Chirp!

[battler]

Hi all,

Lets all head back to basics.

The chirp response of a digital filter, could someone explain to me what it all means?  That is, I've applied a chirp signal to a low-pass Butterworth filter and what I get back is a rising pulse from 0Hz which ends at or around the cut-off.  I've done this also for a Chebyshev, what I'm getting is much the same though it appears to oscillate in the passband.

What I'm required to do is compare the 'chirp-response' of a few specific low-order filters (Butterworth, Chebyshev Type 1, Equiripple).  I have the results, though honestly I have no idea what they're telling me.  Please can someone help.

Thank you all very much.

BTW I've been experiencing some problems with LabVIEW 8 such as slow-running (for instance when I alter the Properties of a graph), it's frozen and even crashed.  Overall it's notibably slower than 7; reminds me a bit of MatLab in this regard.  Bring on the 8.1 I say.

[johnsold]

Chirp is a term to describe a signal that sweeps across a range of frequencies, as you may be aware. If you are trying to obtain the frequency response of the filters this is one method which could be used. Just make sure that the frequency of the stimulus does not change so rapidly that the transient response of the filter masks the measurement you want to make. The Chebyshev filter has ripple in the pass band, so the "oscillations" you are seeing may be what is expected.

Can you post your VI along with the specifications of the measurements you are trying to make. "Chirp-response' does not really specify anything. Do you want to compare plots of magnitude vs. frequency and phase vs. frequency against theoretical curves or something else?

Lynn