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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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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