thanks farss

I'll try some of those but 1st I think I may get HP to send me a new adapter. sonic foundry tech suggested that.

the device is a M-audio mobile pre usb. There is no way to power it self.

I have no knowledge of the ferrite chokes. but will learn more if needed.

I know it's not the M-audio because I get the same thing with the onboard sound card through the line input

i've seen similar things with my dell laptop. i haven't found a work-around.
sorry, not much help, but a confirmation of similarity.
b.

It really sounds like M-Audio have slipped abit here. The whole advantage of outboard audio gizmos is to get away from the noisy power supplies in the typical PC. Seems like the noise from the power supply is coming down the USB power line and into the adaptor. It really should have a LOT of filtering to stop this happening or at least an option to power it by other means.

One trick you could try is a powered USB hub running off a quiet power supply.

Also does the noise deminish once the laptop battery is charged?
You see when you first power the laptop up the power supply is powering everything and charging the battery. I'd try waiting half an hour or until it tells you the battery is charged and then see if the noise is any better.

Well, just for the record,
I have a Toshiba laptop with a PCMCIA VXpocket (Digigram) sound card and I never notice any increase in the noise floor with the power unit on. In fact I almost always use it pluged on while recording....
Hope the change of power suply solves the problem, but I remember reading somewhere in the past that some laptops present an isolation problem (earthing? not sure) that could add such a noise.
Good luck,
JTelles

Unless the new power supply is a different design, the chances that replacing it will help are very slim. This is just a sad fact of life these days - poor regulations/enforcement by the FCC of devices that generate EMI/RFI. Many (but not all) of the newer switch mode power supplies generate tons of interference! Outside of the amateur(ham) radio operators, most people are not aware of just how bad these problems are.

I've seen this problem quite a bit when doing spectral measurements in vehicles and studios. The noise is due to grounding issues and noise being generated by the AC outlet. When measuring spectral response curves and tuning a vehicle/room we usually see the noise floor raise 10-20dB when plugging the laptop into the outlet. We end up doing 75% of the work with the laptop plugged in, and when we're near the end of the tuning we unplug it to get a better reading without the added noise floor.

At the homebase I have a heavy isolation transformer on the AC line
going into my equipment. It is not "portable" as it weighs about 20 lbs.

Thanks you guys. 1st I don't think M-audio is at falt at all. It's just another bug to work out. 98% won't even be heard. but in the future I want this to sound better than DATs. The problems not nearly as bad in SF 6.0 it only jumps about 10 db hovering around -55. I can live with that.
It's when I use Vegas for 4 track stuff that it jumps up in th -40s.

My other solution ia a universal battery pack. It's $200 and will give me about 5 hours of recording ( +/- )

datman,
I think the difference between SF and Vegas will just be the metering, not the actual noise being recorded. The noise is getting into the preamps and once it's encoded which ever app youuse to record with should b irrelevant.
Also you will likely find the amount of noise relates to how hard the power supply is working. Potentialy it'll get worse during record than when your monitoring as then the power supply has to drive more current into the CPU and HD. The reverse could also be true.

I've just ordered the Firewire 410, it'll be interesting to see if I have any similar problems with that.

farss,

got the adapter today, did't fix it. I recorded in to vegas noise a -41 saved it and played it in SF, still -41. That tells me it's not metering

Bill

well I figured it out.

it's a ground loop. I used a old radio shack ground loop isolator. the noise is gone

Bill

Glad you figured it out, remember I mentioned this a few posts back?

"The noise is due to grounding issues and noise being generated by the AC outlet."

Rednroll,

yea you did but it's much lower than a typical groung loop. I also discovered I can remove about 80-90% by using a cheater plug lifting the ground and a outlet from my dedicated a/c outlet was almost 10db better than the other outlets

Bill

Hi datman:

glad you found a solution to "your" problem.

Many of the responses here have the same symtoms but may require a different solution to solve:

I am an EMI/EMC Engineer by trade for the last 15+ years. (long enough to know that though I'm considered a guru by many, much of my "magic" is simply troubleshooting and some educated trial and error, til I find "a solution".
Then explain "the problem", once I find what works).

I have the exact same problem with my laptop. I had decided to build an external filter. However, It might just well be a simple gound loop problem
and all i need is to "break the loop" using a cheater plug.

But just to shed a little light for the others with the same problem:

1) The FCC requirements for "line conducted emissions" begin at 450kHz.
(Europe begins regulation at 150kHz). so equip can be noisy as hell below
these frequencies. so there goes a source for hum and buzz in your
audio.

2) Ferrites, clamp-on or otherwise, won't help much in the audio frequency
ranges. If you use ferrites composed of low-frequency absorbtive
material such as 77, 78, or 79, with multiple turns you "might" see/hear
a pinch of improvement. But I doubt it. Most ferrites are designed to
absorb RF energy at >1MHz. And, most readily available ferrites are
useless for audio and low frequency applications.

3) The switching noise level is directly proportional to current. So the other
guy is right that the noise should improve after the internal battery is
charged because the swicher is now drawing much less current.
(NOTE: in this case, it is definitly a problem in the design of the power
supply, or even the components used in the supply. Only a different
design altogether is likely to totally fix this case. ( Or to build something
external to put in line, like I have to do.

4) I have run some simulations on a LC pi filter I designed to get rid of power
supply switching noise. By design, the add-on circuit should work great
and not be too big. I'm still trying to get time to build and test it though.
If I get to it this month, I'll share my findings with others also.


thanks

Rahman

Rahman,
you're dead right. From my experience ferrites don't do much. I just suggested trying as although they've never helped in my case I didn't know enough to know they wouldn't work elsewhere.
Our problem was a fluro on camera light. When powered from the camera noise was getting into the mic channels. Only fix was a pi filter. You do need fair size L & C to have any effect so we had to fit it into a small box that sits on the shoe bracket.

Electrically would be easy enough to do for the laptop power supply, mechanically might be difficult. Also some switchmode supplies are a bit twitchy with too much L/C on their load.

One thing they could try is getting a same spec linear supply or a better switchmode supply. Need some skills with a soldering iron thats all.

The other thing I'm into is adaptors to run the whole rig off gel batteries using DC-DC converters.