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February 3, 2020

LA-2A emphasis | F. Reid Shippen




The Emphasis knob on the legendary LA-2A compressor/limiter is something you don’t hear discussed too often. But the focus on in this excerpt from the Puremix video, “F. Reid Shippen Mixes Ingrid Michaelson.” Reid demonstrates how it works when compressing vocals on the song “Afterlife,” and he remarks that adjusting the Emphasis knob can change the character of the vocal.

Before we get into what Reid does in the excerpt, here’s a quick refresher on the other key controls on the LA-2A, because they’re somewhat different than on a typical compressor. There’s no ratio control; the unit has a fixed ratio of about 3:1. The Peak Reduction knob is essentially the threshold control. Turning it clockwise lowers the threshold, thus increases the amount of compression. Unlike on an 1176, the Gain control has no impact on how much compression you get. Now, let’s look at the Emphasis knob.

The LA-2A’s Emphasis knob is perhaps the unit’s least-understood feature.

You’ll notice that Reid is using a UAD Teletronix LA-2 plug-in, in the video. The original hardware LA-2 was the version in between the LA-1 and the LA-2A. The LA-2A had more efficient wiring and a lower noise floor, and it also added the Limit/Compress toggle switch, but the overall functionality of the LA-2 and LA-2A was mostly the same. The “LA” in the name stands for “Leveling Amplifier.”

Emphatically So

In the excerpt, you see Reid adjusting both the Peak Reduction (Threshold) and Emphasis knobs as the vocal is playing back. At one point, he has the Peak Reduction set quite high, at about 80, increasing the compression quite a bit. He also has the Emphasis knob at about 11 o’clock. Then, when he turns it to its default 5 o’clock position, the vocal level drops significantly. When he turns it back counterclockwise, it gets louder again.

With the Peak Reduction this high, Reid gets a lot of compression with the Emphasis knob in its default position.

That makes perfect sense once you understand what the Emphasis knob is doing. It’s adjusting a filter in the sidechain input to the compressor—that’s the input going to the compressor’s detector circuit. When the Emphasis knob is in the default position, the full frequency range of the incoming signal triggers the compressor. As you turn it counterclockwise, however, it starts filtering out the low-end from the sidechain.

By the time you turn it fully counterclockwise, the detector is triggered mainly by high frequencies. Keep in mind that bass frequencies have more energy and trigger a compressor more heavily, so turning the Emphasis counterclockwise—which is filtering out progressively more bass—results in less compression.

Filtered Audio

Let’s get back to why the vocal dropped so much in level when Reid turned up the Emphasis control. He had the Peak Reduction way up, but initially, the Emphasis knob was set a little to the right of 12 o’clock. As a result, the circuit was filtering out much of the low frequencies, and the compressor wasn’t getting hit too hard.

Then, when he turned the knob back to its default, all of a sudden the detector was responding to all frequencies, and it instantly started attenuating more heavily. Watch the gain reduction meter when the vocal level drops—it goes way up. When you add those bass frequencies back in, you get more compression.

Some compressors, such as FabFilter Pro C-2, have a built-in sidechain filter, which works similarly to the Emphasis knob in the LA-2A.


As that example showed, the Emphasis knob can have a significant impact on the signal level; if you have the Gain Reduction turned up high. But if you have it at a lower setting, then the effect will be more subtle and can be a “character changer,” as Reid pointed out. That’s because the compression is getting triggered by different parts of the signal, which alters how it affects the track.

The Emphasis control operates similarly to a compressor with a built-in sidechain filter. You’re limiting the frequencies that are going into the detector, thus affecting the amount of attenuation that occurs.

Reid showed how changing the Emphasis feature affected the sound of a vocal. Let’s check it out on some other instruments.

Example 1 features the LA-2 inserted on a drum kit. Because of the full frequency range between the kick and hi-hat, the position of the Emphasis control has a significant impact on the result.

Ex. 1: This four-measure drum part plays three times. The first time, the LA-2 is bypassed. When it repeats., with the Peak Reduction at a very high setting (80) and the Emphasis in its default, fully clockwise position. In the final four, the Emphasis is turned counterclockwise to about 10 o’clock, and the compression is less obvious, particularly on the snare, but is still gluing the drums together nicely.

The setting for the third time through of the part in Example 1, with the Emphasis at 10 o’clock.

Ex 2: This example features a picked Fender P-Bass. The four-measure section, which also includes drums, plays three times. The LA-2 is inserted on the bass track only. The first time there’s no compression. When it repeats, the Peak Reduction is set at a little over 60 and the Emphasis in its default position, and the bass is getting pretty heavily compressed. The third time the Emphasis changes to about 1 o’clock and the compression is a lot lighter.

The setting for the second time through of the part in Example 2, with the Emphasis in its fully clockwise, default position.

An effective way to adjust the Emphasis control is simply to play your track and turn the knob slowly counterclockwise from the default. You’ll hear the compression changing, and you can feel what works best. It’s probably best to do that with your other tracks on, so you’re not making that adjustment out of context.