Questions regarding P.S. noise

rootbeer · 05-13-2008, 08:12 AM

Hello, I am a new forum and Reaper user.
I am new to digital recording but fairly proficient with electronics and computers.
When recording with my laptop I was getting a very high noise level. The noise did not sound like 60hz hum or a multiple thereof. It was a very broad spectrum noise.
Here is my equipment situation:
Dell Latitude D610 P1.2ghz, 1Gb ram, 60 Gb H.D., Reaper of course
Behringer 8 channel powered mixer/p.a. - pre-amp output into internal sound card line-in. (I know this is bad and I would welcome comments on recommended improvements).
After trying all sorts of different input combinations (different channels, cables, guitars, etc.) I finally decided to unplug the power supply and run on the battery. The noise completely vanished! Is this normal? Should i expect this kind of noise from a laptop power supply?

ngarjuna · 05-13-2008, 08:22 AM

I'm far more ignorant of electrical/interference noise than I should be, but I had a similar situation at my place:

I am running my monitors unbalanced (that's about to change, yay!). Whenever I would power on my 2nd screen, I would get an annoying buzz.

On a whim, I decided to try a different outlet (I suspect it is on a different circuit, but I haven't gotten around to verifying that yet) and sure enough, the buzz no longer appears.

This reminded me of the old days when I would very carefully look for isolated circuits to plug my PA into (to avoid the inevitable hums that came from sharing a circuit between audio and lighting). I have read some about ground buzzing, but not enough to have much of a handle on the background concepts.

Diogenes · 05-13-2008, 08:26 AM

Quote:

Originally Posted by rootbeer

Hello, I am a new forum and Reaper user.
I am new to digital recording but fairly proficient with electronics and computers.
When recording with my laptop I was getting a very high noise level. The noise did not sound like 60hz hum or a multiple thereof. It was a very broad spectrum noise.
Here is my equipment situation:
Dell Latitude D610 P1.2ghz, 1Gb ram, 60 Gb H.D., Reaper of course
Behringer 8 channel powered mixer/p.a. - pre-amp output into internal sound card line-in. (I know this is bad and I would welcome comments on recommended improvements).
After trying all sorts of different input combinations (different channels, cables, guitars, etc.) I finally decided to unplug the power supply and run on the battery. The noise completely vanished! Is this normal? Should i expect this kind of noise from a laptop power supply?

This is an "infamous" problem with some Dell laptops. Lemme Google a bit and I'll be back with a solution...

Your power supply uses a three prong plug right? That allows a ground loop to occur and the noise filters in to the PC. Buy a three to two adapter so the ground lug is not connected to the mains supply. The laptop is still safe as the PSU is double-insulated. I knew I had heard this one before. The guy reported that this quieted his laptop nicely.

D

ssj4vegita2002 · 05-13-2008, 10:03 AM

As for a solution to using the line-in on the internal sound card, I'm loving my Edirol FA-101 firewire interface. the thing rocks. And if you don't need the 10 inputs, you can grab it's little brother, the FA-66. Bother are surprisingly low cost compared to how they perform. I can reliably get 4ms live monitoring latency.

This is all on an HP DV9000t laptop, 2.5ghz core2 duo, 4gb ram, 2 120gb 7200rpm drives.

The Muffin Man · 05-16-2008, 03:25 AM

Quote:

Originally Posted by Diogenes

This is an "infamous" problem with some Dell laptops. Lemme Google a bit and I'll be back with a solution...

Your power supply uses a three prong plug right? That allows a ground loop to occur and the noise filters in to the PC. Buy a three to two adapter so the ground lug is not connected to the mains supply. The laptop is still safe as the PSU is double-insulated. I knew I had heard this one before. The guy reported that this quieted his laptop nicely.

D

Man, don't do it. The ground prong is not there for nothing, in case of malfunction it allows the ground to suck the current and burn the fuse. The laptop is insulated as long as you dont touch any metal parts, however plug in a guitar or mic...

maa · 05-16-2008, 05:00 AM

Quote:

Originally Posted by rootbeer

I finally decided to unplug the power supply and run on the battery. The noise completely vanished! Is this normal? Should i expect this kind of noise from a laptop power supply?

