HI A little more information:
If you are doing the ADC thing, you still need to estimate zero crossings. In all likelihood you would be doing bandpass filtering first (say 8 Hz to 12 Hz) on your 10 Hz note. Next you would do some sort of estimator to get the zero cross. A curve fit is one sort of estimator, there are others. A simple straight line fit over 4 or so points might do it. A higher order fit over a few more points is possible. Why does that matter? The fit improves your accuracy quite a bit. It also reduces your vulnerability to odd single sample issues like popcorn noise. Since you are running at a very low frequency 1/f noise can be an issue. Bob On Oct 12, 2014, at 2:37 PM, Hal Murray <[email protected]> wrote: > > [email protected] said: >> Does it matter that the ADC in the sound-card is probably clocked by a >> crystal clock that is 50ppm off and has bad ADEV? > > You can calibrate the clock on the ADC. > > One way is to feed a known reference frequency in on the other channel. > (That's assuming you have a stereo setup and don't need the second channel > for something else.) > > Another way is to compare the sample rate with the PC clock. That will > correct for any long term drift but may not track shorter transients. > > -- > These are my opinions. I hate spam. > > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
