Amplifier power
 

Robert Orban wrote:

says...
Robert Orban wrote:
says...

Thanks Bob !

Him being the one who will be criticised on other groups for making DAB
and FM ever more distorted;!...

All modern DSP-based Optimods can be operated as exremely pure protection
limiters if that is what the broadcaster prefers, and we offer presets to
make this easy. I just make the artillery; I don't have any say in how
broadcasters choose to set it up!

BTW, did you ever use 'optical' compression ? Vactrols etc.

Only once, for a cue amplifier in a one-off broadcast console I built in
the late '60s for a friend's radio station. I drove the lamp from the output
of the cue power amplifier, which made the compressor very cost-effective.

Optical compressors are very interesting because of their complex, program-
dependent attack and release times. However, IMO they are not adequately
repeatable in a mass-production environment, so I never seriously considered
using them commercially.

One of my competitors did (in a four-band processor) and it caused him and
his customers no end of grief with unit-to-unit consistency problems and
temperature sensitivity.

I had them selected by Silonex and we had no such problems.
http://www1.silonex.com/

Their characteristics are indeed very interesting and seeming inherently suited
to music. My first use of them was in a mixer-amplifier to avoid accidental
serious overload. Tuning the time constants you could move the master fader from
'-5' where the amp was briefly clipping (largely inaudibly) to '+5' and you
could whizz the fader back and forth between the 2 points and the sound was
almost completely unaffected. It was as if you weren't doing anything ! It would
allow ~ 1% THD on tone and then cut-in.

More lately we used a Chinese device. Less consistent so required more selection
into grades and the fitting of grade dependent Rs on the control board. 1/8th
the price though.

Graham

Amplifier power
 

In article ,
Robert Orban scribeth thus
In article ,
says...




Robert Orban wrote:

says...

Thanks Bob !

Him being the one who will be criticised on other groups for making DAB
and FM ever more distorted;!...

All modern DSP-based Optimods can be operated as exremely pure protection
limiters if that is what the broadcaster prefers, and we offer presets to
make this easy. I just make the artillery; I don't have any say in how
broadcasters choose to set it up!

Just how smart are the Optimods these days ? I assume they're DSP based now
(oh you said so) and probably for some time.

They're pretty smart :-). All of the manuals are available for free download
from ftp.orban.com, and these provide detailed descriptions of their
features. Our current top of the line processors are the 8500 for FM, the
9400 for AM, the 6300 for digital media, and the 8585 for surround. (The
8585 manual is coming soon; the otehr manuals are currently available.)


I always though your objective was to reduce to the minimum any unwanted
audible artifacts through multiple band processing and the like..

Yes. One can use a special form of multiband processing (with coupled bands
that only uncouple when necessary to prevent audible spectral gain
intermodulation) for protection limiting.

To process for loudness, one really needs to start with multiband processing
and complement it with various peak limiting tricks like distortion-
cancelled clipping, where the clipping distortion is removed in some
frequency bands. The nice side effect of doing such complex loudness
processing is that when backed off to give a more "purist" sound, the
processor causes far fewer audible artifacts than a simpler processor would.


The biggest influence on what a processor can and cannot do is to
untangle the mess made by a lot of radio stations using bit reduced
material on their playout systems and compounding that with more bit
reduction on their STL's..

Sometimes that materiel is transcoded from MP3 to MP2 and vice versa..

There is a local community station hereabouts that has a simple 2200D
and a linear PCM link with a numerical controlled modulator. A lot of
the time they do use MP3 etc as contributions from the community they
serve with predictable results.

But when they play direct off CD the results whilst not quite as "loud"
as the local commercials .. are superb:))..

As is live music content;!...
--
Tony Sayer

Amplifier power
 

In article ,
says...




Robert Orban wrote:

says...
Robert Orban wrote:
says...

Thanks Bob !

Him being the one who will be criticised on other groups for making DAB
and FM ever more distorted;!...

All modern DSP-based Optimods can be operated as exremely pure
protection
limiters if that is what the broadcaster prefers, and we offer presets
to
make this easy. I just make the artillery; I don't have any say in how
broadcasters choose to set it up!

BTW, did you ever use 'optical' compression ? Vactrols etc.

Only once, for a cue amplifier in a one-off broadcast console I built in
the late '60s for a friend's radio station. I drove the lamp from the
output
of the cue power amplifier, which made the compressor very cost-effective.

Optical compressors are very interesting because of their complex, program-
dependent attack and release times. However, IMO they are not adequately
repeatable in a mass-production environment, so I never seriously
considered
using them commercially.

One of my competitors did (in a four-band processor) and it caused him and
his customers no end of grief with unit-to-unit consistency problems and
temperature sensitivity.

I had them selected by Silonex and we had no such problems.
http://www1.silonex.com/

Their characteristics are indeed very interesting and seeming inherently
suited
to music. My first use of them was in a mixer-amplifier to avoid accidental
serious overload. Tuning the time constants you could move the master fader
from
'-5' where the amp was briefly clipping (largely inaudibly) to '+5' and you
could whizz the fader back and forth between the 2 points and the sound was
almost completely unaffected. It was as if you weren't doing anything ! It
would
allow ~ 1% THD on tone and then cut-in.

More lately we used a Chinese device. Less consistent so required more
selection
into grades and the fitting of grade dependent Rs on the control board. 1/8th
the price though.

I forgot to mention that we at Orban have had substantial experience with
optos, but not for use with compressors. In the mid 80s, we did some R&D for a
digitally controlled analog parameteric EQ that used optos as the
variable resistance elements for adjusting Fc, BW, and gain. We used dual
optos driven by a single lamp, with one side handling the program audio and
the other side having DC applied to it to close a servo feedback loop. This
made the control law predictable and stable. We relied on close matching of
the two sections of the opto, particularly over temperature.

Because the optos had too much soft nonlinearity to produce state of the art
distortion measurements, we eventually dumped them and ended up going with
MDACs even though the latter caused audible glitching when the controls were
operated, unlike the optos, which sounded completely smooth. But the MDACs
were much more linear.