[sdiy] 8th order?

[James Dunn]

Magnus Danielson wrote:
> From: James Dunn <james at 4thharmonic.com>
> Subject: [sdiy] 8th order?
> Date: Tue, 05 Jun 2007 10:40:03 +0100
> Message-ID: <46652F73.3050707 at 4thharmonic.com>
>
>   
>> What does 8th order mean? Is it simply another way of describing the 
>> number of poles in a filter or db/oct?
>>     
>
> It relates back to the theoretical background of linear diffrential system
> and describes the degree of the system. The order of the system also descibes
> how many poles and how many zeros the system can have. The placement of the
> zeros gives the db/Oct number, but the school-book examples with all zeroes in
> a bunch over at infinity for a low-pass makes the db/Oct being -6.02 db/Oct
> times the order. An n-pole system is of the n:th degree.
>
> You require at least n reactive components (capacitors, inductors) to acheive
> a n:th order system, but it is not always that you get that order, you can get
> less. For example will a dual-PI notch filter with RC links have 3 capacitors
> but only show up as a 2:nd degree system. The db/oct measure does not give a
> good measure here.
>
> I hope you see the difference and also apprechiate why we talk about 8th order
> rather than 48 db/Oct systems.
>
>   
er, I'm afraid not! Thanks very much for your in-depth answer though - I 
think I need to spend some more time with the Arts of Electronics.. :) I 
also think I have a good enough understanding for what I need for the 
time being though.

Thanks again

James
> Cheers,
> Magnus
>
>
>
>