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Topic: OS generating speaker monitor noise - how to fix?

  1. #1

    OS generating speaker monitor noise - how to fix?


    I have a set of Mackie HR 824 High resolution speaker monitors and just plugged them into my system yesterday. The first thing I noticed is a background noise that is syncronized to what is on the screen. For example, if I move the mouse I'll hear a faint digital signal in the background. If I am on a website with an add banner, there is sort of a non-stop digital noise due to the animation on the screen. Is there any way to fix this problem?

    I know the problem is not with my speakers because I have them connected to two different systems and the problem only occurs with one of the computers.

    I use Windows XP and M-Audio delta 1010LT with the latest drivers.


  2. #2
    Senior Member Richard Berg's Avatar
    Join Date
    Jul 2002
    Chapel Hill, NC

    Re: OS generating speaker monitor noise - how to fix?

    Usually this is a problem with poor power regulation on the motherboard. I've also seen it blamed on the PSU and soundcard. I'm not sure if there's a definitive answer.

  3. #3

    Re: OS generating speaker monitor noise - how to fix?

    I use a Delta 1010 and it used to pick up some noise until I moved it to a different PCI slot. Since then I've had no problems.
    Might be worth trying to move yours away from the video card if you've got any spare slots.


  4. #4

    Re: OS generating speaker monitor noise - how to fix?

    I had a similar problem that only showed up when running Gigastudio and seemed louder when I ran Gigapulse. I ended up moving my (video) monitor to a different power source than the pc because I noticed that the sound was louder when the monitor was on. It may also be a grounding issue with the speakers or the pc.
    Westgate Studios
    Sound Libraries for Gigastudio and Kontakt

  5. #5

    Re: OS generating speaker monitor noise - how to fix?

    What you can try is to isolate the ground on that computer. Buy one of those 3-prong to 2-prong AC adapters from a local hardware store, so that it lifts the ground circuit on the power cord:

    I've seen it frequently happen with laptops which has the AC ground wired to the negative lead of the AC-DC power supply, connecting to the chassis of the laptop. All digital circuits are connected to the same ground so that's where the noise is coming from.

    Note that it's UNSAFE to keep it that way long term, so don't leave it in there, but at least it will give you an idea whether this is the problem. If it fixes it, you can then invest in a power conditioning/isolation unit.

  6. #6

    Re: OS generating speaker monitor noise - how to fix?

    I've only had this kind of problem with my laptop.
    Any device in the audio chain that allows a "galvanic isolation" should solve it. In my case, it's a standard DI box with "ground lift" on.

    I would not recommend to detach the grounding of any power cord. Musicians (especially guitarists) have died because of doing so.


  7. #7

    Re: OS generating speaker monitor noise - how to fix?

    Hi Karim,

    Without actually hearing the noise it is impossible to diagnose the problem with any accuracy, but your troubleshooting thus far is a big help.

    It appears that some high frequency noise from the computer or possibly the D/A converter (or maybe even both) is getting to the amplifiers in your loudspeakers.

    The RF hash is getting de-modulated, and the only real cure is to stop the RF from getting in there in the first place.

    Even if it is a ground loop induced problem, lifting the ground will probably make it worse as the ground lead that is lifted will now behave like an antenna - if the noise is being induced into a shield or ground.

    What you really need to do is:
    (a) isolate the source of the noise
    (b) fix the problem, and the fix depends on the source.

    There are two paths for noise like this (and remember, this whole thing is based on your description, so I could be completely wrong!) to enter a system, either as part of the signal (more unlikely) or on a conductor that is acting like an antenna.

    The first test is to disconnect the loudspeakers from the D/A and just let them sit next to the computer. Do they still pick up the noise?

    If not then connect the leads to the speakers only and try the test again. are you getting the noise now?

    If not then connect the leads back to the D/A converter again, but insert isolation transformers in-line (you can get an inexpensive isolation transformer at most music stores, Eb-Tech makes one)

    If you are not getting noise now then remove the isolation transformer and check again, but you should have noise, since this is your normal setup.

    If the isolation transformers solve the problem I'd probably just leave them in. If they don't then we'll need to look at other solutions.

    In high end systems the inputs to any stage are usually designed to bypass radio frequency garbage to ground. I don't know if your loudspeakers are designed this way or not, and one fix MIGHT be to add an RF bypass.

    One last note... it is NEVER a good idea, and it isn't even a good troubleshooting technique to lift a safety ground. They are called safety grounds for a reason, and you can probably guess what that is.

    At the very least you stand a good chance of damaging your equipment, and at the worst you stand a chance of damaging yourself.

    Bill Thompson
    Audio Enterprise

  8. #8

    Re: OS generating speaker monitor noise - how to fix?

    Quote Originally Posted by Lee Blaske
    Leave it to a ham to help track down the RF problems.

    Quote Originally Posted by Lee Blaske
    Another possibility... Are all your computer/audio items plugged into the same power circuit?
    An excellent suggestion in general. The big facilities have dedicated power for all audio devices... in many cases even the DAW computers do not get connected to "technical power"! In the small studio setting it is often enough to make sure that everything is fed from the same phase, and that that phase does not support large motors.

    In this case, however, I suspect electromagnetic (EMI) or radio frequency (RFI) trash is getting in.

    Quote Originally Posted by Lee Blaske
    I'd also try re-seating everything, and treating the edge connector of your audio card with a contact stabilant like Caig Pro Gold.
    That's an excellent point. Bad connections can be a source of RFI or EMI, especially at the clock frequencies that computers run at today.

    Quote Originally Posted by Lee Blaske
    Are you running balanced or unbalanced to your monitors? If balanced, I'd try leaving the shield connected at the sending (audio interface) side, and clipping it at the monitor side. If you're running unbalanced, it might help to make cables using two conductor shielded wire. Connect the shield and the minus side on the sending side, but leave the shield unconnected on the monitor side.
    Hate to disagree, but if the problem is EMI or RFI then telescoping the shields as you describe is going to make it worse, not better. Of course I am still guessing about the source of the problem, but I'd save this as a last resort.

    Quote Originally Posted by Lee Blaske
    BTW, I'm not all that familiar with your audio card, but I think you might have a problem plugging the output of the card directly into the powered monitor speakers you're using.
    That would be quite surprising. I am familiar with the interface, and the output can be set to either +4 dBu or -10 dBV if I remember correctly. If it can't then it is set at -10dBV, and in either case, the Mackies ought to be able to connect directly to either level.

    Quote Originally Posted by Lee Blaske
    Pulling down a virtual fader on your computer screen is not a good way to control volume, because you're reducing bit depth and compromising fidelity.
    Excellent advice! So many people don't consider this.

    Quote Originally Posted by Lee Blaske
    Finally, if you ever have a chance to use optical connections rather than wire, choose the optical connection. You can't have a ground loop through something that does not conduct.
    Ah yes... lightpipe is my friend!!! In my studio the computers are not on the same power phase as all the audio gear, and they have no metallic connection to any of the audio gear. It made a big difference. (In order to get rid of the copper S/P-DIF connections I use a S/P-DIF patchbay!)
    Bill Thompson
    Audio Enterprise

  9. #9

    Re: OS generating speaker monitor noise - how to fix?

    A few months ago, I got a Mac G5 with Logix 7.1.1, a MOTU Traveler, with connections to a pair of Fostex NF1A's. As soon as I launch Logic I run into a similar problem. But I never had this happen with a PC running Cubase SX with a RME card.

    Any thoughts, I'd appreciate it.
    Peter L. Alexander
    Learn it right the first time.

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