Re: [Audacity-devel] Build Audacity on XP ?

[AndyB <An...@xe...>]

Richard,
See below.

Richard Ash wrote:
> 
> AndyB said:
> 
>>Compressor.  Briefly, the RMS function calculates an RMS envelope that
>>is averaged over a short period.  The Follow function uses this RMS
>>envelope with a set of compression rules to come up with the compression
>>values for the samples. These rules include factors which govern the
>>maximum rates that the compression value can change by, sample-by-sample.
> 
> I wonder if that architecture is ultimately part of the problem, or at
> least making it harder. As I understand it in a hardware compressor, there
> is only one attack control, which alters both how fast the audio level is
> determined and how fast the gain is varied, because the two steps are
> performed with the same circuit. 

Actually, no. I have an ancient "Compressor/Gate" unit from dbx, model
226 - obtained from a store that specializes in instruments and equipment
for such as rock bands. It was the low end of such professional
equipment. It is analog in and out.  It works extremely well.

It's primary objective is that the low end of the rock concert has to be
louder than the crowd, while the high end of the concert cannot break
ears (actually, they do, but it takes a while), consequently,
compression is required.

I have it permanently connected to my home stereo and activated whenever
  I am using the stereo for background music, which is most of the time.
It is actually a dual unit, each 'side' can be worked independently, or in
a joint stereo mode.

Getting now to the point:  Compressor part of each side has
  o Threshold    o Slope   o Attack time   o Release time  and  o Gain

I generally set it for:  Thresh -40 dB;  Slope 2.5:1;  Fast-moderate
attack; moderately slow release, and 20 dB gain.  (This difference in
attack and release times is, subjectively, very important.)

I found that, for my listening of classical music, I preferred that the
amount of compression was best placed over the entire dynamic range of
interest.  However, I noticed that, for rock concerts, dbx's app notes
suggested  stiffer settings:  higher slope over a shorter range (hockey
stick).

<snip>
> The other issue is that in most real systems a box called a compressor
> will be multi-stage, with a noise gate, a compressor and a limitter in one
> box, using the same gain control element and three seperate amplitude
> folowers. This means a lot of variables to adjust, but fine control over
> the sound.

Well, my dbx is a "real system".  However, high end professional units,
as you have indicated above, are much more complex.  Quite some time
ago, I called the Engineer at a local classical music station (WBJC,
Baltimore) who gave me a rundown on the topic.  They were using a unit
that had 5 or 6 breakpoints, whose settings could be saved/retrieved as
a profile.  These profiles could be programmed to activate for various
parts of the day.

During commuter hours, they would use a high degree of compression,
anticipating that many of their listeners would be driving (ha!, my
application).  Midday they would use a moderate degree, and the least
amount of compression was used for the evening.

He gave me the impression that it is common practice for radio stations
to use at least a moderate degree of compression.

Andy