[LAD] FOSS Ethernet Soundcard
torbenh at gmx.de
Thu Nov 26 09:56:07 UTC 2009
On Thu, Nov 26, 2009 at 08:55:50AM +0000, Folderol wrote:
> On Thu, 26 Nov 2009 06:36:07 +0100
> torbenh <torbenh at gmx.de> wrote:
> > On Tue, Nov 24, 2009 at 08:34:53PM +0100, Karl Hammar wrote:
> > > Florian Faber:
> > > > Karl Hammar wrote:
> > > > > [..ethernet transports..]
> > > > > And we are missing an open protocol for this.
> > > > What is wrong with netjack? It's made for point-to-point and very
> > > > simple. You just have to solve the clock issue unless you want to lose
> > > > bit transparency.
> > >
> > > Ohh, sorry, I got the impression it was not ready. I don't mind being
> > > wrong in that.
> > may i kindly ask what gave you that impression ?
> > i admit that some jack versions in svn were broken for the LAN use-case
> > because i am focussing on making it work for wireless and
> > transcontinental internet connections.
> I'm not sure why, but I had an impression of 'unreadiness' too :o
did you try it, and it didnt work ?
> > but the lan use-case it pretty trivial and doesnt need all this deadline
> > machinery.
> > if you just want to build a network soundcard, and use jack on a
> > computer with that, its ready for 3 years now !!!
> The remaining issue then is how much additional latency does netjack
> introduce? I think, eventually, this will turn out to be the most
> critical issue.
if you dont saturate the link, its one period.
you have the same problem with usb soundcards.
for 100Mbit the threshold where you need 2 periods, is somewhere around 12 channels.
> > having more than one network soundcard, and keeping stuff in sync is
> > more tricky. it requires that you can control the wordclock on that
> > soundcard, and you need a special version of alsa_out.c
> > which instead of resampling controls the wordclock frequency.
> If there is no internal sound card, why is there any need for alsa?
> Wordlock may not be as difficult as it first seems. A bit I originally
> wrote to LAU...
if you have a master clock, and want to adjust your output to this, then
the alsa_out program would be what you want.
it extracts the clock driving jackd, and is able to control a resampling
rate so that the phase is pretty constant.
> > Looking up the AES spec quickly reveals 48kHz +/- 10ppm. If the
> > card's master oscillator has that kind of stability, it would surely
> > require only very tiny slow adjustments to keep two of them in sync.
> > Worst case would be them consistently drifting the maximum allowance in
> > opposite directions, which if my maths is up to scratch results in
> > about a second before they would actually get out of step by 1 cycle.
> > A quick google reveals 5ppm temp compensated oscillators with a a 7ppm
> > voltage controlled pull-in - no idea how much these cost though.
> Even without this, I wonder what the audible effect on real music would
> be of just dropping one sample per second. It might be worth doing some
> experiments to find out.
i dont understand why you want that...
> It also occurs to me that although we want to lock frequency, phase
> relationship between cards is a red herring. Signals from different
> sources will not have any phase relationship, so why should the cards?
alsa_out is able to deliver that.
> Will J Godfrey
> Say you have a poem and I have a tune.
> Exchange them and we can both have a poem, a tune, and a song.
> Linux-audio-dev mailing list
> Linux-audio-dev at lists.linuxaudio.org
http://galan.sourceforge.net -- The graphical Audio language
More information about the Linux-audio-dev