Re: [LAD] [ot] rme fireface: weird balanced output measurements

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To: <linux-audio-dev@...>
Date: Monday, February 20, 2012 - 4:01 am

On Sunday, February 19, 2012 10:17:31 PM Fons Adriaensen did opine:

> On Sat, Feb 18, 2012 at 08:28:03AM -0500, gene heskett wrote:

Actually, driving a 600 ohm load on the bench, the heat rise of the chip
doing the output I was monitoring, was only barely detectable. Failures,
when there were failures, were usually in tensies or so, in the wake of a
passing thunderstorm that nailed the STL tower.

> > So now the problem is levels, digital doesn't come

Not in normal automation programming, its pretty much a hard digital
switch. If we start fooling with it, lip sync problems rear up and byte us
on the butt. The board with actual gain controls is only used during live
newscasts, and in pre-production making of the files used in those
newscasts (used to be tapes), there the gain is controlled usually by the
reporter as he does the editing to get 5 minutes worth of the file from the
camera's hard drive, down into a minute thirty or so package that tells the
story as compactly as possible without leaving out any gory details unless
they really are gory and next of kin hasn't been notified yet.

Really overpowering to the point of digital clipping or even phase
reversals, generally get flagged by the on duty switcher, and John will
yell at the src the next day to make them redo the production with a normal
audio level. We do probably 55% of the production in this market, the
other guys do about 25-30%, leaving the national agencies doing the
remaining stuff, and they are the worst offenders by far.

It seems to me, that a scan of the file done ahead of time, or if its
really fresh, the first time it airs, and using that average data to
develop an average volume level, then run the audio thru a D/A which then
feeds a multiplying A/D running at the same clock speed, with the
multiplier being that whole program average loudness, should be able to do
that fast enough that lip sync isn't a problem. Once determined, that
digital gain value should somehow be tied to that file in such a way that
it is applied before the first frame of video on subsequent playbacks.

The IT & production managers are actively looking for something that would
help, but so far, their searches have only managed to come up with stuff
similar to the old analog frame synchronizers, at 5 digit and up prices.
The system integration to make it work is, as I see it, a bigger problem
than the hardware, which it seems to me could be thrown together for under
a 200 bill a channel, and all four of the channels we would need could
possibly be in one box. Or we could go 8 channels & be playing one file
that needs massaged thru a 'preview' circuit to derive the gain that
spot/program needs the next time it plays for real.

Hardware, to me, seems relatively simple, but of course the devil that will
raid the fridge and eat your lunch, is in the details.

Even a digital gain control developing the A/D multiplier voltage would
seem to me, to be something we ought to be able to buy for maybe
$150/channel/box. That would give the operators a real time, darned near
pure digital gain control.

If somebody were to take a stab at this, I suspect, given enough noise made
in our comm channels & industry rags, you might need a ladder to reach the
side of the hog, for a while at least. We aren't a walmart sized market of
course.

The commission is about to take action if they haven't already, and this
may force the issue, opening up a limited market, but one that could keep
10-15 people on a production line, busy for a few months.

Cheers, Gene
--
"There are four boxes to be used in defense of liberty:
soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
My web page:
"From there to here, from here to there, funny things are everywhere."
-- Dr. Seuss
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Messages in current thread:
[LAD] [ot] rme fireface: weird balanced output measurements, Jörn Nettingsmeier, (Fri Feb 17, 12:32 pm)
Re: [LAD] [ot] rme fireface: weird balanced output measureme..., gene heskett, (Mon Feb 20, 4:01 am)
Re: [LAD] [ot] rme fireface: weird balanced output measureme..., Jörn Nettingsmeier, (Sat Feb 18, 12:45 pm)