Ah, the 80's. Was there ever a more glorious era of over-processed, over-wrought guitar sounds? If the 60's had the wah-pedal and the 70's had the phaser, surely the 80's was the decade of the chorus pedal. It was like the Sriracha of guitar effects—there were almost no tones that couldn't be improved with a little dose of chorus.
But over the years I've always struggled with getting a chorus effect to sound like the records I heard and, more importantly, to get it sit right in a band context or in a recorded mix. Have you ever set up a killer chorus sound (especially in stereo) only to find it lacks something when mixed with other instruments?
For me what was so frustrating was how it "sort of" sounded like what I heard on other records but not in any consistent way. How could this pedal that I know everyone is using give me such varied results?
The answer was that much of the time what I heard wasn't chorus but, in fact, pitch shifting.
The Chorus Effect
Let's step back a bit first and talk about what a chorus effect actually does. The "chorus effect" is what we perceive when multiple voices execute the same program material but with subtle differences from one another. In a choir the different timbres of each singer's voice are what make our brains perceive that there are multiple people singing and not just multiple exact copies of the same singer (that would simply just be louder).
A chorus pedal (or rack effect, or plugin) simulates the same effect by making a copy of the original dry signal and mucking with it in some fashion. The most common implementation applies some form of pitch-shifting to the copied signal(s) and then oscillates the amount of pitching shifting using a thingie called a low-frequency oscillator (LFO).
The electronics behind how a LFO works aren't important here, so just understand that the "rate" and "depth" controls on your pedal affect how the LFO works. A LFO modulates (changes) a signal on a regular basis, like a smooth wave going up and down. The rate control affects how fast the cycle is and depth affects how big the waves are.
If you set both to really high values you get the "gargling gnome" novelty effect. If you set both to low values you get a very subtle thickening of the sound and in between are all the other variations. Here are a variety of sound samples with different chorus settings:
Pitch-shifting is the process of tweaking the fundamental tone of a note by some amount. Effects like Eventide's PitchFactor (derived from Eventide's famous Harmonizer) have the ability to shift pitches by wide amounts so that you can play harmonized lines (e.g. a third above). But that's not what we're talking about here. When most people talk about "pitch-shifting" they're talking about moving the effected voice by just a few cents in either direction.
This is what makes a 12-string guitar sound different from a 6-string guitar. The top six strings are pairs of the same pitch and since it's very unlikely that they're exactly in tune the subtle pitch differences are what give the 12-string its unique chorused effect.
This means that a chorus pedal is essentially a pitch-shifter that varies the detuning effect over time. It was this cyclical variation, thanks to the LFO, that turned out to be the root of my frustration. Why did a chorus pedal sound so inconsistent to me? The answer was simple: because it was changing all the time.
As a result of the pitch-shifting being an always-moving target, the harmonic content of my guitar tone was also ever-changing. If we could make a note sustain infinitely on a guitar (maybe with an E-Bow or Sustainiac) and we looked at how the signal played out on EQ analysis, we would expect the frequencies to fairly steady. But when we apply a chorus to the same signal, the frequency distribution is constantly moving.
So think about mixing a chorused guitar part in with other instruments. If its EQ profile is always moving it's much harder to dial the tone into a specific tonal "pocket". The more pronounced the effect the wider the variation you have to deal with.
In contrast, a non-modulated pitch-shifting effect doesn't have the same wild variation. It provides much of the same "thickening" that a chorus effect does, but without complex variation that can be problematic. This is why 5150-era Van Halen tones never sounded right to me when I tried use a chorus pedal. But with a subtle pitch-shifting effect it sounds much like the original recordings.
Let's put this in more concrete terms with a head-to-head comparison. When David Lee Roth was replaced by Sammy Hagar and version 2.0 of Van Halen was launched with the 5150 album, Eddie revealed markedly different sound from the famous "brown sound" of the first five records.
For years I always assumed it was some kind of chorus effect, but after going back and re-reading old interviews with The Man, I'm pretty sure it was a rack-based chorus effect. This first sample is a grab bag of bits from the song 5150 played with chorus:
Here's the same guitar part but with the pitch-shifting effect replacing the chorus:
Tonally, these two samples sound different to me. The pitch-shifted effect is a little brighter, and maybe a little "fizzier" sounding. The chorused sample seems somewhat more mellow, especially in the upper-range frequencies. I've often found that when a chorused guitar part sounds buried no matter how loud I turn it up, that replacing it with pitch-shifting cuts through much better with less volume.
Now all of this isn't to say that the chorus effect is totally worthless. I quite like the chorus effect for certain sounds. But it highlights the importance of understanding the different effects available in your arsenal. Chorus and pitch-shifting sound enough alike that it's easy to conflate the two, but as we've discussed here they have important (though subtle) differences.
So next time you reach for a "chorus" sound and just doesn't sound quite right, consider a simpler pitch-shifting effect instead.