microphone hum
in [DSP]
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From: Phil on 30 Jan 2006 23:10 I'm not knowledgeable in DSP, but maybe someone here can help. I have a cheapo electret microphone that is giving a bad hum, at 15754hz and 60hz Any idea for a problem here or a quick fix. It's a cheapo so hopefully you can point me to something simple like installing a new ground or something easy. -- Phil
From: Tom St Denis on 30 Jan 2006 23:58 Phil wrote: > I'm not knowledgeable in DSP, but maybe someone here can help. > > I have a cheapo electret microphone that is giving a bad hum, at 15754hz > and 60hz 60hz is probably from not having a common ground. That's common for desktop computers hooked up to stereos or tvs and getting lines or that hum. As for 15754hz that's probably aliasing from the sample rate you chose. A simple low pass FIR could filter PCM samples for you and eliminate the hum. You could make it a bandpass around 100hz-4000hz if you're doing voice. Tom
From: Allan Herriman on 31 Jan 2006 00:26 On 30 Jan 2006 20:58:25 -0800, "Tom St Denis" <tomstdenis(a)gmail.com> wrote: > >Phil wrote: >> I'm not knowledgeable in DSP, but maybe someone here can help. >> >> I have a cheapo electret microphone that is giving a bad hum, at 15754hz >> and 60hz > >60hz is probably from not having a common ground. That's common for >desktop computers hooked up to stereos or tvs and getting lines or that >hum. > >As for 15754hz that's probably aliasing from the sample rate you chose. The combination of 60Hz and 1575xHz points to interference from a (probably north american) television set or video signal. 60Hz is the vertical frequency, 15750Hz is the horizontal frequency. Regards, Allan
From: Mike on 31 Jan 2006 07:57 Phil- Sorry this is probably a really basic question, but I'm new to electronics/dsp. Read your post with interest. How did you determine the frequencies of the hum? Spectrum analyzer? Thanks, Mike
From: Jerry Avins on 31 Jan 2006 09:15
Phil wrote: > I'm not knowledgeable in DSP, but maybe someone here can help. > > I have a cheapo electret microphone that is giving a bad hum, at 15754hz > and 60hz > > Any idea for a problem here or a quick fix. It's a cheapo so hopefully > you can point me to something simple like installing a new ground or > something easy. You have an analog problem, and you're tight that it has to do with grounding. There are better groups than this for your question, but you're here. so here goes: The 60 Hz is power-line pickup. That commonly happens either through electrostatic pickup because of inadequate shielding -- the shield must be grounded, of course -- or because of hum currents circulating in a ground loop. In your case, I suspect bad shielding (broken ground wire?) because you are also picking up the horizontal frequency of a monitor. Poke around and see what changes. Jerry -- Engineering is the art of making what you want from things you can get. ??????????????????????????????????????????????????????????????????????? |