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Greg Kawchuk
08-05-1998, 08:04 AM
My question involves determining the resampling frequency of a
signal that has been oversampled initially. My end goal is to determine
the first derivative of this signal with respect to time.

I am collecting data and sending control signals from an A/D board at
1000Hz, the rate at which the control signals need to be generated.
Unfortunately, the tasks on the board can not be split with respect to
event speed and as a result, data is collected at 1000Hz as well.

The problem is that for the data I am collecting, a 1000Hz collection rate
results in an oversampled signal. Giannis Giakas has suggested
that the resampling frequency can be found by determining the frequency
content of the signal, then finding the frequency where x% of the signal
is contained.

When this is done, the first derivative of the resultant signal will
dramatically change when resampled at frequencies corresponding to 99.0,
99.5 and 99.9% of signal content (i.e. 3Hz, 16 Hz and 30 Hz respectively).

Can anyone:
1] recommend another method of determining the resampling
frequency?

and/or

2] provide a rationale for why the resampling frequency should
be taken at a specific percentage of signal content?


Thank you in advance. I will publish a summary of any responses.


__________________________________________________ __________________
Greg Kawchuk D.C., M.Sc.
Clinician, University Health Services
Ph.D. Candidate, McCaig Centre for Joint Injury and Arthritis Research

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