Serial Compression, Simplified. (The 3 Biggest Reasons to “Stack” Your Compressors)

Like Parallel Compression, Serial Compression is one of those esoteric terms that pops up  from time to time and can leave newer producers and engineers scratching their heads. While the name might seem obscure, the process is anything but:

Serial processing is the act of using two or more of the same general type of processor on any given track.

“Putting one compressor before another is something that was going on long before it got a fancy name that made it sound like a ‘technique’,” says Joel Hamilton, one of the four accomplished audio engineers we asked to weigh in on the subject.

“But the idea that you can kind of mine different things out of the same signal by chaining devices with different tones or time constants is totally valid.”

Simply defined, Serial Processing is the use of two (or more) similar effects on the same audio track, one after the other. Most often, you’ll encounter the term as it refers to compression. But, intentional processing in series often occurs with EQ, de-essing, even time-based effects like reverb or delay, and more.

In addition to Hamilton [Tom Waits, Elvis Costello, Blakroc], we talked to producer/engineer John Agnello [Sonic Youth, Dinosaur Jr., Kurt Vile] as well as platinum mastering engineers Randy Merrill and Scott Hull of Masterdisk, about their approach.

WHY COMPRESS IN SERIES?

“It’s like using shellac,” Hamilton continued. “You can’t buy a bucket of shellac, pour the whole thing out on your tabletop and expect it to turn out extra-glossy. But, by applying it in a dozen tiny layers, one on top of the other, you can bring the surface to a really high shine.”

Joel Hamilton.

“Much the same way, you can’t compress 20db with a Neve 33609 and expect it to sound like several devices each pulling back a few db.”

All of our panelists agreed: sometimes, spreading the work across more than one compressor leads to better results:

“It’s well-known that in general, the shorter the signal path the better the sound quality,” said Scott Hull of Masterdisk [Miles Davis, Bruce Springsteen, The Ramones].

“While that’s true, and I’ll never use more gear than what’s needed to achieve the goal, you can’t always get what you need from one device. What you may need is the complex interaction between two. I would probably never choose to put two of the same compressors or EQs inline on the same track, but I will often use two different-sounding but similar types of processors if the combined result is better than without.”

When we boiled it down for this article, it became clear that our panelists consistently cited three basic reasons for stacking their effects: Tone, Tweak Points, and Timing.

REASON #1: TONE

“There are some pieces of gear that just have a great character and I’ll use them when that character is needed,” mastering engineer Scott Hull said.

“What might confuse engineers that use primarily digital processing, is that an analog EQ isn’t always an EQ. And an analog compressor isn’t always a compressor. Running through my compressors with no gain reduction sometimes produces very favorable results from a tone or color standpoint.”

John Agnello. Photo by Andrew Kesin.

Producer/engineer John Agnello agreed:

“I believe that when you’re in the analog world, different pieces of gear do sound different from each other, even if you’re just passing signal through them.”

“You can patch into a Pultec and it’ll sound completely different than an API 560 before you even do anything. Sometimes you don’t want to do a ton of EQ, but you want the sound of that piece of gear.”

REASON #2: TWEAKABILITY

“With a Pultec,” Agnello continued, “you might just add a little bit of low end or a little bit of top-end, and still get the sound you need from it. But you may still  want to sculpt it more, so you might go into an API 560 after that and notch out or notch in a bunch of frequencies.”

“So there’s the sound quality of each piece of gear, and then there’s also the practical factor of having access to all the frequencies you want to get to. You may want the sound of a Pultec but the flexibility of a graphic EQ.”

“I’ll do that a lot on snares and vocals. I’ll usually go through a 560, and then at the end of my chain I’ll have a nice fat Pultec, or maybe a Daking, just to give it a little size on the back end – just to take that sound and make it sound 10 percent bigger at the very end.”

“…you can’t always get what you need from one device.”

Hamilton’s thoughts were along the same lines: “There’s a difference between boosting 3k on a Neve 1084 and boosting 3k on an SSL EQ.”

“On an SSL, I know that frequency is going to hurt me a little. The same way, I might want to boost 8khz on a Pultec instead. So that way you can end up with a few EQs on the same source pretty quickly.”

Merrill had similar points to make: “I use multiple EQ’s in series a lot. The curve shapes and phase responses of each of my EQ’s is different.”

“I’ve found that in some cases, several small, incremental adjustments across multiple EQ’s gets me the sound I’m looking for, as opposed to adding more EQ on one unit in the same range. Other times this isn’t the case, and I’ll do a lot of EQ with one unit. It always depends on the mix, but I’d say more often than not, I’m using multiple EQ’s.”

REASON #3: TIMING

With compressors, there’s another crucial factor: attack and release times.

“When it comes to the ‘how’ part,” said Hull, “ I find it’s simply a matter of putting the compressors with longer attack times first in the chain and faster attack compressors and limiters later in the chain. This isn’t brain surgery.”

Scott Hull of Masterdisk

That kind of stacking was the first thought to come to mind for Agnello and Hamilton as well:

“As far as time constants, you could put on a very slow, low-ratio compressor first, and send that into a fast limiter that’s catching just the top of the peaks,” said Hamilton.

