[time-nuts] Re: Low cost synchronization, kitchen appliances

John Ackermann N8UR jra at febo.com
Sun Aug 21 13:53:14 EDT 2005


Alberto di Bene wrote:

> Hmmm, the sound card used is the M-Audio Delta 44, a professional sound
> card, used also by musicians and composers for studio works. I don't
> know the accuracy of its time base, but certainly it is quite good.

I previously did some rough accuracy tests of my Delta 44 cards and
found they were "pretty good" but I didn't record the results.

Just for the fun of it, I am now measuring one and see about a 1.5Hz
error at 25kHz -- that's 6x10e5.  The setup is an HP3325A synthesizer,
locked to an Rb standard, feeding 0.5v p-p into the Delta 44 on an
Athlon 2200 running the Linux-based Baudline spectrum analyzer program.
 I'm sampling at 96kHz and decimating by 4096; Baudline has a very cool
measurement function that will give the absolute frequency reading with
a resolution of better than a mHz.  I'm measuring ~24998.5Hz against the
nominal 25000Hz.  The Delta 44 has been running in the computer for
several weeks, so it should be thermally stable.  I've attached a
screenshot of the Baudline display.

One thing I want to explore is how difficult it would be to provide an
external clock for the Delta 44.  Higher-end boards in the M-Audio
series have a "wordclock" input, and I suspect that the Delta 44 PC
board may be hackable to enable that.

John
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