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Old 16th January 2006, 05:10 PM   #1
APaddy is offline APaddy  United Kingdom
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Default 3rd order HIgh pass filter - explanation?

hi guys

can anyone give a detailed description of what a 3rd order high pass filter is???

what is the 3rd order part ???

and also how to calculate the cut of frequency???

thanks guys
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Old 16th January 2006, 05:33 PM   #2
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A high-pass filter lets the highs pass and attenuates the lows.

The filter order represents the number of poles in the system. Basically the higher the order the steeper the cut-off slope.

I don't have the formulas to hand, but you should be able to find them in books such as Don Lancaster's Active Filter Cookbook (assuming an active filter).
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Old 16th January 2006, 05:48 PM   #3
APaddy is offline APaddy  United Kingdom
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thanks richie00boy for clearing up the 3rd order explanation!!



does anyone know a good website for this stuff...?


need this info for my project report!!!

thanks
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Old 22nd January 2006, 10:09 AM   #4
AndrewT is offline AndrewT  Scotland
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Hi,
I think ESP has a couple of sections on active filter cutoffs and poles(slope), maybe also passive?
http://sound.westhost.com

For passive try Nelson Pass at http://www.passdiy.com
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Old 23rd January 2006, 02:43 PM   #5
APaddy is offline APaddy  United Kingdom
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thanks andrew

will check em out!!!
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Old 23rd January 2006, 02:45 PM   #6
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Download 'Filterlab' from the Microchip website. A wonderful little program for filters up to 7th order.
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Old 23rd January 2006, 02:53 PM   #7
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Quote:
The filter order represents the number of poles in the system. Basically the higher the order the steeper the cut-off slope.
Another way of expressing this is: The order is the same as the amount of components that show a frequency-dependant behaviour (i.e. inductors and/or capacitors) in a filter.

Regards

Charles
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Old 23rd January 2006, 04:07 PM   #8
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Default Re: 3rd order HIgh pass filter - explanation?

Quote:
Originally posted by APaddy

what is the 3rd order part ???
The other people have already answered most of your questions. However, the 3rd order part means that below the cutoff frequency, the level will roll off at 18dB per octave. A first order filter rolls off at 6dB/octave, a second order at 12dB/octave and so on. An octave is a halving (or doubling) in frequency.
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Old 23rd January 2006, 05:34 PM   #9
APaddy is offline APaddy  United Kingdom
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thanks guys

does anyone have on hand the calculations used to caclulate the cut off and 3 rd order part.

thanks
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Old 23rd January 2006, 08:12 PM   #10
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Are you looking for a passive filter calculator?

If so, here's one: http://www.mhsoft.nl/spk_calc.asp
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