Audacity Forum

This is a bit off the topic of Audacity, but maybe someone experienced in using small digital audio recorders can help me. I tried recording an interview in the home of a subject this evening and immediately noticed a low, electronic hum. We turned off the computer in the same room. We turned off a fluorescent light. We turned off the guitar amplifier in the son's bedroom and the t.v. in another room. We even turned off the refrigerator. We tried moving to different parts of the house. Still got a low, steady hum, even after unplugging and reseating the 1/8" external microphone connector.

I'm using the Olympus WS-320M with the matched Olympus external lapel mic. Any suggestions about what I could have tried next?

Michal

Did you have the recorder plugged into the wall, or was it running on battery power only? Also, has this ever happened anywhere else?

If it were plugged into the wall, you might have picked up ground loop hum or mains hum. If you can use Audacity to analyze the file, highlight a portion with only hum (no talking in the background) and click Analyze -> plot spectrum. Change the upper right menu to at least "1024" (the higher the better, but if you don't have enough audio selected, you can't use the bigger numbers, find a bigger piece of 'silence'), and change the lower right menu to "Log Frequency." Do you see a big spike at 60 Hz in the spectrum that's now displayed? If you do, that's mains hum:
http://en.wikipedia.org/wiki/Mains_hum

It's tough to get rid of without using the dangerous method of using a plug adapter with no ground pin (don't do this even though it will work, you have been warned). Try using a different plug in the house. You might even have to go so far as to run an extension cable from somewhere else to remove it. The only safe way to get rid of the hum from a plug is by re-wiring it with better ground cables (or the "star ground" method that would drive the electricians insane very quickly).

If you're getting hum when using batteries, then this is a tougher problem. It's probably bad equipment in that case, most likely a bad plug or cable.

The Olympus digital recorder is battery operated. I'm using an external microphone with 1/8" plugs, one for the microphone itself and one for the cord. The hum has happened only once before, in a stadium where recording was just fine the day before. Since the recent recording session, I haven't been able to reproduce the hum.

I'll run the Analysis procedure you outlined, but the interview itself is trashed . . . good only for notes toward rescheduling another interview.

Thanks for your help!

Michal

<<<immediately noticed a low, electronic hum.>>>

Immediately? Or when you went to capture the performance in the computer? Plug good quality headphones into the recorder on batteries (alone) and listen in a quiet room. Is it still noisy?

There is a temptation to power USB electronics and interface systems from the USB bus itself. It saves on batteries. The other thing it does is mess with the audio quality because noise from the computer gets into the show.

Try capturing through a USB hub that plugs into the wall.

Koz

Thank you all for helping me think through the problem with the recording hum. I'm working with minimal gear by choice to produce audio-driven slide shows. For audio I use the battery-operated Olympus WS-320M digital recorder which cannot be plugged into wall current. The external microphone I use is the tiny Olympus noise-canceling accessory ME52W which can be jacked directly into the recorder itself or connected by an extension cord and lappeled to a subject. And I think THAT was the source of the hum I've experienced using this combination. Setting up to work outdoors yesterday I got the same persistent hum again. Unplugging and rejacking the extensiion cord into the recorder didn't resolve the problem, but then I unplugged and reseated the microphone itself at the other end of the cord, and the hum vanished.

I've read that these 1/8-inch connectors are notorious for not fully engaging, but it didn't occur to me to check both ends of the connecting cord during the previous equipment check. Simple stuff. It's always the simple stuff.

Thanks again for your suggestions.

Michal

And the engineering reason for that is in the design of the socket. A three conductor mini-plug contacts the tip and ring with opposing spring contacts inside the female connector. The shield has no spring contact, it's only connection is through the friction of the person pushing in the plug--and further, the other two contacts work against a firm ground contact.

Alcohol and a couple of paper towels work wonders with contact problems like this. Rub the male connection once wet and then once again dry. One of those little sample bottles of vodka is highly recommended. It's small and contains distilled water and pure alcohol. Stay away from flavored varieties.

Koz

Stay away from flavored varieties.

What? No Scotch?

Boooooo.

<<<What? No Scotch?>>>

Too may evil contaminants. But I can think of other desirable applications.

Koz

There is nothing evil about Scotch. Take that back.

<<<There is nothing evil about Scotch.>>>

Only if you happened to be a polished nickel electrical connection, but you're right, I haven't actually tried it. Can I borrow some of yours?

Koz