[RDD] Audio Processing -- was -- normalization (Alan Peterson)

Chris Howard - CBR cbr at elfpen.com
Fri Jan 24 08:45:00 EST 2014

Thanks for all of the good information.

My content is almost all home-recorded readings of classic
books.  You can try some out at librivox.org.

So there are level problems and audio problems in a lot of the cuts.
For one-piece cuts I can cull out bad stuff but for larger
works where there were multiple collaborators I can get
a bum cut in the middle of a work  ( e.g.  one chapter in a book).

I'm not aiming for perfect audio, which would be impossible
given my source content.  But I would like to do a
reasonable job at level control.

Some cuts have hum and other artifacts that would be nice
to lose if it could be done without blood, sweat and tears.

Some kind of look-ahead AGC would be really nice, and the
normalization thing may be enough.  I'm not sure I care about
latency and other live-audio type features, not at this
stage of the game.

The trimming tool in the RDLibrary program is letting me
snip off intro and extro stuff.  I wish I could also x-out
an internal piece, but I can live without that.  And I am
trying to do leveling work at that stage but when I
play the cut back it is always at the same level no matter
where I set the  cut gain.  Or it sure seems that way.
So I am just going 'by eye' with the red lines and the
general visual fullness of the spectrum.

This is going to go out over the air on a new LPFM
and we hope to do streaming also.

Besides for just general production work, I am getting sales
information about LPFM transmitters and they all tout
the idea of having audio processing in the transmitter box.
But what I need may or may not be what they have in there
and I'm trying to figure out if there is any "savings!"
for me in buying such a transmitter, as the manufacturers seem
to think.

Side-chain gate is new terminology to me, so I'm going to do some study on that.

I very much appreciate the good responses to my questions.
You are helping me a lot.

Chris Howard
Classic Book Radio

On 1/23/2014 6:47 PM, Jim Stewart wrote:
> I think ideally you need a “simple and slow” AGC-like compressor that has a “side-chain gate” so that it can be adjusted so it doesn’t “pump up” the level during silence periods that are “supposed” to exist in spoken word.
> I don’t know what kind of “Radio” station you are running, but you likely will have some sort of processing needed for guarantee legal operation (as well as generating a proper “composite” signal if an FM) which might be able to be able to be adjusted to do this already.  If you need to buy one, perhaps the lowest priced Omnia or Optimod products (appropriate for your type of station) would work once properly adjusted to do what you want.  Otherwise my vote is an Aphex Compeller, that I think can be “slowed down” enough to give the processing you desire.  It certainly has the side-chain gating you need.  Overall it is an excellent single-band AGC/Leveler product but does not provide “final radio broadcast limiting” needed for legal operation.
> If you like to try to do it in software inside your Rivendell box, and have Jack Audio running, there are lots of processor plugins (like ones previously mentioned in this thread) that can be used.  I’m using a simple single-band compressor for a web-streamed version of our FM station and have it working great for our purposes (my exact choice would not be best for you as it has no gate, but you might be able to find one that does).
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