“That can make it feel like the track is plowing through molasses to get to the limiter. With that approach, you can take something that’s very lightweight and stringy, like an arpeggiated nylon-string guitar, and get some real heft out of it. It’s almost like adding a sense of inertia; some real weight in a mix.”

“It can help get rid of that really unencumbered and pointalistic sound that people associate with a straight up Pro Tools mix, where you have all these really spikey transients. For me, it could be a slower, gushier compressor first, like a Collins 26-1U, followed by a Neve 33609 set to a really fast attack and release.”

Agnello had a similar approach on electric guitars:

“A lot of times I’ll go with a tube compressor and put a solid state compressor on the back end, or vice versa, depending on what sounds I’m going for. If I’m having trouble getting a guitar to sit in a mix, I might put it through an LA-2A to give it a big tube action, but at the end put it through an 1176 and compress the sh*t out of it, to make it really like a brickwall.”

Of course, there are times when the opposite approach can work. When tracking an especially dynamic vocal or bass part, it can be advantageous to set up a compressor with a fast release time first in the chain. A busy and dynamic part can wreak havoc on a slowly responding compressor, allowing some peaks to go by uncompressed, while low-level parts of the performance wind up quieter still, buried in the trough of the compressor’s lazy recovery.

The classic example here would be taming a dynamic vocal with a quick tap from a fast-recovering 1176 before allowing it to pass through an LA-2A or Sta-Level set to deliver more consistent compression.

NEED FOR SPEED

Sometimes, two fast dynamic devices in a row can be handy:

According to Agnello: “If you have some nasty “S”s, sometimes one de-esser won’t do it. You’d have to hit it so hard that it’ll catch too much, giving you a lisping effect. I might give the S’s a little nudge with one de-esser, then really go for the kill with a second, trying to take out as much as I can. I like to think of it as setting up with one and knocking it down with the other.”

“I almost never use two compressors,” added mastering engineer Randy Merrill, “but I often use two limiters in series. I find at times that one particular limiter can only sound good up to a certain point. Once I get there, I’ll rely on another, different limiter to get me closer to the result I’m looking for.”

SETTING IT TO STUN

Unlike our mastering engineers Hull and Merrill, our mixers (Agnello and Hamilton and myself) felt that while stacking compressors can lead to greater transparency, that isn’t always the goal. One or more compressors in a mixer’s chain could very well be set to “stun”, ruthlessly lobbing more than a dozen db off an unsuspecting sound source.

Serial compression can still help in these cases as well. Feeding our “character compressor” a signal that’s already been cut down to a manageable dynamic range can ensure that our hardest-working box delivers an even and predictable effect, rather than jumping around in color and responsiveness due to an erratic signal.

EVERYTHING ELSE

Shane Stoneback discussed sending his plug-in reverbs to a real live chamber in our recent Cults interview. Hamilton is also a long-time proponent of searching for new sounds by stacking ambient effects:

Smile! You’re probably doing serial processing already without even thinking about it.

“In general, I really love reverbs layered up. I might have six reverbs on a mix,” he said. “I could be using a spring that doesn’t even go to the main mix – it could be there just to feed a plate reverb.”

“I guess what I’m looking for is a kind of ‘custom complexity’. If the album was tracked in hotels and bedrooms, I might want to create a unifying, Motown-ish kind of signature reverb that ties everything together – you know, where everything kind of lives in this one really unique space.”

For his part, Agnello remembers a time before multi-parameter reverbs. The earliest versions of these chains of time-based effects were patched in by guys like him, using a tape-slap delay to feed a plate reverb.

“Nowadays, the pre-delays are built-in,” he said. If you have an Eventide, you can just pull up anything you want – a flange into a plate – whatever.  Of course you can explore as much as you want. The only thing holding you back there is how much gear you have at your disposal and how much time you want to spend f*ing around.”

And Agnello has spent a lot of time doing just that:

“While working on my second Dinosaur Jr. record [Without A Sound] at Electric Lady, J [Masics] would want me to put one piece of gear after another on his guitar to hear what it would sound like. ‘Put something else on it, let’s see what that does. Ok, now something else’. We’d end up with these chains of like 5 boxes in a row. Sometimes it worked and sometimes it would be ridiculous.”

“But there would be those times where it would be amazing – all of a sudden the guitar was really jumping out of the mix. We just kept listening and trying until it sounded good. I don’t think we called it anything. We were just experimenting.”

Hamilton had similar feelings about attaching terms to the things we do instinctively:

“I think the name ‘Serial EQing’ only came about because of the proliferation of internet ding-dongs talking about Parallel EQing,” he said, as I tried to avoid looking sheepishly at my feet.

“But I guess we’re stuck with the term as much as we’re stuck with anonymous internet punditry.”

As long as that’s true, we’ll be here, hoping to undo the damage by bringing a bit of clarity to all the chatter.

Now go get in tune with your instincts, and start some experiments of your own.

Justin Colletti is a mastering engineer who writes and talks about music, sound and how we make it.

This post was originally published August 18, 2011. We have updated and republished it to help our newer readers.

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