Forums

60Hz Notch filter at 25kHz sampling rate?

Started by abradley1984 August 28, 2008
>"abradley1984" <abradley1984@gmail.com> wrote in >news:AsGdnV6jK46fsiXVnZ2dnUVZ_hWdnZ2d@giganews.com: > >> >> I'm aware of the harmonics of 60Hz, which I'm ignoring for now because >> I'm really only looking at frequencies up to 100Hz at the minute. >> And in case your interested, it's recorded data, interneural >> recordings, and I did my utmost to avoid noise during recording. > > >That's different. The first question is "what are you trying to do.
I'm looking at the neural firing pattern, so I need higher frequency info to see the spikes. However I"m applying stimulation at 10-50Hz, and need to see if there's a response at this range . If
>its identify spikes, you might consider high-pass filtering instead of >trying to notch out your line noise. If you really really need the >waveform, and it has real info in the 50-60 Hz range, you might want to >reconsider. If I were refereeing, I wouldn't like it. Does "utmost" >include Faraday cage? >
Utmost includes a sound proof booth, which I think includes a faraday cage.
>To decimate, you need to low-pass filter first, and you might lose some >valuable signal. > >Another quick and dirty trick would be to FFT, zero out the 60 Hz >component, and then ifft. If it doesn't work, you haven't wasted much >time. >-- >Scott >Reverse name to reply >
So:  My efforts with Matlab filters failed.  I can't get a notch filter
with a small enough bandwidth for my purposes, even with the signal
decimated by 4 to a Fs of 6250.

Maybe someone else could do better.  

I also tried the correlation subtraction method to no avail.  

Finally, I decided to leave the 60Hz in.  I don't think it's interfering
with any useful data, it just makes my graphs look bad.  I don't think it's
worth distorting important information to remove it.  

Thanks again for everyones help.  I've learned a lot in the last few days,
hopefully I can apply it some time in the future.

Allison

>>"abradley1984" <abradley1984@gmail.com> wrote in >>news:AsGdnV6jK46fsiXVnZ2dnUVZ_hWdnZ2d@giganews.com: >> >>> >>> I'm aware of the harmonics of 60Hz, which I'm ignoring for now
because
>>> I'm really only looking at frequencies up to 100Hz at the minute. >>> And in case your interested, it's recorded data, interneural >>> recordings, and I did my utmost to avoid noise during recording. >> >> >>That's different. The first question is "what are you trying to do. > >I'm looking at the neural firing pattern, so I need higher frequency
info
>to see the spikes. However I"m applying stimulation at 10-50Hz, and
need
>to see if there's a response at this range . > If >>its identify spikes, you might consider high-pass filtering instead of >>trying to notch out your line noise. If you really really need the >>waveform, and it has real info in the 50-60 Hz range, you might want to
>>reconsider. If I were refereeing, I wouldn't like it. Does "utmost" >>include Faraday cage? >> > >Utmost includes a sound proof booth, which I think includes a faraday >cage. > >>To decimate, you need to low-pass filter first, and you might lose some
>>valuable signal. >> >>Another quick and dirty trick would be to FFT, zero out the 60 Hz >>component, and then ifft. If it doesn't work, you haven't wasted much >>time. >>-- >>Scott >>Reverse name to reply >> >
"abradley1984" <abradley1984@gmail.com> wrote in
news:s-OdnS-9Z53OuSfVnZ2dnUVZ_uCdnZ2d@giganews.com: 

>>Vladimir Vassilevsky <antispam_bogus@hotmail.com> wrote in > news:OWduk.25815 >>$Ri.11814@flpi146.ffdc.sbc.com: >> >>> Although 25kHz for EEG is definitely an overkill. >> >> >>Is that what Interneural Recordings are?? If so, the frequency range >>of > >>interest goes to about 100Hz, so 500Hz should be all you need. >>-- >>Scott >>Reverse name to reply >> > It's not EEG, I'm obviously no explaining myself very well. I'm > basically sticking a microelectrode into the nerve and recording from > that. So I need higher frequencies to see the spikes.
Do you JUST need to see the spikes, or do you need more information than that? Do you need to distinguish one type of spike from another?? Do you need to recover the resting membrane potential?? Given what you're doing, your sample rate isn't so crazy. Try HIGH PASS FILTERING at about 150 Hz cutoff, and see if the result is acceptable. No need for a tight old notch filter when you don't particularly care about the low frequency stuff. Since the noise seems to be in your soundbooth, any Faraday cage built into the walls isn't helping you. You'd need a cage around your physiology. -- Scott Reverse name to reply