Re: [Discuss-gnuradio] Re: synchronizing sound cards in a cluster

[Dave Emery]

On Thu, Mar 13, 2003 at 03:50:02PM -0800, Steve Schear wrote:
> At 01:28 PM 3/13/2003 -0800, you wrote:
> >> I believe Matthew is exactly correct regarding the crux of
> >> the problem and if someone were to discover a sound card with
> >> an external clock would appreciate learning about it.
> >
> >Check out http://www.rme-audio.de  they have cards which do this.  They 
> >also
> >have a 128 channel card, and they have been supportive of ALSA.
> 
> Does the upcoming USB 2.0 card have a master/slave clock locker?  Might be 
> nice for multiple card systems.
> 
> steve

        As I have said in another post, I think that there are two
related features that would be most useful.

        1.  External trigger input (and ideally also output allowing
multiple cards to be slaved to each other without needed an external
source of sample clock)).

        2.  Some provision for using an external standard frequency
reference to generate sample timing, thus allowing highly accurate
GPS time and frequency to be used for precise sampling where 
one cares about exact sample frequency.   Accepting a 10 mhz industry
standard reference frequency here would be ideal.


        But by far the most important requirement is 1a - the ability
to accept an external sample trigger input (TTL or LVT).   Any gnuradio
oriented design that omits this feature is fatally flawed in my 
opinion.    The other capablities are simply window dressing designed
to make it easier to generate a master sample timing signal in typical
applications - but the ability to synchronize sampling across multiple
boards is of rather significant importance for quite a host of 
applications (especially interferometry) and not readily done without.

        And certainly for the kind of things I am playing with at the
moment it would be of some importance to be able to lock sampling
to a known edge related to the GPS time base thus allowing remote
sites to sample in sync...



-- 
        Dave Emery N1PRE,  address@hidden  DIE Consulting, Weston, Mass. 
PGP fingerprint = 2047/4D7B08D1 DE 6E E1 CC 1F 1D 96 E2  5D 27 BD B0 24 88 C3 18