Analog Output Noise

[ronnie]

I've got the HP XW4600 pretty much squared away with the SCOPE Pro, Pulsar 2 and Luna 2 cards in it. Yesterday I pulled the analog output from the Pro (XLR) and I noticed a lot of noise coming through the monitors. It goes away only when the machine is off. I tried the Luna II outputs and that seems somewhat better but not much. I don't remember having so much noise with my old Dell 8250 but that was quite awhile ago. It definitely sounds like RFI and I don't know where it's coming from but it's seems to be inside the case. At one point I was able to hear what sounded like a Citizen's Band transmission but otherwise it just sounds like RFI. The Pro cables have the toroid around them and the Luna II has the jacks more "internal" on the card itself if that has anything to do with the slightly quieter Luna II outputs.. The noise becomes apparent when the Mackie Big Knob volume is around 9 o'clock. When I take the output from the MOTU 828 Mk II and A/B the analog outs with the SCOPE outputs, the MOTU can go to 11 o'clock before the noise equals the SCOPE output. Since I only use any analog outputs for monitoring it's not a problem for recording and even at 9 o'clock the volume is sufficiently loud. I can get more headroom out of the MOTU if need be which picks up SCOPE through ADAT. I've tried different cables, balanced and unbalanced, played with the trim on the Big Knob to get the optimal noise floor and even put a Hum-X between the computer and the outlet with not much difference. The only thing I haven't tried yet, because I have to run an extension cord, is connecting the computer to the APC line conditioner / voltage regulator which my laptop and MOTU come out of. Any ideas would be appreciated. Again it's more of an aesthetic thing with the monitoring (and not recording) to keep the meters even all around (which they pretty much are) but some more quiet headroom would be nice. Thanks in advance.

[garyb]

it's either a poor ground in the building, poor grounding schemes between gear(for instance the computer and the speakers on different circuits), poorly grounded/bad quality cables or a ground/power supply issue inside the computer.

or all of the above...



of course, there is bound to be SOME noise. if you have to turn the volume way up to hear it(with no music playing), then it's probably not a real issue.

[ronnie]

Thanks gary. I am running the new system off of a different mains. I'm going to hook everything up as it was in the Dell 8250 days through the same filtered mains and see if that helps. Thanks, as usual.

[ronnie]

I wasn't able to lower the noise floor much by moving the XW4600 with SCOPE 5.1 to the same filtered mains as the laptop with MOTU 828 Mk II but it seemed to help a smidgeon. I adjusted the control room output through the Luna 2 up about 3 or 4 db and also put the SoftEnhancer on it and was able to squeeze out almost 4db more without appreciable noise or coloration through the monitor mix. Clearly the RFI is from the XW4600 and not the Luna 2 per se because I put the Gate S on the Luna outs with no difference. Since this is only for monitoring it's fine.

[garyb]

is the laptop on battery or ac?

use transformer-type line isolation between the two systems.

[ronnie]

The laptop is on AC and the noise is really much less than the XW4600. I will try a separate line conditioner for the XW4600 just to cover all bases. I'm going to try the Tripp Lite LS606M 600 watt Line Conditioner 6 Outlet 120 volt which I just picked up on Amazon for $69.40. I might be cheaping out on this as it only has 20db suppression. If that's not enough I'll probably spring for the APC G5BLK 9-Outlet G-Type 15-Amp Rack-Mountable Power Conditioner which has 55db but is twice the price. Thanks for the advice. I have had better noise isolation in the past with other laptops running on battery but this one is unusually quiet either way.

[garyb]

sorry, for a minute, i thought that the issue was when the laptop and desktop were connected together.

a line conditioner probably won't make any difference, but if you have it, you can try it. i think something like this would be a better bet, but again, i'm just guessing based on your description:
http://hosatech.com/product/hem-462/
or at least
http://www.behringer.com/EN/Products/HD400.aspx

if this has nothing to do with connecting the laptop to the desktop computer and you're just connecting one system or the other and noting the differences in what you hear on the monitors, the above isolation transformers(hum eliminators, should help when connected between the desktop(or the Luna) and the speakers. if the building doesn't have a good ground, you might need those things between every bit of connected gear that is not balanced. in that case, the ground on the building would need to be fixed(it's always good to have a good ground). i'd say that since audio from the laptop is clear, that it's just an issue with the desktop and speakers and not the building, in which case, the hum eliminators are likely to succeed and work instantly.

of course, not every audio device has the same noise floor. what is normal for one audio device might be a disaster for another, in terms of noise...

[ronnie]

NP. I've been using Hum-X devices for forever with good results for ground loops. The problem here is not 60Hz hum or buzzing but higher frequency noise that sounds like EFI or RFI.

[garyb]

yes, that can be caused by grounding issues too. did you try the humx between the computer and the speakers?

how many db down is the noise? i would expect some processor noise in the built-in audio and maybe even in the Luna card, there's a lot of stuff going on inside the case, and case grounds can be an issue, too. but if it's well below -80db and you have to put on headphones and turn up the volume, then it's no big deal.

[ronnie]

I played with the gain trim on the Mackie Big Knob some more and put a toroid on the input side to the Mackie from the Luna out. I got it down around 7db or so more. I can live happily with this and if the Tripp-Lite doesn't have much to add it wouldn't hurt to give it to my son for his setup.

[ronnie]

The final frontier! The Tripp Lite LS606M 600 watt Line Conditioner 6 Outlet 120 volt did the trick. I've got about 40db total clean monitoring headroom squeezed out.

[dante]

Good one ! Will add this to the Trouble Guide...

[ronnie]

Still trying for perfection here!!!!!! All the above is all good however.... I noticed something: If I move around the STM 2448 in the routing pane the noise changes. Granted I have to be pretty full up on the monitors to hear it but when I slide around the mixer the noise fluctuates around, down and then back when I stop. I deleted the STM 2448 from the routing pane and the noise is gone! Of course I need the STM 2448 so this is not a solution. I disconnected all the ins and outs and even deleted the devices while experimenting but it's only when the STM 2448 is gone that there's no noise at all. Is this strange? I'm going to try other mixers just to make myself crazy. I don't hear it on printed material (although I should record a hot blank track just to make sure) just hear it out of the live studio monitors from Scope. Any thoughts on this? Maybe it's the STM 2448. I also stripped it clean with no effects and no ins and outs and it's there. A gate does nada... it's in the STM 2448 circuits or else it's so good it actually gets RFI!

[astroman]

that's quite normal and not related to any (virtual) audio circuits
it's the load on the graphics engine - you can get it with any moving device or menu pulling
level indicators also hand a nice piece of extra load over to the CPU

check your CPU meter, then minimize Scope's routing window, bring it back up again...
that should give you a good idea about what's going on

normally it's only on monitors, it doesn't bleed into tracks while recording
(but any ground loop will gradually increase the volume - which is not RF-noise)

cheers, Tom

[ronnie]

It's really weird because when I move it around the noise gets lower! I've got a GeForce 610 with 2GB on Win 7 so I don't really think it's an issue. The only time the noise goes away is when the STM 2448 is out of the pane or Scope 5.1 is closed. Again it's no big deal but I'm crazy obsessing over it. I guess it's time to let it go!

[astroman]

if the system detects the state 'moving' it may consequently reduce redraw interupts
another cause for 'reduced noise' might be a shift into unhearable frequency ranges...
at least your description reads fairly familiar...

cheers, Tom

[ronnie]