[icecast] Gain control

Tim Pozar pozar at lns.com
Sun Jun 24 16:21:17 UTC 2001

On Sun, Jun 24, 2001 at 01:51:05AM -0700, Dave Hayes wrote:
> How are people doing gain control, out of curiosity? 
> I know boxes exist (anyone have names and mfrs?) that ride the gain
> for big radio stations, ensuring that there is no distortion and
> raising the volume of songs recorded at a lower volume. I'd probably
> buy one if I knew what to buy.

This is a bit tricky and subjective.

If you are doing streaming and broadcast, some considerations you
will have are:

        * Brick wall filtering to prevent "all ones" distortion

        * Soft limiting and compression for increased loudness

        * AGC to reduce dynamic range to keep the music above
          ambient noise (ie. office and car locations.)

If you are just doing streaming and don't care about loudness or
limiting dynamic range, you just need a smart clipper/limiter of
some sort.  My favorite is the Aphex Dominator.  I have been using
them for a bit more than 10 years for processing before A/D converters
like Sony F1s and later DAT machines.  The Dominator does a great
job of limiting those occasional nasty peaks (pops, clicks, feedback,
etc.) without sounding like it is punching holes in the audio.
The audio stays pretty "transparent" sounding.

If you are in a loudness war (ie. broadcasting) and/or concerned
about dynamic range you need some sort of AGC-compressor-soft
limiter combination.  Aphex happens to make another favorite unit
for this called the "Compellor".  It isn't as aggressive as other
processors such as Bob Orban's, or Frank Foti's boxes but it is
"transparent" with good AGC and some loudness.

Both the Dominator and Compellor can be found popping up on Ebay
at least once every couple of weeks.  Try to get the "Mark 2"
versions of each unit.  The Compellor model 320 is their second
generation unit.  If you are doing FM broadcasting, you need to
get the dominator that support "pre-emphasis" such as the "722".
I have picked up 320s for about $400 and the Dominators go for
about $600.

Of course Aphex will sell you their "combo" unit the "2020" for
about $5K retail.

If you want something cheaper (and of course not as good sounding)
there are a couple of companies that build "compressor/limiters"
boxes that run in the $150 range.  The Alesis "3630" or the Behringer
"Composer Pro MDX2200" can do the job of hard/soft limiting and
even some AGC/compression so long as you don't push them too much.

If you are interested in a "how to" of setting up your new processing,
drop me a line.


  Snail: Tim Pozar / LNS / 1978 45th Ave / San Francisco CA 94116 / USA
               POTS: +1 415 665 3790  Radio: KC6GNJ / KAE6247
"It's a damn poor mind that can only think of one way to spell a word."
                        - Andrew Jackson
"What is wanted is not the will to believe, but the will to find out,
which is the exact opposite." - Bertrand Russell, "Skeptical_Essays"

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