[sdiy] 8th order?

[James Dunn]

Magnus Danielson wrote:
>>> 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.
>>>       
>
> Let's take another example. The Oberheim Xpander filter is a 4th order filter,
> but you may use it as a 4-pole Low Pass (-24 dB/Oct),
> or a 3-pole Low Pass (-18 dB/Oct) and a 1-pole High Pass (+6 dB/Oct),
> or a 2-pole Low Pass (-12 dB/Oct) and a 2-pole High Pass (+12 dB/Oct),
> or a 3-pole Low Pass ( -18 dB/Oct) and a 1-pole All Pass (0 dB/Oct). 
>
> Please notice how the multiples of 6 in the low and high pass parts is never
> higher than 4, but may be lower!!!
>   
Interesting, I see what you're saying here.
> They are all 4th order systems, having 4 poles but how these are placed and
> where the zeros are places makes all the difference in the world. The dB/Oct
> number is certainly not telling all the truth either.
>
>   
>>> Thanks again
>>>       
>
> Please keep asking! I enjoy answering these questions. :)
>
>   
Ok - maybe this is stupid question, but I'm not sure what is meant by 
"the zeroes"!
What zeroes?

thanks again,

James