Sub Nyquist Sampling Rate

[signal1]

I need acceleration data in the 2 - 1000 Hz range. 

However my hardware analogue filters are low pass at 20 kHz. 

Sampling at 40 or 50 kHz is just too high - there's just too much data. 

If I sample at a rate high enough to use the filters - say 20 kHz (do I need 21 or 22 kHz to allow for filter response?(the filters are 5 pole Butterworths)) - will any foldover leak into the low frequencies needed?  In other words, a cutoff at 20 kHz should be fast enough for a 10 kHz signal so I should be clean at 1 kHz and below - right? 

Thanks,

Bob

[rpursley8]

If you data is up to 1 kHz, then your Nyquist limit is 2 kHz.

But if you are worried about other noise signals between 1 kHz and 20 kHz entering into your data, then you should

1.  Find analog filters with a lower cutoff frequency

2.  Sample at 40 kHz to avoid aliasing, filter the data digitally to (lowpass with a cutoff above 1 kHz), then then decimate your data by a factor of, for example, 10 (new sampling rate of 4 kHz) to reduce your data size.

[signal1]

Thanks, Randall.

Your help is appreciated and understood.

I will have some problems sampling that fast (my computer halts with an "out of memory" error) after a few seconds) but I certainly try 40 kHz again. 

Respectfully,

Bob