QuoteAutomatic gain control... Would that be a noise gate?

No an AGC tries to keep a constant output when the input varies - for example if you want to keep a mic to keep a constant output level on the PA regardless of how loud someone speaks, or where they hold the mic.

You might be getting the wrong impression from those app notes about the noise gate function.  The noise gate is not just a noise gate it's actually an expander first but with a noise gate function thrown in *with the expander*.   This is done by making the expander mistrack at low levels.

If you have a compressor then feed this into an mistracking expander you get a noise gate without the overall expansion function but it requires two stages and it's kind of a crappy implementation.

What you want is a fixed gain at high levels and a lower gain at low levels - that doesn't quite fit in with the circuits in the app notes.

Ah. :lol: damn

Quote from: NasseOne of circuits that I have lost is one nice stereo compressor article in some european or american electronic mag. The chip was 570 or 571, the project was named "CD compressor"  or "Australian..." or something thereabouts and the author had designed the project for reducing cd ´s dynamic range suitable for recordin to casette tape with less dynamic range. There was very good looking pcb, no exotic components and specs were good. I thought that would be nice compressor for home studio for multi synth or tape or computer track mixdown. The designer was from Australia. I have lost that magazine  

Hi Nasse,
That was an article called "Compressor for Compact Disks" that first appeared in "Electronics Australia" in the May 1986 edition, by Colin Dawson.  I saw it in a short-lived Canadian magazine called "Hands-On Electronics" -  the article appeared in the January 1987 edition.  And the chip was an NE572.

I built one channel of the compressor to use for guitar and used the other half of the NE572 as a noise gate.  Both operated independently.  As far as I can remember the compressor worked quite well and I modified the circuit to make use of the adjustable attack and release times (the original circuit had these optimized and fixed for audio hi-fi signals). Can't remember what happened with the noise gate part....

Given time and a few beers I could scan the article for you.  I may even be able to find my original circuit but don't hold yer breath, I have to wade through mountains of my wife's spinning and weaving equipment to get to the boxes where it may be stored.

Cheers,

Peter

Wow, thats a nice offer

Dont know what I can do for you, but maybe something pops up. I still have not access to good scanner, but maybe it changes soon. Take your time, no hurry, I dont worry but just remembered it was nice article.

Hi Nasse,

Send me your email address.

psnow@magma.ca

Thanks,

Peter

Hi Nasse,

I have scanned the article, if you want it.

Peter

Sure, did you receive my e-mail address. I owe you some beers, cheers, or I should offer you a bottle of Koskenkorva.

Hey peter, mind sending that article to smoguzbenjamin@hotmail.com?

And how about sending a copy to me? Email edguidry@lafourche.com. I have an extra chip, and I want to make a compressor for my acoustic.
Thanks.

Hey, what about me?
munkydiy@hotmail.com

Peter:

Please count me in as well:

d<NOSPAM>mcevoyATvoyager.net

You can probably guess what to do with <NOSPAM>.  Also what to convert AT to.  Sorry, I just don't need any more spam!  The 'bots seem to be all over the place!

Don't worry Dave, no bots here as far as I know.

Count me in also!!!
Thanks!
Arn C.

arn.conklin@ametek.com

I have a copy of the 570-Noise-Gate article from E&MM that RG sent me years back.  I can scan that and post it.  Hell, I think I even know where it is!

And yes, 570=571 for the most part, with 570's reputedly being better in the noise department.  Like most chips, though, I imagine that evaluating the noise-level differences is a function of the context in which you evaluate it.  I expect there will be applications where there is no earthly difference with respect to noise.  Note that the NE572 is an entirely different chip.  It IS a compander but it is not simply "one better" (as Nigel Tufnel would say).

Although compander chips can function as noise gates, the chief difficulty with them is that the time constants (attack/decay) are set by a single cap.  A noise gate that has minimal flutter/stutter and captures the initial attack of the note needs a fast attack and slow decay.  The single-cap aspect means you get fast decay with fast attack and slow attack with long decay.  I suppose there are compromises that can work, and settings that work terrific for somebody, but ultimately having the rectifier buried deep in the bowels of the chip makes it less tweakable.

Mark, if you could give me that article that would be the best late X-mas present ever!

I just checked the spec's of 570/571. Very small differences, noise figures are the same. The only significant diff is 570 max supply voltage = 24V, 571 = 18V.
Kindest regards, Bernt.

:oops:

Quote from: NasseSure, did you receive my e-mail address. I owe you some beers, cheers, or I should offer you a bottle of Koskenkorva.

Nasse,

Sorry, I did not get your email.  Can you try again please?  Or if you're worried about spam maybe post your email address here with changed characters like AT instead of @, like someone else has done.

Thanks,

Peter

I have emailed the article with the following exceptions:

smoguzbenjamin@hotmail.com  All 5 pages was too big, so I re-sent just the page with the schem.

Nasse - no email address yet!

Dave.  I get the following error message when I email to your address.  Not sure where it's coming from - my ISP or yours or some place in between.  I'll keep trying.
 
   550 5.7.1 *** We do not accept spam ***

Hey! I'm no spammer

Cheers,

Peter

Dave,

It's gone through now.  Wonder why they thought a compressor was spam?   :roll: