Is it possible to use this shield as a band-stop filter?

Is it possible to use this shield as a band-stop filter?

Postby RoyZ » Sun Aug 03, 2014 8:57 pm

Hi friends..

First time here and I'll really appreciate your help! I got an assignment.

I need to create an electronic device that will filter a range of 1 full octave,
half an octave below a desired frequency and half above it.
I want to be inputting a full frequency range of sound and outputting the same sound with the removal of that octave.

This is a one time setting and it will not change often (but it will every now and then) so I don't need any setting components on the device itself.
I want to be able to pick any frequency (20Hz to 20KHz) by putting it in the code I'll have and then uploading it to the Arduino (I Have an Uno) the removed range should be properly filtered, I wish to get the best result in terms of db reduction and with minimal slopes before and after the removed region.

Image

would I better use a "dual" band-pass configuration?

Image

or a low pass filter and high pass filter?

I am not a sound professional but I know a thing or two and I've read some..
I also read that an analog notched filter could remove a frequency better compared to an analog band stop filter in terms of db (generally speaking), but it I understood correctly, notched means it's for a specific frequency and not for a range of frequencies?
I guess going digital will be much better than analog in my case and I could get the best results in the digital way using some kind of filter/s, am I right?

I want to know if it is possible to do what I need with this shield as I didn't see any examples for filters on the examples page..
and if it possible, is it easy to obtain? if it's not, is there any other component here or in general I could use?
one last thing, if it is possible and I'll use a very good sound quality, will it reduce the quality? I can give you some specs of the source audio if it's relevant..

sorry I ask to many newbie questions, I hope you could straighten some things out for me here..

I'll really appreciate any help..

Roy.
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Re: Is it possible to use this shield as a band-stop filter?

Postby guest » Mon Aug 04, 2014 1:22 am

hello roy,

the codecshield does a good job of replicating sound. the main question is if there is enough processing time on the UNO. i do not have any filter examples. i have only made a few, and they were just single pole filters. but im sure someone out there has made a good filter. so if you want to make your filter digital, see if you can find example code. the codecshield should work with any code, as long as it doesnt have too many multiplies (they take longer than most functions).

the decision over notch filter versus HP/LP combination is usually based on the bandwidth you want. the more narrow the bandwidth, the better a notch filter will be. the wider the bandwidth, the better a HP/LP combo will be. a single octave could be done by a notch filter, but the depth wont be so good. you could do a series of notch filters at staggered frequencies to get better cutoff characteristics. or you could go to HP/LP, but i think that might be more processing time.
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Re: Is it possible to use this shield as a band-stop filter?

Postby RoyZ » Thu Aug 07, 2014 10:05 pm

Hi admin..

Thanks a lot for that info, you did educate me but I'm just figuring out I am probably still not educated enough to accomplish this task.. so now I think this project is a little "big on me"..
I wouldn't even know where to look for examples and moreover, how to adapt and try them..

I just got an idea to go on the android route and I may do better there,
but I've read that most of the android devices don't have a low sample rate..

Thanks again for your answer.. I am leaving everything open for the moment.

Roy.
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Re: Is it possible to use this shield as a band-stop filter?

Postby guest » Fri Aug 08, 2014 5:16 am

best of luck with the project. how low of a sampling rate did you want? you could always just throw away samples.
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Re: Is it possible to use this shield as a band-stop filter?

Postby PaulStoffregen » Sat Sep 06, 2014 7:22 pm

Discarding samples without first filtering usually causes aliasing, which polutes the resulting spectrum.
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