guitar that makes the song ‘so epic!’ but they don’t really know what that effect is or how to explain it to us. Many guitarists do not really know the difference between Chorus or Flange or the best ways to apply them. In this article and in its second part, we will clarify the differences between various modulation effects and give some examples of these effects in practice so that you will be able to tell the difference going forward.


Right now you are probably asking yourself, what the heck is modulation anyway? Well to get super technical on you, the definition of modulation in terms of audio recording is the variation of an electromagnetic wave or signal, such as its amplitude, frequency or phase. Now that you are thoroughly scratching your head at that definition, let’s get into a more practical definition. All modulation effects are built around a Low Frequency Oscillator, more commonly referred to as just an LFO. An LFO is an audio signal usually less than 20Hz that creates a pulsating rhythm rather than an audible tone. These are used to manipulate synthesizer tones to create various modulation effects. There are a number of different effects that can be created from this and we will explore a few of them.


Two of the most commonly confused of the modulation effects are tremolo and vibrato. One reason for this confusion goes back to Fender mis-labeling what is now known as a “whammy bar” as “a tremolo bar” (when in fact it should have been called “a vibrato bar”). Tremolo modulates the amplitude of the incoming signal, resulting in periodic VOLUME changes, while vibrato is a modulation of periodic changes in PITCH. Both of these effects first came into fashion in the 1950s-1960s in the form of guitar add-on units (or pedals as we all like to refer to them now) and built-in amp effects.

One of the most famous and best examples of tremolo on a guitar track would be the opening guitar riff of the Rolling Stones song “Gimme Shelter.” In this song you can really hear the stutter effect that the tremolo is giving the guitar track. Another more modern example of tremolo on a guitar track would be the lead guitar part from the Black Key’s song “Howlin’ For You.” Or think of the opening to “How Soon Is Now?” by The Smiths.

In general, vibrato works well in short spurts, like using a whammy bar on a guitar for a short passage or bending a string up and down (vibrato) on the fretboard.  It’s hard to give an example of a song that uses a vibrato effect on a guitar track because, well, it doesn’t generally sound that good over long periods of time because it produces a very psychedelic effect.


The flange effect is created by mixing a recording with a slightly delayed copy of itself, whereby the length of the delay is constantly changing. Back in old’n tymes, this was achieved by recording the same sound to two tape machines, playing them back at the same time while pushing down lightly on one of the reels, which slowed down one channel. But luckily, thanks to the miracle of digital technology, we can just throw some plug-ins on our recorded tracks and get the same effect. This creates a smooth, swirling feel to a guitar track. We usually have depth and rate controls, as well. The depth controls how much of the delayed signal is added to the original, and the rate controls how fast it will change.

A great example of flange being used well on a guitar track would be on the opening rhythm guitar track of the Heart song “Baracuda.” You can really hear the swirling sound as the guitar is chugging away in that famous riff.


The chorus effect is very similar to flange and is often times confused for it by guitarists in the studio. This is pretty understandable as chorus is created in nearly the same way as flanging. The biggest difference between the two is that chorus uses a longer delay time, somewhere between 20-30ms compared to flange, which is 1-10ms. This difference in delay time causes chorus to affect the pitch of the track it is applied to. The longer delay times of chorus causes slight pitch bends and depending on the speed at which the delays are set, you can achieve either a slow spacey sound or a fast wobbly tone. Nirvana famously utilized the wobblier chorus sound on the guitars in “Come As You Are.”  If you are looking for the smooth, slower chorus sound, look to the guitar sound on the Boston hit “More Than a Feeling.” And pretty much any clean tone on Police LPs will have a signature chorus sound.

Editor’s note – come back next month for more in-depth analysis on modulation fx and how to use them in the studio. 


Zac Cataldo is a musician and owner/producer at Night Train Studios, a recording studio in Westford, MA. He is also co-owner of Black Cloud Productions, a music publishing company. Reach him at [email protected].

Brent Godin is a bassist/guitarist and engineer/producer at Night Train Studios. He is also a talent scout at Black Cloud Productions. Reach him at [email protected].