VO-BB - 20 YEARS OLD!

Jeffrey Kafer · Posted: Mon Apr 06, 2009 12:27 am Post subject: noise at -66db

So I've got a new (to me) computer. All plugged in and everything's working. but I noticed a high pitched hum at a volume of -66db when I record. Tried unplugging the mic, so it's definitely electrical of some kind, and not environmental. Tried switching USB ports, no difference.

My questions:

1) Is -66db an acceptable noise floor?
2) If not, any suggestions for troubleshooting it?
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Frank F · Posted: Mon Apr 06, 2009 12:55 am Post subject:

Sounds like you need an adapter/ground lifter somewhere in your room. But, the simple answer is yes and now.

Yes the actual noise level is OK, but NO a whine or high pitched hum is indicative of something else being a problem.

Toodles

F2
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todd ellis · Posted: Mon Apr 06, 2009 7:47 am Post subject:

mho - -66db is certainly acceptable for your floor - the whine is a problem, though. sounds like a ground issue to me too.
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Jeffrey Kafer · Posted: Mon Apr 06, 2009 10:02 am Post subject:

You can hear a sample at http://JeffreyKafer.com/test/whine.wav. It sounds like a computer is about 3 feet away, when the computer is actually in a different room. Think this is line noise?
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Lance Blair · M&M Joined: 03 Jun 2007 Posts: 2281 Location: Atlanta

Sounds like a computer to interface power issue. I've had that a few times and running things on battery for a bit cooled things down. My Presonus gear whined like that all the time, but my AudioFire is well behaved.
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georgethetech · Posted: Mon Apr 06, 2009 12:54 pm Post subject:

Like F2 said start inserting ground lift adapters. Try your computer monitor first, that's been the source of noise for more than one client. It's the fluorescent light high voltage power supply that usually is the culprit.
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Jeffrey Kafer · Posted: Mon Apr 06, 2009 1:18 pm Post subject:

Is there a certain kind I should get?
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georgethetech · Posted: Mon Apr 06, 2009 2:32 pm Post subject:

http://rsk.imageg.net/graphics/product_images/pRS1C-2266744w345.jpg

Like that
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Jeffrey Kafer · Posted: Mon Apr 06, 2009 2:35 pm Post subject:

Really? is it safe to get rid of the ground? I always thought there was a reason for them...
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Frank F · Posted: Mon Apr 06, 2009 2:52 pm Post subject:

With an adapter, you are not getting rid of the ground, you are allowing the ground to work with a two prong plug.

You most likely will need a two prong male to a three prong male adapter. Not as shown in the picture posted.

F2
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Jeffrey Kafer · Posted: Mon Apr 06, 2009 10:18 pm Post subject:

looks like my original hypothethis of a burned out tube is false.

I'm getting the whining sound with my snowball, too, and that's a direct USB connection, no power cable, no preamp.

Here's a sample

So I'm officially without a clue. Those adapters still worth a shot?
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richvoice · Posted: Fri Apr 10, 2009 11:16 am Post subject:

Hi Jeff,

Just thought I'd throw my two cents in on the ground adapter. The adapter doesn't get rid of the ground connection, it allows a three-pronged plug to be grounded in a two-prong outlet (at least that's what the adapter pictured in the link above does; if, as Frank mentioned, you actually need a different type of adapter, the purpose would be different).

However, it's important to note that an adapter won't create a ground connection where one is missing. The fact that an outlet accepts three-prong plugs does not guarantee that the outlet is grounded, and the center screw on a two-prong outlet isn't necessarily grounded either (that's where the ground connection comes from when you use an adapter like the one in the image link above); the only way to know for sure is to get an outlet tester (relatively cheap and available at most hardware stores). If you plug it into a three-prong outlet directly, or into an adapter connected to a two-prong outlet, you'll know immediately if the outlet is actually grounded.

In new construction, this is rarely a problem, as most three-prong outlets are, in fact, grounded. But in older houses, homeowners (or sons of homeowners, like me) have been known to install three-prong outlets and/or adapters in order to use devices with three-prong plugs, knowing full well that the outlet isn't grounded. This particular son gave full disclosure to his parents: "this isn't to code, and the device might get fried, and it's a safety hazard, but the likelihood of a problem is low." In the absence of a problem, the cost of the adapter/outlet (a couple of bucks) vs. the cost of rewiring the house ($10k+) pointed toward the adapter/outlet solution; if the house ever burns down, a look at the analysis in hindsight might point in a different direction.

Cheers,
Rich

georgethetech · Posted: Fri Apr 10, 2009 12:52 pm Post subject:

I'm no electrical engineer. All I can say is that in more than one case, using depicted 3 prong adapter has solved the high pitch whine noise endemic to some USB audio interface/computer combinations. Maybe I left out the fact that you DON'T screw the tab to the outlet, as that MAY serve as ground in some homes (depending how your outlet is wired).

If someone can explain to me why that doesn't act as a "ground lifter", I'd appreciate it.
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richvoice · Posted: Fri Apr 10, 2009 3:11 pm Post subject:

Believe me, I'm no electrical engineer either!

Googling "ground lift adapter" provided many hits to adapters like the one linked to above; seeing the term "ground lift switch" on one of those pages and then Googling that phrase led me to this article: http://www.audiomasterclass.com/arc.cfm?a=ground-lift-what-is-it-what-do-you-do-with-it-what-do-you-do-if-you-havent-got-it . Interesting reading.

If you're using the standard adapter and not screwing it into the switchplate (and the tab isn't touching the screw consistently, or the outlet isn't grounded anyway), then you would certainly be removing the device-to-earth connection. As I alluded to in my post above, that's not necessarily wise, but it's not necessarily a big deal, either: you just have to recognize that there's a risk when using equipment that is supposed to be grounded without it actually being grounded, and weigh that against the potential cost of replacing whatever needs to be replaced should lightning strike, or a power spike occur, or whatever else might go wrong where proper grounding would avoid the problem.

Cheers,
Rich

georgethetech · Posted: Fri Apr 10, 2009 4:00 pm Post subject:

That's a good little article. Different application, but educational none the less. They mention that a bass guitar isn't grounded, but ever hear of a "waffle burn"? It's named for the pattern left on your lips when you touch a microphone connected to the PA system and there is a large voltage potential difference between the mic and the bass, with your lips as the conductor.
That's why it is generally a bad idea to lift grounds in some situations.
In a home studio, it is usually a "last resort" method to fix a noise issue. Just lifting the ground to your LCD monitor, however, is pretty harmless, really only putting the monitor itself at any risk.
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If it sounds good, it is good.
George Whittam
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424-226-8528
VOBS.TV Co-host
TheProAudioSuite.com Co-host
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