[LAU] open hw soundcard (was Re: status usb2 for sound)

[Folderol]

On Sun,  8 Nov 2009 16:53:31 +0100 (CET)
karl at aspodata.se (Karl Hammar) wrote:

> Folderol:
> ...
> > I started looking at the USB2 protocols for something else, but gave up
> > when I saw how insanely complex it is even for relatively simple data
> > transfer. In the end, for my project, it was easier to convert the data
> > into an RS232 serial stream then use one of the standard serial-USB
> > converters.
> 
> Well, then you could design around a ft232 [1].
> But would RS232 suffice for 8ch/24bit/44.1kHz (12Mbit/s) ?

My project was relatively slow speed. RS232 wouldn't begin to come close
enough for even 1 channel :(
The FTDI chip would just about manage one channel, but I don't know how
you'd convince the host computer that such high baud fake serial is
possible.

> Shall I interpret your answer as the main hurdle is not to convert
> x channels at real time, but to get it into the computer?

Indeed. the conversion itself just requires a very stable clock signal
and an accurate ADC for every input and DAC for every output - well
that's the theory :).

Getting that lot into the computer - now that's the art! I'm not aware
of any open designs, even for a pretty basic sound card, which must
tell its own story.

> Would a network connection solve that problem?
> In that case the DACs and ADCs could reside on an embedded computer
> and stream the sound data to/from the pc. And one could envision
> such little things near each mic and ethernet cables or possible wifi
> to the control room. Power-Over-Ethernet [2] could be helpful, and why
> not throw in a pre-amp and plug it directly into the mic.
> 
> Regards,
> /Karl
> 
> [1] http://www.ftdichip.com/Products/FT232R.htm
> [2] http://en.wikipedia.org/wiki/Power_over_ethernet

Ethernet looks interesting, and I know there is stuff out there, but
have no idea what latency and timing issues there may be. I would
imagine syncing multiple 'drops' to a stable clock might be problematic.

If you're just multicasting an audio stream neither of these is
especially important.

P.S.
I could be quite wrong about most of this - it has been known to
happen :)

-- 
Will J Godfrey
http://www.musically.me.uk
Say you have a poem and I have a tune.
Exchange them and we can both have a poem, a tune, and a song.