> When using a sound card for frequency comparisons the zero crossing time > stamp resolution is improved if the slew rate of the input signal is > slow enough that several (3 or more) samples are taken in the vicinity > of the zero crossing. One can then make use of WKS (Whittaker, > Kotelnikov, Shannon) interpolation to accurately calculate a high > resolution zero crossing time stamp.
Clever. > The instability of the sound card LO isnt completely cancelled if the > zero crossings of the the 2 signals aren't coincident. That seems right for absolute event timing with a stereo sound card but I think for a frequency measurement the delay, if any, between channels would also cancel out (as long as the delay itself stays relatively fixed). We'll know for sure when someone actually tries it. A sound card timing experiment, vaguely related to this, is here: http://www.leapsecond.com/pages/sound-1pps/ There I used a sound card to generate a 1 PPS and measured its ADEV. Note that this is unrelated to NTP (NTP disciplines the CPU or system bus clock, which is typically not the same oscillator as the sound card clock). Win32 source code: http://www.leapsecond.com/tools/1hz.c /tvb http://www.LeapSecond.com _______________________________________________ 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.
