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help with filter design-urgent

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aruna1

Member
hello guys I have to design a band pass filter for high quality audio crosoveer circuit.
following are the given condidtions

filter range : 3kHz - 20khz
stop band attenuation : 80dB/decade
distortion in pass band should be minimum

can someone tell me how to decide maximum pass band attenuation to get high quality audio output
thanks

P.S. friend told me that if we take maximum pass band attenuation as 3db filter qulity will decrease
 
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mvs sarma

Well-Known Member
hello guys I have to design a band pass filter for high quality audio crosoveer circuit.
following are the given condidtions

filter range : 3kHz - 20khz
stop band attenuation : 80dB/decade
distortion in pass band should be minimum

can someone tell me how to decide maximum pass band attenuation to get high quality audio output
thanks

P.S. friend told me that if we take maximum pass band attenuation as 3db filter qulity will decrease
if you are interested in passive filters, you may see a free filter design /analyser software at AADE Filter Design and Analysis

Hope this helps
 

MikeMl

Well-Known Member
Most Helpful Member
Passive LC filter or do you want an active opamp filter?
 

MikeMl

Well-Known Member
Most Helpful Member
sorry my mistake.it is a active filter

Go to the TI website and download their free FilterPro application. It'll get you started.
 

aruna1

Member
well i know about this software.but my problem is not designing it but how to choose maximum pass band attenuation.
 

audioguru

Well-Known Member
Most Helpful Member
You do not want pass band attenuation.
Instead you want frequencies below 3kHz and above 20kHz to be attenuated at 80db/decade which is 24db/octave which are forth-order Butterworth filters.
 

aruna1

Member
You do not want pass band attenuation.
Instead you want frequencies below 3kHz and above 20kHz to be attenuated at 80db/decade which is 24db/octave which are forth-order Butterworth filters.

we need some pass band attenuation value(Amax) to calculate order of the filter right?

-80 ≤ -20log[1/√(1+ε²(ωsp)Λ(2N)]

ωs-stop band edge
ωp-stop band edge
N-filter order
ε= √(10Λ(Amax/10) - 1)


with 3db i get order of 4
 

crutschow

Well-Known Member
Most Helpful Member
we need some pass band attenuation value(Amax) to calculate order of the filter right?
Why do you call Amax the pass band attenuation. That would appear to be the pass band gain. Attenuation is what occurs in the stop bands.
 

aruna1

Member
well i'm talking according to slides set based on microelectronic circuits by sedra/smith

here is the slide set.
i used notation used there
 

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audioguru

Well-Known Member
Most Helpful Member
The slope of a Butterworth filter is simply 6dB per octave per order. You want 24dB/octave so the order must be 4 which is a pretty steep slope.

A Butterworth filter with any order is -3dB at the cutoff frequency.
 
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