chorus, distortion, double chorus, modulation, TZF, unitard -

Secrets of tone: What makes the DoubleChorus so epically rad

You remember the '80s, dontcha?

Big hair, overstated eye-makeup, leopard print, mountains of blow, cheap groupies, and who could forget the image that has been burned into a minds and psyche (for better or worse):  painted-on hot pink unitards with what looks to be a malformed potato bursting from the nether-regions of the lucky guy who shoe-horned himself into that unitard.

Lets not forget one of the most popular (and new for the time) effects of the '80s:  the chorus tone.

This edition of Straight Jive will cover a little about the chorus sound, but most of all, we're gonna focus on exactly why the Double Chorus is the ultimate shit, why it sounds so much better than most every other chorus pedal you've played and how a guy who doesn't like chorus (like myself) can get down and boogie in his own personal unitard:  a beat up pair of Levis.

Your standard chorus sound is produced through a relatively simple process...

A signal (your guitar in this case) enters the effect circuit and immediately encounters a short delay line.  But this isn't any ol delay line.  This delay line is special, like the finest columbian money can buy.  Because unlike a big ol pile of blow, its modulated.  What does that mean exactly?

What the effect will be doing is modulating the delay time, meaning that the time delay, td as we'll be referring to from this point forth, is continually changing: much like a rockstar's evening groupie.

The modulated delay is added to the un-adulterated signal (dry signal) replicating the sound that occurs when two people play guitar at the same time.  Super neat!  Now one rockstar sounds like two!!  And what's better than two rockstars?

Two rockstars with four groupies.

Check out the picture below to get a visual on the action:

The brown line is our dry signal, occurring at td = 0S (real time).
tdThe blue line is our modulated delay line, centralizing around td = 0.01S (10mS delay).
Note as time goes forward (moving to the right along the X axis, the modulated delay line's td is changing.
When we mix these two signals together (literally combining the signals by adding them to each other) we get our basic chorus sound.  Pretty easy, right?

So why does regular chorus sound so corny and boring?

The corny part is simple really.  Everyone in the '80s wanted that amazing new tone.  So everyone used it.  Of course, that made the chorus sound a pretty iconic tone of the '80s, and all the corn-ball shit that went along with it (see the list in the first paragraph).

The boring part is where things get interesting (deep, man. deep).  With only one modulated delay line, our ears can actually tune into the modulation that is occurring on the wet (modulated delay) signal and as a result, we hear the pitch change independent of the dry signal.


Let's get one thing straight:  chorus doesn't suck.  Plain-jane chorus sucks.

Then why is the DoubleChorus so fucking epic?

And this my friend, is where things get rad.  Epically rad.

The DoubleChorus is called the DoubleChorus for good fucking reason.  Its not just a chorus pedal.


The heart of the Double Chorus is its chorus "engine" so to speak-- what is actually making the chorus, and how this super-mega-plus-plus-super-whammy-bagels portion of the circuit works.

While most chorus pedals combine a modulated delayed signal with a non-delayed signal, the Double Chorus combines two inversely modulated delay signals with each other, twice.  Then mixes in as much of the dry signal as you want.  From 100% dry / 0% wet to 0% dry / 100% wet.  Right smack dab in the center of this (50% dry, 50% wet) you get a complex, massive and smooth chorus sound, without the typical warble and predictability to get from single delay line chorus.

Sound a little different?  It is.  And there's more.

We'll be referencing a little bit of trig terminology for the next section, but that's just the nomenclature.  If the words confuse you, the pictures will make it easy.

The heart of the DoubleChorus

Remember how the Double Chorus "combines two inversely modulated delay signals with each other, twice?"  Here's an illustration detailing how it all works and why the Double Chorus sounds so goddamned tight.

Lots of shit going on, eh?  Its really not as complex as it looks, but some careful examination will help break it down for ya.

Lets start by looking at the blue lines, herein referred to as "Chorus Pair 1":

You probably first noted that they are "opposite" one another, that is to say:  when one goes up, the other goes down and vice versa.  Well, you're spot on and for the trigonometrically inclined, we'll make some simple equations for those two lines: Sin(x) and -Sin(x) respectively.  You see how this works now?

