Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!swrinde!zaphod.mps.ohio-state.edu!brutus.cs.uiuc.edu!psuvax1!psuvm!psuecl!peg From: peg@psuecl.bitnet (PAUL E. GANTER) Newsgroups: sci.electronics Subject: Re: Salvaging recording Message-ID: <91616@psuecl.bitnet> Date: 5 Mar 90 03:20:42 GMT References: Organization: Engineering Computer Lab, Pennsylvania State University Lines: 34 In article , kz08+@andrew.cmu.edu (Ken Zuroski) writes: > To make a long story short, it seems that the condensor microphone in > the unit wasn't properly grounded or whatever, and that there is a > very persistant and annoying sixty-cycle AC hum masking the voices on > the tape. Uh oh. > > Now, the frustrating thing is that it is almost possible to decipher > the voices behind the buzz. Almost. If you turn the volume up, > naturally the noise increases as well, and so it's a futile attempt. > And so I had the idea of using a graphic equalizer to filter out some > of the noise. Here is what I am going to try to do, and what I would > like you to comment on as to the possibility of success. I will use > two tape recorders, the graphic equalizer (when I find one) in line > between them. I will use headphones to mask out as much of the buzz as > is possible using the graphic equalizer, and duplicate the equalized > signal on recorder number two; I'll boost the overall level of signal > in the process, thus hopefully amplifying the voices. Then, if I still Ken-- I think you are on the right track, but instead of using a graphic equalizer, see if you can get a notch filter. CMU has plenty of EE's--see if you can find a laboratory filter that you can use, or have an EE throw together a filter with a couple of op amps. The notch filter will have much better attenuation than a graphic EQ would, and you could tune it to 60 Hz (an equalizer may not have a slider near that--a parametric equalizer is another possibility--they allow you to tune the center frequency of the slider). The cost of a simple op amp notch filter should be < $10. If you need schematics for one, let me know, but any op amp circuit cookbook should have one. Good luck!! Paul