Hum When Using Audacity

[jdmiller]

When I record directly to my laptop using Audacity I am getting a hum which is directly related to my power cord. If I run off of battery power the hum goes away. Would prefer to not have to do this using battery power.

I have tried plugging my laptop into different outlets, but I still get the same hum.

Thoughts??

Thanks,

Jeff

[kozikowski]

<<<When I record directly to my laptop using Audacity>>>

You're singing or speaking directly into the laptop microphone, right? It's important we know exactly what the show is.

Koz

[whomper]

could it be more general?
i copied a friends cassettes to cds for him
he said some of the cds had hum with the music
not all of them just some of them
no hum on the original tapes - they played fine

the hum is a mystery (mine and original poster) as it seems impossible
how could power line hum affect audacity ??

[kozikowski]

If you are recording the internal microphone on your laptop, it's not -- or the power supply is broken. That's why I asked the question.

If your computer is connected to Other Things, then you need to know that the Power Socket Safety Ground (the round pin in the US) is connected to the shield on home audio cables. If your house is wired wrong (I've had two houses with sockets wired wrong) then hum is inevitable. Any combination of bad or missing grounds, funny house power wiring, or defective electric drills can cause problems.

I have one FM radio that I can't record because connecting the roof antenna causes hum -- and it's just the shield on the antenna wire.

The key in the question is that these AC Power problems (almost) always vanish when you cast off shore power and go on batteries.

Koz

[whomper]

shouldn't hum be consistently there? not just sometimes?

[steve]

When I record directly to my laptop using Audacity I am getting a hum which is directly related to my power cord. If I run off of battery power the hum goes away.

Laptop PC power supplies are very often noisy. It's just one of the places that manufacturing costs have been cut.
Using an external sound card will usually lessen (though may not eliminate completely) the problem.

Also, using a device that has "Ground Lift" (such as a DI box or "ground loop isolator") will often reduce the problem. http://www.google.co.uk/products?q=ground+loop+isolator

Some users upgrade their power supply to a non-switch-mode type (not cheap) to remove the problem. Other users just run from batteries while recording, or switch to a Mac. Mac laptops usually have much quieter (and more expensive) power supplies than PCs.

[kozikowski]

We're all assuming the power system is introducing the hum. You can have a bad audio ground and get hum as well. Floating your computer on batteries makes it less necessary to have a perfect ground or shield.

We had hum and buzz now and again in one of the conference rooms and it only vanished when one of the Hardware people got tired of the dance and ripped out the sound cables and put in fresh. Haven't had troubles since.

They do go bad.

Koz