removing "hum" from an audio recording

select part of the wavefile where there is only the hum. Click Effects/Noise Reduction/Noise Reduction click "Get Profile from Selection" and adjust the slider in the preview mode to the desired value. click close and select the whole wave, then call that filter again and click OK.

If the hum is at 120 Hz, you need to filter everthing below about 200 Hz to get enough attenuation.

Best is usually to use a notch filter at 60 or 120 Hz (or both). However, some hum signals contain harmonics that exists at much higher frequencies, these cannot be readily filtered.

Luhan

How did you record it? Can you listen to the tape deck with phones plugged into the tape deck. How are you playing it back. What AC connections are made during recording and playback?

greg

Hello Micheal,

You really need what is called a "notch filter". In fact you'd need several because most hum isn't just 60 Hz but also 120Hz, 180Hz and maybe higher. This is due to dimmers, cheap motors, switch mode supplies and all that.

I am not familiar with audio software or what filter features they have. However, you might want the ask the pros in this newsgroup: alt.audio.pro.live-sound

Stay cool. Heard it's going to be 107F this coming weekend. Whew...

How did we record it? Co-worker also brought along two microphones (one UHF wireless, another wired), along with his video camera. Then we discovered that for legal reasons we couldn't videotape the conference.

However, we found an ancient Sony tape recorder (with analog signal meter!) and power supply in a box. Plugged this right up. We did some tests - everything sounded ok. Then I had this great (horrible?) idea

- let's move the equipment closer to the laptop, which was driving our Powerpoint presentation. Then we unexpectedly started right up - no chance to test. (No headset to monitor the input, unfortunately.) Then, after the presentation, re-wound, and... hum!

Possibly from the power strip, or the projector, or the laptop... or maybe from the wired microphone.

md

No kidding... sounds like South Lake Tahoe is the place to be...

Thanks,

Michael

Hello Michael,

Oh boy. Could be direct coupling from the laptop power brick. Those can be nasty. I guess you really need software with freely programmable multiple notch filters. Google search the ham radio community, for FFT and sound card software. They often have similar problems to tackle, usually trying to fend off on-the-air noises that can be similar.

Thanks! That noise reduction trick removed my synthetic 60Hz sine wave tone.

Will try this on the tape when my co-worker comes back in to work - unknown to me, he took Tues-Thurs off too. (And, he has the tape.)

Michael

Try and download a copy of Cooledit 2000, its gat a notch fliter system that is rather excellent. Low pass is not the right tool for this sort of thing.

For example my Canon XL1s produces shit sound, nice bit 150Hz hum, I just knock the fundamental down by 30dB, no problems

martin

Hello Joerg,

What's the big deal about a balmy 107? It hit that in Tucson yesterday and summer doesn't start until tomorrow morning [g]. It cooled off today... only 102.9 at 3:50 PM.

A comb filter might work, phase locked to the hum fundamental.

They're predicting 116°F in Phoenix on Friday. Time for you Easterners to drop by ;-)

...Jim Thompson

Thats why I moved here from Quartzsite: normal mid-summer temps there peak at 130. No records are set, because there is no official temperature taken there.

Luhan "The Desert Rat"

Does anyone live in a house there? All you can see from I10 is trailers ;-)

...Jim Thompson

martin griffith wrote: Try and download a copy of Cooledit 2000, its gat a notch fliter

Good choice but hard to get. After Adobe bought Syntrilium, they renamed CoolEdit Pro Audition and removed CoolEdit 2000. I have looked around for it but I haven't found it. Audition sells $349. Its a shame they got rid of the $69 2000. It was really good.

GG

The houses there are all north of I-10; about 1 square mile. I was in a 32 foot motorhome with no ac (the compressor was already in 'thermal cutout' from the ambiant temperature). I had a makeshift swamp cooler that put out 110 degree's if you sat right in front of it.

Even most of the locals leave town for the summer. A few years before I was there, they had a 'hot one' - hitting 136 reqularly.

Now the worst I have to deal with, is the walk to the mailbox on a hot day.

Luhan

The three frequencies you mentioned will kill almost all of it; a low pass with 3dB point near (say) 5KHz will take care of the spikes which are individually not too energetic, but add up to most of the balance of the noise. This all ASS-u-MEs that the fundamental is 60Hz; modify the three if

just found this

I dont know if it works, since I already have cooledit

martin

With drop being the key word!