[sdiy] Filter terminology question

[Mididood at aol.com]

Hi Gang,

Interesting and highly informative discussion on filter hubbub...

One thing I though may be of assistance - and please excuse if this was 
mentioned as I didn't go back too far in the thread...

I did some time ago (understatement..) get a BSEE - and of course had the 
'filter theory'  classes, etc...bla,bla,bla..

I could never get my mind around this term: 'pole'.

I then, quite recently came across a fantastic explanation of how this term 
came to be used in the first place and it all cleared up for me...I hope this 
isn't too naive or basic on my part...

The term 'pole' comes from the concept of a 'Tent Pole' and how -assuming 
you've seen a big circus tent or whatever - have a pole sticking up in the middle 
and you get that 'response' curve which we usually look at in the 2D plane 
for f'ilter response curves',  but in the 'cloth' of the tent, is actually a 3D 
thing - actually the 'pole' represents a characteristic of the filter response 
(the Q or center freq. of that particular 'pole'), in a 3D plane such as that 
seen when you stick a 'pole' up under a tent and getting the 'draping-off' 
pattern around the whole 360 degrees of the pole - usually a log type of slope - 
so a 3 pole filter, per se, has 3 tent poles sticking up at the freq centers 
(Qs) predetermined by its design, and a 'drop off' depending on their degree 
of cutoff-slope -or 'order'  -   much of this has already been eloquently said 
so I'm not even gonna try and reiterate here - my minds pretty fuzzy these 
days!  I hope I got it right - please excuse if I've confused it any worse....

But I hope that helps in a visualization of the concept of a filter "Pole"

Happy Camping....

Rog
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