'Magic' of 1000

[Aleksey Vaneev]

kilroy, thanks for the information.

[Frippertronix]

kilroy, what's so special in variable-mu gain?

The way it preserves your mix, Aleksey. As you are aware, harmonic distortion is the principle "by product" of compression/limiting elements. The question is always, "How does one go about following the quickly fluctuating input signals of complex dynamic material, apply the necessary control/gain reduction/level to that material, and minimize any artifacts in the process of doing so." One solution was employing continuously re-biased, or "variable gain", vacuum tube elements to get smoother, less violent gain changes for the compression being performed.

The relatively well behaved nature of these gain elements makes them highly desirable for mastering compressor/limiters. The engineer has to work a bit harder to tear the mix totally apart.

There are those that claim a Manley Variable-mu in the right hands can get 10db of clean reduction on a typical pop mix. No wonder then, that these things are in every high profile mastering room.

Does optical compression do something similar?

[kilroy]

No. They are different. Good electro-optical gain element implementations are capable of some very nice compression/limiting, the LA-2A is a classic example, but nothing seems to beat the way variable-mu gain elements "stack" a complex signal in a well behaved, pleasing manner. This due to the fact that the variable gain is handled with a tube element. The "mu" in variable-mu is really nothing more than slang engineering jargon for "tube".

Anyway these tube elements have different "load and release" characteristics that, when artfully engineered into a compression/limiting environment, make for some lovely sounding dynamics texturing on complex material.

Another thing...optical gain elements are capable of greater attenuation than variable-mu designs. It is very difficult to get a variable-mu gain element to really smash and pump, nothing like you can with typical FET or VCA designs. The maximum gain reduction of variable-mu elements is in the range of 12-25 maybe 30db. Contrast that to the 35db reduction to be expected from an optical element...or more severe yet, up to 50db for a FET element like Urei used in their 1176, or a whopping 100db of available gain reduction from a VCA design like the dBX 1066.

It all comes down to how much you want to bend your sound, and how audible you want that bend to be.

[Frippertronix]

Looks like tubes win the tone wars again, but transistors also have their place. I think it's interesting how few people realize that tubes have outstanding hi-fi and studio processing applications. They're not just for snobby guitarists.