The Logic Off Topic list

Mark Lennox wrote:

>I need someone to set me straight on Variable Mu compressors at a detailed 
>level.
<snip>
>Can anyone point me to where I might find info online or elsewhere? I need 
>to know this as I am trying to write a Variable Mu VST compressor.

Well ... I don't know if anything I say will "set you straight", but I'm 
willing to try to offer you the very little I know if it's any good.

As marc lindahl said, mu is basically just the term used by the tube-loving 
audio fraternity for 'gain'. The term 'Variable Mu Compressor' became 
famous because that's basically what Manley called their gear. The more 
general, and so probably more accurate, name is "variable gain compressor" 
or "vari-gain compressor". However, the Manley stuff is so famous that 
everyone pretty much thinks that the name they trademarked for their 
compressor is what all such compressors are called. Bit like Polaroid or 
Biro, I guess.

There's five basic kinds of gain reduction used by compressors:
1) Optical isolators using LED's, photoelectric cells and the like
2) FET's (field-effect-transistors) which use transistors
3) VCA's (voltage controlled amplifier)
4) Digital compressors (e.g. plug-ins)
5) Variable gains

Variable gain is pretty much a catch all in that it covers those 
compressors that include specific circuits incorporating specific 
electrical/electronic components that do not belong to the other categories.

If you're building a VST compressor then YOU probably don't need to know 
any of this, but for those who want the gen on compression here's a 15-page 
article which should set them straight:
http://www.digitalprosound.com/cgi-bin/getframeletter.cgi?/2001/02_feb/features/big_squeeze/big_squeeze1.htm

And ... since you're trying to build one then here's a longish pdf file 
which will probably really fascinate YOU but pretty much give everyone else 
insomnia!!
http://www.geofex.com/PCB_layouts/d&rpub.pdf

Here's the real McCoy ... the Manley site where there's lots of stuff about 
that really famous Manley Stereo Variable Mu Compressor. Yippeeeee!!
http://www.manleylabs.com/containerpages/mu99.html
Long time since I looked at it and it might well be where I got some of the 
links I've given above. If so, sorry for the repetition.

Then finally (BIG YAWN) here's some graphs taken direct off the Manley site 
that tells you what you really want to know 'cause it's some really dinky 
actual real life graphs showing relative gains 'n' stuff. Enjoy. And ... 
see how I really enjoyed keeping the good stuff until close to the end!!!
http://www.manleylabs.com/PDF/PRO_Manuals/Var%20Mu/gr%20chart.pdf

Hope I've helped you some.
Helpful is what I generally try to be, to be honest ... but ... best not 
say any more, ay??!!!!!!

Kool Musick
Keep Musick Kool


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