It's ironic that the compression technology that's perhaps the most difficult to wrap your head around — the fabled T4 opto-electrical mechanism that drives the Teletronix LA-2A Leveling Amplifier — is also the easiest to operate. Virtually anyone with ears can manipulate the LA-2A's ultra-simple two main control knobs — Gain and Peak Reduction — to bring signals under control with consistency and punch. But the new the LA-2A Classic Leveler Plug-In Collection adds some unique "under the hood" features and variation between the LA-2A plug-in models that may not be immediately obvious at first listen. Read on.

The Teletronix LA-2A Classic Leveler Collection includes units from three
different LA-2A eras — Gray, Silver, and the original LA-2.

The LA-2A Collection – Three Different Flavors

The Teletronix LA-2A Classic Leveler Collection includes units from three different LA-2A eras — Gray, Silver, and the original LA-2. Here's a simple breakdown. 

  • The UREI-built Silver LA-2A is generally appreciated for its faster time constant and its treatment of transients. This makes it a versatile performer that's suitable for the widest variety of applications — including drums, percussion, and bass guitar.
  • The Gray model, paying homage to Jim Lawrence's original mid-‘60s Pasadena-built units, is typically used for material requiring a medium-speed compression — think lead and background vocals, keyboards, and (judiciously) acoustic and electric guitars. 
  • The LA-2 model captures the mojo of one of the very earliest Teletronix units, offering the slowest response time and a distinctive "mellow" sound owing to its 50-year-old luminescent panel. It may be best used on legato vocals, strings, and horns. But you know the old maxim, “If it sounds good, it is good!”

Dialing in the Perfect Compression

The LA-2A's proprietary T4 photocell essentially works on a fairly simple principle. As the input signal increases, the light panel in the T4 cell gets brighter. As the light gets brighter, the photo resistor's impedance increases, which reduces the gain. As the input level decreases, the light dims and the resistor's impedance decreases. For the recording engineer, accessing this little trick of the light couldn't be easier. The LA-2A front panel boasts only two main knobs: Gain (this refers to its up to +40dB of output gain or “make-up gain”) and Peak Reduction, which on other compressors might be called “Threshold.”

Compression settings for the lead vocal, with the LA-2A Silver.

In a typical scenario, one simply inserts an instance of the LA-2A into a channel strip with the channel fader at unity gain, sets the Gain Reduction to tame the peaks and transients sufficiently, and then adjusts Gain to bring the new, more consistent signal level back to the desired place in the mix. I've done this in this example using an isolated vocal track and the Silver LA-2A. Keep your eyes on the gain reduction meter (which you can set to either display gain reduction, or output gain with a metering reference of -4dB or -10dB) to see how often the peak reduction kicks in, and use your ears to tell you if that makes for a natural sound or an overly squashed one. (Both can be effective; it's your call.)

Here's the lead vocal track before treating it with LA-2A compression:


Using Ross Hogarth's “Lead Vocal” preset as my starting point, I hit the Silver LA-2A compressor pretty hard here, with a high Peak Reduction and Gain at 50%, as I felt my original vocal sounded somewhat harsh. I used the Gain to help it inch up in my mix. Using my channel Send, I also blended another instance of the LA-2A Silver to add just a touch of even more aggressive compression. To further shape the sound, I've added some EQ after the compressor (though you can certainly place it beforehand) to bring out some of the high-mids I felt I may have lost, and to roll off a bit of low end. The sound is anything but “pristine,” but I like the body and warmth of it. Sounds like tubes to me...


For the Gray LA-2A, Bass guitar is a natural. Let's take a listen to this Fender jazz bassline before compression:


And here's the same Fender bassline processed with a low-medium Threshold, and Gain at about 40% to add some of that nice LA-2A distortion and warmth.


Though the simple controls of the LA-2A are great, you may be wondering why there aren't Ratio, Attack, or Release controls. Those values, which are so intrinsic to the sonic character of the unit, are actually fixed. The average compression ratio is always set at roughly 3:1, while the average Attack time is 10 milliseconds, and the Release time is about 60 milliseconds for 50% of the release, and anywhere from 1 to 15 seconds for the rest. Remember, this is a program and frequency dependent compressor, so it reacts a little differently depending on what goes into it. If you prefer a little unpredictability in your mixes, that can be a good thing. If you're an addictive knob twiddler, though, have no fear — the LA-2A has several other features that allow you to add expression to its ingeniously simple design.

Utilizing the Emphasis Control

The LA-2A's R37 Emphasis control — that “set-screw” knob on the lower left of the front panel — controls a shelf filter circuit in the compressor's sidechain input for frequency-dependent compression.

Emphasis is handy for emphasizing
compression on higher frequencies.

When the control is fully clockwise in the default position, the sidechain signal is unfiltered and all frequencies in the source signal that exceed the compression threshold will trigger gain reduction equally.

Rotating the Emphasis control counter-clockwise increases filtering of the sidechain signal. The Emphasis filter gradually reduces the lower frequency content of the sidechain signal, resulting in compression that is less sensitive to those frequencies, and more sensitive to high frequency content. As the sidechain filtering is increased, higher frequencies are compressed more.

You can think of the sidechain as the compressor's scolding big brother — the sidechain tells the compressor how it should behave respective to the incoming material, and it helps shape that material for processing.

Here's a drum track before treating it with the LA-2A Silver:


I've chosen to use the Emphasis control at its furthest counter-clockwise setting to help accentuate the “thwack” of a snare drum in a stereo drum mix. The snare wasn't quite sitting where I wanted it, while my kick drum seemed quite present, so a bit of Emphasis didn't lose me any significant lows, but it did help round out my mid-rangey snare drum with a little extra punch.

The New York Parallel Compression Technique

Nothing screams Big Apple like a little parallel compression, also known fondly as “New York” compression, thanks to its birth among a small coterie of Manhattan-based engineers. Typically, a compressor like the LA-2A is always going to be used as a channel insert — after all, compression is a dynamics processor, not an “effect” per se, and it has traditionally been used to allow maximum control over the individual volume levels of mono instruments.

The “New York” compression technique takes another approach, typically sending one or more stereo mixes of the drums to separate bus channels, compressing one bus channel conservatively, and the other very aggressively, then adjusting the levels of those channels to taste. This method retains the highly dynamic quality of the less compressed material while judiciously adding the color and dynamics of the heavily compressed signal, often at exaggerated levels that might sound inappropriate if applied directly to the source. Some engineers may send less overhead and cymbals to the more aggressively compressed bus channel in order to diminish excessive high-end noise.

This will impact your drum balance, of course, so you may need to play with the respective channels' compressor settings until you find the right blend, as I've attempted to do in the following drum part. Note how much more aggressive this one is than the very same part in the previous drum example, with only a moderate Insert compressor with Emphasis.

A Few More Examples

Here are a few more examples of how the LA-2A sounds on instruments. It's legendary for use on pianos and helps bring out the tube warmth of many vintage guitar amps, too.

Here's an example of a British Combo rhythm guitar line, first dry:


And here it is with moderate compression from the LA-2A Gray:


Here's an example of an acoustic piano, first without compression...


...then with the “JJ Bright Piano Warmth” present for the LA-2:


While most engineers will argue that the LA-2A is a distinctive flavor best used on highly dynamic “live-sounding” material, you may find uses for it that go well beyond its traditional settings. With three different flavors in the LA-2A Collection, the sky's the limit. Give it a try for yourself, and feel free share some of your own tips in the comments section below with other LA-2A afficionados.