On Wed, 2006-07-05 at 10:48 -0700, Christopher Thielen
wrote:
>> >> Hello,
>> >> I'm very new to the Jack audio system
and have a few simple
>> >> questions about what I think would be
it's perfect application to an
>> >> audio problem I'm having.
>> >> I work for the KDVS radio station in
Sacramento, which does
>> >> terrestrial broadcasts as well as
Internet broadcasts, and we have an
>> >> analog audio line out coming off our main
broadcast board into a 160
>> >> MHz computer, which is connected via a
10Mb/s connection to a much
>> >> faster, brand new Dell PowerEdge server,
which has a much bigger
>> >> connection to the Internet to do our
MP3,Vorbis,and Real streams.
>> >> My problem however, is trying to get the
audio line in from the slow
>> >> computer, through the 10Mb/s network, up
to the much faster PowerEdge
>> >> server's line in. I believe this is what
Jack can do, right?
I'm currently running a similar setup and have been for
several years
for KFAI-FM in Minneapolis and I have a couple of comments I
think might
be helpful....
1. I believe that there is at present no way to get live
audio into any
current Real Encoder for stream encoding other than by
letting it read
the port itself directly from OSS. It's a major nuisance.
The encoder
builtin routines read directly from an OSS interface or from
a wave
file. The wave file reader insists on knowing the size of
the wave file
before starting (which limits that input to 2Gb!). Only the
OSS input
can stream continuously (with longer than 2Gb of input
data). It has no
limit at all.
2. There IS a well documented plugin scheme supported by the
encoder
that allows new input driver's to be dynamically linked. In
theory, this
would allow writing a special input plugin for any realtime
source you
want. Unfortunately, the source files for the SDK were so
badly
maintained that the plugin libraries haven't been buildable
under any
modern release of Linux for several years.
3. In the past 6 months, an updated SDK has been made
available from the
"open" helix community server that seems able to
build plugins again. I
haven't had time to get back to the project, but I think
that an open
source plugin (which is well within the terms of the
licenses) is what
needs to be written to solve a NUMBER of interface problems.
(I for one
would really like to be able to use unix pipes to feed audio
into the
encoder for non-real time encoding from our automated
multi-tier
archiving system, as well as feeding the live encoder from
our jack
stack.) At the moment our real time streams and off-line
archives are
fed from applications running from jack WITH THE EXCEPTION
of the real
encoder which is running from it's own interface. (there
are TWO in the
machines). The inability to encode from anything but a wave
file creates
some real problems for our automated archiving system
(especially since
we have some programs as long as 8 hours long).
4. The easiest solution is to wait till I or someone else
gets around to
writing a jack plugin for the Real Encoder. In the meantime,
I suggest
just using two interfaces. The biggest problem is that most
servers
(e.g.Dell Poweredge series). No longer support ordinary PCI
cards! They
only support PCI-X cards. There are very few audio
interfaces available
in this format. We use M-Audio Delta cards which work very
well and DO
support 3.3v PCI-X use. Dedicating one card to real audio is
an
inexpensive solution.
5. There's no reason why you should be getting audio
interference from
the servers if you use a professional tuner and audio cards
and cable
things properly. We use bogen tuners and the aforementioned
M-Audio
Delta card and have no problems of this type at all with our
Dell 1650s
and 1750s.
6. There are a couple of good reasons why taking the signal
off the air
may be a better choice than taking it off your board. We
ourselves ran
into a show stopper here when we tried to take a direct
signal.
Like many FM stations, our station relies heavily on an
Optimod audio
processor for final gain riding and audio balancing.
Modern Optimod's typically don't generate an easily
accessible audio
output of the processed signal. Ours generates a composite
stereo signal
which is sent directly to the transmitter modulator. This
means that the
only easy way to get an identically processed signal to the
one we
transmit is via an off the air monitor.
Over the years, our programmers and technical staff have
grown to rely
heavily on the Optimod for gain riding. Ahead of our
Optimod, our levels
are typically all over the place and not very pleasant to
listen to.
Before we gave up and switched to using the off air signal,
we actually
had to use a second older analog Optimod that did support
audio output
to condition the program signal in order to duplicate the
work the main
digital Optimod was doing and produce a conditioned analog
signal for
encoding.
7. If you're still planning to split things up separated by
a 10mb
ethernet, by FAR the easiest and most reliable way to do it
is to encode
at the near end stream at the far end. A $400 computer
running Linux
will handle the streams nicely. We ran this way for three
years, but we
were using a T1 between the encoders and the colocation
site. Life got
much simpler and more reliable when we moved the encoders to
the other
end, however....
8. I'd be glad to move any further discussion of this kind
of thing off
the list, since Jack is not centrally involved. I do not
work directly
for KFAI (It's a community radio station with only 6
employees), but I
do run a small consulting firm that does this kind of work
and would be
glad to exchange some information with you (or better yet,
do some work
for you if you need some help).
To summarize:
1) I too would like to see a better interface between Jack
and the Real
Encoder, but the project was stalled for about two years by
the broken
SDK. It may be possible to get some work going on that
again, especially
if someone else with Linux C++ experience has some time to
donate. I'd
be glad to explain what I know about the process. It would
be a useful
"hack" for a lot of other reasons. 2) I suggest
taking off-air signals
if possible. They can actually be higher quality. 3) We
couldn't run
KFAI's site without Jack. It multiplexes our live Darkice
encoder with
some monitoring processes and with our real time spooler
that feeds the
archives. It's been running that way 24-7 for many months
at
http://www.kfai.org and
servers thousands of listeners a day!
Mario Vano
Vano Associates
mvano vano.com
Using Tomcat but need to do more? Need to support web
services, security?
Get stuff done quickly with pre-integrated technology to
make your job easier
Download IBM WebSphere Application Server v.1.0.1 based on
Apache Geronimo
http://sel.as-us.falkag.net/
sel?cmd=lnk&kid=120709&bid=263057&dat=121642
_______________________________________________
Jackit-devel mailing list
Jackit-devellists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/jackit-dev
el
|