Compressors II


This article is copied via http://www.alpha-phase.com/ courtesy of Fraser Murray (@PhrasorOfficial). Thanks Phrasor for all the great compression lessons!

– Differences between analogue and Digital compressors.
– Lookahead & Sidechaining
– Limiting and compression
– Cool tricks!

Continuing on from my last post on compression, this one will look into the reasons to use the super-fast digital compressors and when to use the more gentle, warmer analogue versions. Both statements there are sweeping, take them with a pinch of salt.

Anything made in the real world i.e (not a plugin) will have discrete circuitry within it, which will color the sound to varying amounts depending on the design principle of the particular compressor.

Compression can be achieved in a number of ways. You can compress the top peaks of the sound, bringing the maximum volume down. This is “downward compression”

The opposite to this is achieved via “Parallel Compression” which is worthy of a post all of it’s own. The way parallel reduces dynamic range is from the bottom up, making it “Upward Compression”

Most compressors will offer differing modes which hint at what the compressor is to used for.

RMS (Average-sensing)
FET (Peak-sensing)
Opto (light-sensing)

RMS sensing compressors are the most common. They have the option of reacting fairly quickly if they are programmed correctly, whilst retaining the ability to be “invisible” at lower levels of compression. They pump less than Peak sensing compressors, but more than Opto compressors. Due to the utility of RMS compressors these are the “go-to” compressors in most engineer’s sonic arsenal.

Peak sensing compressors act fast. Very fast. These compressors are used where catching transients is of utmost importance. One might use this type of compression for catching loud transients on a vocal recording, fixing sibilance or smashing a snare drum hard.
Peak Limiters are also Peak sensing, hence the name.

Optoelectronic devices react to light by increasing or decreasing resistance, depending on how bright a lamp within the item is.
This brings inertia, non-linearity and pseudo-randomness to whatever it is being applied to. In our case, Opto compressors.

Due to the non linearity of the system, the “Attack” and “Release” parameters are much less accurate, and used more as a guideline. Opto compressors are generally incapable of very high ratios or quick attack times, so not too helpful for individuals drums etc.
Where opto-electronic compressors really shine, however, is being used on more delicate sources. Across the bus for a whole drum or vocal mix perhaps. I use them on plucked synth sounds to really round out the sound. The non-linear way that optoelectronic compressors work is similar to how the ear perceives volume differences, which makes the compression sound extremely natural and open.

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