In a message dated 12/21/2006 10:44:29 Pacific Standard Time, [EMAIL PROTECTED] writes:
1 second raw samples: 10.40 ns then removing small linear frequency offset, 1 second samples: 9.36 ns 30 second averages: 9.62 ns 300 second averages: 10.0 ns Did I do something wrong? PHK, what do you think about this? /tvb Hi Tom et. al, Has anyone tried looking at this sawtooth/bridge noise in the frequency domain, then using brick-wall FIR or better IIR low-pass filters below the modulation frequency of the bridges, and sawtooth? There are IIR low-pass filters that can be extremely efficient (>>120dB stopband attenuation) with only a small number of coefficients. Matlab is great to calculate these based on passband/stopband response etc. With a bit of memory, it is would be possible to do a 512-tap IIR or FIR low-pass filter for example with a 1/100Hz to 1/1000Hz cut-off frequency. The sampling frequency is 1Hz of course. For fun this filter could be scaled to 96KHz sampling frequency, and would then be equivalent to a 96Hz to 960Hz brick-wall low pass. Essentially simple averaging is a really "poor-mans" FIR low pass filter with all coefficients set to 1.0. We should be able to do so much better than that with IIR filtering, especially since the frequency behavior of the sawtooth, bridges, etc seems to be somewhat well understood and the filter can thus be highly optimized to filter out exactly these periodic noises. Has anyone tried something like this? bye, Said _______________________________________________ time-nuts mailing list [email protected] https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
