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Re: Filter poles...

At 05:24 PM 4/26/2003, Jesse Ray Lucas wrote:
>Sorry to go OT here, but I have been looking around online and can't 
>out what the difference between a 4-pole filter and a 6-pole filter is.
>Does it have to do with the amount of gain that can be applied/cut by the

"pole" refers to an aspect of the mathematical description of a filter. I 
guess the best way to understand it intuitively is to think of a frequency 
response plot of a filter, which you have probably seen. They have 
frequency along the x-axis and the gain on the y-axis. A pole will be an 
inflection point along the frequency axis where the slope of the curve 
changes negatively by 6dB/octave. For example a single pole at 5 kHz will 
cause the gain to start sloping downwards, such that it will be 6dB lower 
by 10 kHz. Several poles together means the slope changes that many times 
more. So a 4-pole filter will have the gain slope change by 24dB/octave, 
and a 6-pole filter will have the gain slope change by 36dB/octave. In 
other words, the 6-pole filter is a more drastic gain cut than a 4-pole 

The opposite of a pole is a zero, which is a point in frequency where the 
slope changes more positive by 6dB/octave.

there's a lot more that goes into a filter design than that, but hopefully 
this answers your question.


Kim Flint                     | Looper's Delight
kflint@loopers-delight.com    | http://www.loopers-delight.com