This month we’re looking at two studio legends: the 1176LN Limiting Amplifier and Teletronix® LA-2A Leveling Amplifier compressors. Each one is quite different from the other. We’ve done articles and videos in the past showing how they work, but one little-known compression secret is that they can be used together on the same track. Why, you may well ask? Because it gives you more control over the compression and can create a very smooth effect, especially on a track that varies wildly in dynamics.
Sometimes you can’t reign in the dynamics the way you need to with one compressor without causing audible compression artifacts. For example, if you like the sound of getting 5 to 7 dB of compression with the LA-2A, a large peak might suddenly cause 12 dB of compression and the release might not recover in time for the next audio transient. You'll hear the level slowly come back up: your basic “pumping and breathing” effect. So using a fast compressor right before the LA-2A does the trick. Some people use three or more compressors on a track! One basic rule is that each successive compressor has a lower compression ratio than the one before it, and the first one is typically just catching the peaks.
To review the two compressors, the 1176LN Classic Limiting Amplifier is a FET-based compressor. It has Input and Output gain, Attack and Release controls, and four compression Ratios. It doesn’t have a threshold control, but turning up the input gain has the effect of turning down the threshold. Aside from that, it is very much like most utility compressors.
The LA-2A Classic Leveling Amplifier, on the other hand, is an opto-based compressor, which means it uses a electro-optical device to perform gain reduction. There are no attack, release, or compression ratio controls. There is Peak Reduction, which increases the amount of compression by lowering the threshold. The tube-driven output Gain control makes up for the gain lost by the peak reduction. Finally there is the Limit/Compress switch, which increases the compression ratio from around 3:1 (compress) to 10:1 (limit).
The most common combination is to put the 1176 first and set it up as a peak limiter. To do this, set a high compression ratio, like 12:1, and a fairly fast attack and release. The point here is to just flatten the higher peaks. This compressor should not be doing a whole lot, just knocking 2 to 3 dB off of the loudest peaks.
The input gain needs to be adjusted carefully to do this. Usually it is best to find a part of the track with the highest peak or peaks and cycle that, and adjust to get the effect I described. Then use the output gain to match the level. To do this, disable the compressor and listen to the average level of your track, then enable it and adjust the output gain until you can’t really hear a difference in level.
The LA-2A should be set up just like you would if it were being used alone, with the Compress/Limit switch set to Compress, and Gain Reduction and Gain set to taste. But the 1176 knocked the big peaks down, which would have thrown the LA-2A into quite a bit of compression.
You can also reverse the order of the two, using the LA-2A in Limit mode to knock down the peaks, and the 1176 to smooth out the rest of the track. Just like all audio tools, there are no hard and fast rules. If something has the desired effect, go for it!
Check out the video to see both of these compressors being used together on a variety of audio tracks.