I'm a newbeginner when it comes to signal processing. I'm reading up about anti-aliasing, Nyquist and band-pass filters. There's something I don't get: Anti-aliasing in analog filters.
Lemme try to explain. I use a 8th order analog butterworth band-pass filter (centered at 17.5 Hz with a 25 Hz 3dB bandwidth) on the analog signal. So it cuts at 5 and 30 Hertz and ofcourse there's the transition-band before the stop-band. It is supposed to be an anti-aliasing filter. Where is this anti-aliasing happening?
I asked my teacher before he left why the butterworth was called anti-aliasing filter when it didn't really do it. He answered that since I was working on the analog signal, it was just a band-pass with no anti-aliasing because this was before ADC. The aliasing only occur after the ADC when the analog signal is made to digital and digital filters are used. WUT?
I mean, the anti-aliasing still happens when the signal goes through ADC, right? (well, I sample at 512Hz so I oversample the signal but stil...) So why is the filter called anti-aliasing filter?
Could someone explain this to me? I totally don't get it. Why is it called anti-aliasing filter and where does this anti-aliasing happen?