On Sun, 14 Oct 2012 17:57:08 -0700, I wrote:
> But the compression chip is the original, 25 year old NE572. I'm
> thinking of throwing out that out and popping in a new SA572. Maybe
> they have improved the gain cells in that thing?
> 
> Has anyone tried it and has it made any difference?

I now have an SA572 on order I mean, electronics shop.
I will report on this when I have it in my hands.

Evidently, this part is highly recommended by ON Semiconductor.

They have some workflows on their website where you pick the
kind of thing you're designing. You start with the general
area, like Consumer Applications. Then you can pick some specfic
device type, like Audio Amplifier - Performance. That one
lands you here:

http://www.onsemi.com/PowerSolutions/appDiagram.do?appId=401

On this block diagram if you click on the Audio Noise Gate
block, you are taken to a list of just a handful of parts
for this: NE570, SA571, SA572 and SA575.

I was quite surprised by this: that some junk used in
the ADA MP-1 (or maybe newer versions thereof) is being
recommended for new applications by a semiconductor company.

But that raises my hopes that this SA572 might be a good
part.