Yes - my D400 does the same.
Definitely not earthing noise so forget the ground loop tips.
I'll be trying a Kensington P.S. tonight to see if that gets rid.

For the others:
The sound is like you can hear all the bits going through the processor - windows opening / closing / mouse noises - you name it and whats worse it is not limited to the on board sound card either. My Phase X24 picks it up too.

Cheers

maa

Lucian · 05-16-2008, 11:08 AM

I have had this problem with my dell laptop as well and found that it is due to the built in mic being left on, I can't remember exactly which setting fixed it but there are only three places. double clicking the speaker icon near the clock in bottom right window, the sigmatel or whichever sound card is onboard, usually acessible from the control panel, and right click/my computer/manage/device manager. Setting the mic to off in the wrong place seems to be ignored but once the true off switch is found for the integrated mic, you should hear blissful silence and not the harddrive hehe. Good luck

maa · 05-16-2008, 11:31 AM

Quote:

Originally Posted by Lucian

it is due to the built in mic being left on,

Hmm - that doesn't explain why pulling the P.S. kills the noise....

maa · 05-16-2008, 12:50 PM

Anyhow - here's the noise made by the Dell P.S.:

PS_Noise.mp3

The Kensington 120W PS is dead quiet!

rootbeer · 05-20-2008, 07:49 PM

Thanks all for the suggestions...
An update:
During the next recording session, I used an adapter to lift the ground on my laptop power supply. This did eliminate most of the noise. By trial and error i found that when I used the line out/sends of the guitar/bass amps directly into the computer the noise was reduced. It was worst when using mics into the behringer mixer then into the computer. Must have been a ground loop between the computer and mixer. I'm not sure whether to blame Dell or Behringer for this.

maa...I still do have the "computer" type noises you described. I can't get rid of them completely but i found that disabling all wifi/network adapters reduces the frequency of them. Right now my reaper level meters idle at about -70db so I'm pretty happy with that for an amateur!

Off topic but f.y.i. I purchased the m-audio fast track pro usb interface to get away from using the internal sound card. I'm happy with the performance now but it was a pain to install as the drivers will NOT install if you have XP SP3. You must uninstall SP3, then install the drivers, then reinstall SP3. Takes a long time so be forewarned.

rootbeer · 05-20-2008, 07:53 PM

Also, I forgot to point out.
Running on batteries still provided the least noise of all so I still unplug the power supply during the actual recording.

Zed Maestro · 08-22-2008, 10:19 AM

Need some help here.
I want to eliminate the noise coming out of my keyboard amplifier when my laptop is plugged into an electric socket.

The noise disappears when I unplug the power supply and run on battery. Also, there is no line noise when my headphones are plugged in, even when the power supply is connected.

My Equipt:
I run Native Instruments B4II software on my new HP laptop with Windows Vista. I have an external SoundBlaster 24 bit card that connects via USB to my laptop. I run a line from my Headphone Out jack to my Roland keyboard amp. (There is no line out on the sound card. But there is a SPDIF out.)

I play live with a band using this equipment. The laptop battery can only last a short time, and I don't want to take the chance of running out of 'juice' during a gig. But, the amount of noise from plugging-in AC to the computer is too loud to be useful.

Please Help.

bigtop · 08-22-2008, 12:30 PM

I had this problem...got a new PSU which was 2 pin and the noise went away.

I dont think you need a three pin PSU...most laptops have a 2 pin PSU and the connector that plugs into the laptop is only 2 pin..yes?

http://forum.cockos.com/showthread.php?t=24212

See above thread.

martygras · 08-22-2008, 12:50 PM

This is one instance where using a ground lift may be ok to do, but there is another alternative too.
Ebtech and Behringer make a 2 channel hum eliminator.
The Behringer is $20 and the Ebtech is $60ish.

I always carry one in my magic box o' goodies. They eliminate most problems I've encountered running sound including several other peoples laptop problems.