But there's a neat little detail that's not being shown in this simple two-axis illustration:  the relative phase of each line (signal).  See, if both signals were in phase with one another, we'd have some neat chorusing and vibrato happening, but it wouldn't be epic.  It'd be a hair past regular, and frankly, Mr. Black pedals aren't "regular."

The two signals forming Chorus Pair 1 are actually 180° out of phase from one another, which means when they meet up (paths cross) they fully cancel each other out.  ...kinda like a through-zero flanger...  For a refresher on this process, dig this Straight Jive article.

So that's all neat and dandy, but what about when they're as far away from one another as possible (both waves at their "peaks" so to speak)?

Well, the short answer is: we have effectively created a "chorus effect" with two modulated delay lines rather than one.  A "double" chorus, if you will; and even if you won't.  That's pretty cool, but remember that twice caveat from "combines two inversely modulated delay signals with each other, twice?"

Here's where we get down to the itty-bitty-nitty-gritty-ditty-boo.

Remember the first picture in this series?  Don't scroll!  Here it is again:

We've added two more modulated delay lines ("Chorus Pair 2") and we can make some simple equations for those as well:  how bout Cos(x) and -Cos(x)?  Awww yeah.  Now you're starting to see it.

See, Sine and Cosine are quite closely related to one another.  In fact, they are essentially the same, with a 90° phase shift occurring between the two.

So we can say, for our purposes at least, that Cos(x) is 90° out from Sin(x).  We can then infer that -Sin(x) is 90° out from Cos(x), since -Sin(x) is 180° out from Sin(x).  We then can conclude that -Cos(x) is 90° out from -Sin(x), since -Cos(x) is 180° out from Cos(x), and thus -Cos(x) is 270° out from Sin(x).  Isn't deductive logic fun?

What all this crazy shit means is that we have both a peak (high point of a wave) and a valley (low point of a wave) occurring every 90° (at 0°, 90°, 180° and 270°), which means we have two complementary waves (180° out of phase from one another) canceling each other out every 90° (at 0°, 90°, 180° and 270°), and thus we have two identical waves summing every 90°, after a 45° shift (thus at 45°, 135°, 225° and 315°).  Confused yet?

Its a lot of numbers, degrees and shit to keep track of, but here's the breakdown of what your ears will hear from the delay lines during one complete cycle (phase angle represented with our good buddy theta, θ):

Phase Angle ( θ = ...  )
θ = 0° Subtractive TZF
0° < θ < 45° Chorus
θ = 45° Additive TZF
45° < θ < 90° Chorus
θ = 90° Subtractive TZF
90° < θ < 135° Chorus
θ = 135° Additive TZF
135° < θ < 180° Chorus
θ = 180° Subtractive TZF 
180° < θ < 225° Chorus
θ = 225° Additive TZF
225° < θ < 270° Chorus
θ = 270° Subtractive TZF
270° < θ < 315° Chorus
θ = 315° Additive TZF
315° < θ < 0° Chorus

Pretty rad pattern we see forming, huh?  And that's before we mix in the dry signal!

Well shit.  That looks fucking amazing already!!  So why include any dry signal at all, let alone a full wet/dry mix control?

Why its very simple really and I think I can break it down for you in just one big, long, silly run-on sentence:

If all dry has no chorus effect and all wet is crazy four-line-super-mega-TZF-ultra-plus-plus-dyna-boom-boom-chorus, then it stands to reason that you can cop a ton of new and amazing tones by gaining full control of the ratio of dry to wet.

And that is why you get a full wet/dry mix control on every DoubleChorus.  Shouldn't ALL chorus pedals have this control?

Okay then.  Then why does the DoubleChorus work so well with distortion?

Well that's a pretty simple question as well.  Privately funded research studies show that single delay line chorus circuits can sound really... um... cheesy when run after distortion,  be it in pedal or amp form.  Multiple delay line chorus circuits completely circumvent the cheese-ball factor by fooling your ears into never hearing the movement of the individual delay lines.  Its an aural-illusion so to speak, and one that sounds really, really good.  So good, you'll never look at the chorus effect the same again.

And that, my friends, is why the DoubleChorus is so much more than just another chorus pedal.

Now go forward and fear no unitard!