everyone. Recently, I am doing simulations about filtering a linearly chirp signal, and have been confused about the result. The signal was linearly chirped from 0 to 1000 Hz. At first, the chirping rate is set to be 50 Hz/s. When the signal was filtered in time domain by a band-pass filter (Butterworth 500-600 Hz), the result was
--The first line of plot shows the signal
--the second line is the fft of the signal
--the third line is just the zoom in of the second line of plot.
We can see that the filtered signal corresponds to the pass band of the filter. 10 s corresponds to 500 Hz, and 12 corresponds to 600 Hz.
since 500 ~ 600 Hz correspond to the time scale in 0.051 ~ 0.061 s (500/9850 ~ 600/9850). We can see the filter signal has been delayed and extended. Addition to that, we can see that the envelope of the filtered signal is oscillatory.
Is this normal or caused by improper parameter setup? Will I get the same result if the filter is an analog filter?
Any advice is greatly appreciated and thank you for your help.