So Knee amount would be how much of an itchy trigger finger the goblin has then? 
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He actually controls the levels with a pedal. But heās got pretty bad arthritis. āKneeā literally just describes how itās feeling. If his knee feels hard, he can jam that pedal all day. But if itās rainy and his kneeās a little soft, he has to kind of ease into it.
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Love it!
This whole goblin in a box thing is giving me massive Pratchett (photo/video cameras work that way in his Discworld universe) vibes anyway and should be the primary explanation of all things technical to begin with.
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essentially in an optical compressor there is a special light that changes in intensity depending on the gain of the signal. A corresponding photoreceptor device detects this change in intensity and translates that optical change into a voltage change for the gain reduction circuitry.
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with responsiveness optical compressors are actually considered to be one of the āslowestā types of compressors. Compared to FET comps (1176) the attack time (which usually cannot be adjusted) on opticals is quite slow. The usual implication for opticals is on tracks that you want constant, smooth, compression that just kinda hangs in it compression zone and glues everything up. The ratios used are lowish (unless there not) for gluing and they they tend to have a hard time catching transients like percussions, so they are not ideal for making drums smackā¦obv these are not rules, but just kinda how it has traditionally been used (except the times it wasnāt)
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So what youāre saying is that optical compressors employ old goblins who canāt hear any more and are a bit too slow for regular work.
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I would have thought optical operated at the speed of light, and non-optical operated at the speed of goblin. Which is faster?
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It would seem that way! But essentially, while the light reaches the photodetector at the speed of light, the āreactionā time of the gain reduction circuit itself in response to said light is pretty slow. So I guess the goblin sees/hears just fine, but he was probably smoking happy cabbage on then job and as a result is a little slow on the reaction time 
Photo detection devices used in audio applications are a bit slow to react to change in light (transduce to voltage/ current) but theyāre really slow to ārecoverā, which is to say, slow to return to their nascent state. In a compressor this means both slower attack and release times.
There are several different types of photo detectors which all have slightly different characteristics wrt response/ recovery times and curves (linearity, etc) but theyāre all in the same general wheelhouse. I think āspongyā is a good adjective for their behavior.
This effect might be more noticeable in another common application which is the classic low pass gate circuit in west coast style synths where itās used in the form of a vactrol.
Iām sorry I donāt have a goblin analogy, Iām on my first cup of coffee.
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I prefer the goblin refs 
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@craig hates 303s
One Octatrack is not enough for @AdamJay
@DonovanDwyer loves white gear
@Fin25 is done with eurorack
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Tax breaks are involved iām told.
Goblins got a decent union, donāt they
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The walrus was Paul
the Paul was John
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He is the cats pajamas.
Thank you for the goblin!
perfect description
totally forgot about their use in vactrols! LPG applications are the perfect example of the spongy-ness (and thus ability to be used as a envelope) of how a photo detector behaves. Typically they make the action of anything they operate of really really smooth
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