> Being that the PC is running software and that software has a delay from
the
> time a signal is present till the time that the software can detect it and
> respond to it, you will have a delay.  Is that delay consistant enough for
you
> would be my question.
>
What sort of frequencies are you talking about ?  I don't know what input
voltages are used on an audio line-in, but you could use a voltage divider
and your sound card.  As long as your signal doesn't exceed 20 kHz, it
shouldn't pose a problem.  This way, you also wouldn't have the problems
w/the delay in Windows because blocks of  information are buffered by the
hardware.  You could then easily parse the generated *.wav file to find
freq/duty-cycle.

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