Help me debug RF noise

Discussion in 'Recording/Live Sound' started by jzucker, Jul 26, 2004.

  1. jzucker

    jzucker Supporting Member

    Messages:
    20,296
    Joined:
    May 20, 2003
    Location:
    Home of the ex-world champion Cavs
    Using a notebook computer, a mackie 1202 and an Maudio Firewire 410 interface:

    I'm getting some sort of RF noise. Sounds like I'm picking up a wireless network, cell phone or wireless phone.

    If I unplug the power cable on the notebook, it reduces the noise by 50%. Turns out I'm getting 2 different types of noise. One steady one and then an intermittant one which seems like it's RF noise. I'll try the ground lift on the notebook computer and I assume that'll fixe the steady noise since the noise partially abates when I unplug the notebook but the other noise seems to be generated by the cables going from the line outs of the maudio and into the input of my mackie 1202. If I disconnect the maudio, the mackie is dead quiet. On the other hand, if I disconnect the mackie and run the maudio direct to my monitors (and with the laptop unplugged) it's also dead quiet. Sounds like the cables are introducing the noise. I've tried several different cables but it does the same thing. The mackie has balanced 1/4" jacks going in but unfortunately the maudio has unbalanced line outs.

    Any other thoughts?
     
  2. MichaelK

    MichaelK Member

    Messages:
    6,479
    Joined:
    Jan 7, 2002
    Location:
    Fort Mudge
    Are the line outs from the 410 balanced? If so, are you using balanced cables and using balanced inputs on the Mackie? Most Mackies have balanced line inputs somewhere, though I don't know about every channel. If not, this could be the problem. If the 410 does not have balanced outs I don't know what to suggest, other than maybe moving to a different room.

    I'm not sure what you mean by using a "ground lift" on your laptop (mine has no such animal), but if your laptop has the option between a 3-prong or 2-prong plug (like a Mac) I'd suggest using the 3-prong.

    I'm always reminded of Spinal Tap on the Air Force base when that happens. It's a major pain in the ass, I know. Good luck.
     
  3. jzucker

    jzucker Supporting Member

    Messages:
    20,296
    Joined:
    May 20, 2003
    Location:
    Home of the ex-world champion Cavs
    [/i]

    Unfortunately not. :-( The mackie does have balanced inputs.



    I was talking about using a ground lift adapter. When I unplug the laptop so that it runs on batteries, some of the noise is reduced and several notebook users on the sonar forum reported reduced noise when they ungrounded their notebook computers.

    There's still some RF noise coming through. I suspect it'll occur anywhere in the house though.
     
  4. ari

    ari Member

    Messages:
    988
    Joined:
    Feb 26, 2004
    Location:
    St. Paul, MN
    I record with a laptop and can confirm that a plugged-in laptop can emit RF noise into the circuit, which can be picked up by any/all other musical equipment plugged into the same circuit. I tried plugging in the laptop into a different circuit and no noise from that source. Not sure if the ground lift will solve the problem, though. Ideally you wanna get an RF-filtered power strips -- one that really filters it, not just claiming to.

    ari
     
  5. jzucker

    jzucker Supporting Member

    Messages:
    20,296
    Joined:
    May 20, 2003
    Location:
    Home of the ex-world champion Cavs
    Can you recommend a specific brand of RF Filter?
     
  6. ari

    ari Member

    Messages:
    988
    Joined:
    Feb 26, 2004
    Location:
    St. Paul, MN
    Sorry, I can't, though if I were you I'd go with Furman stuff. I recall reading somewhere that many of the power strips that are sold in Wal-Marts and Targets that claim to have RF Filter don't work well. Furman, on the other hand, makes power supply stuff specifically for music uses, so I am guessing theirs work better.

    For me, putting the computer in a separate electrical circuit has cured my problem for now.

    Good luck!

    ari
     
  7. LSchefman

    LSchefman Member

    Messages:
    13,449
    Joined:
    Jan 4, 2002
    Jack, ground loops occasionally become little radio receivers.

    RF filters in power strips don't do a darn thing if you have a ground loop, and they tend to induce a different kind of noise into your audio.

    It's difficult to know what the problems are, exactly, from a distance, but you definitely have a ground loop somewhere. It's not a good idea to use ground lift adapters on a permanent basis, use it only to determine which piece of gear is causing the loop to occur.

    After you've determined the gear causing the loop, you have a few choices. Sometimes, you can lift the ground shield in the cable at one end. Rane, the equipment manufacturer, has a paper on how and when to do this, and if you email me your address, I'll be happy to send you my copy. You might also find it on their website. If this fix works, it's your cheapest bet.

    Ebtech is making a plug adaptor with a ground lift switch. It's not expensive, and may solve your problem. The nice thing is that you don't have to screw around cutting pieces out of any cables.

    A grounding block and grounding wire, properly earthed, may solve your problem, but you probably would find that to be overkill.

    Ebtech makes a small isolation transformer box, that eliminates ground loop hum. It runs about $70. You stick it between the offending pieces of gear.

    Ebtech also makes an 8 channel version of this device.

    You can buy an unbalanced-to-balanced line converter box. This way your gear audio connection is fully balanced, and runs at the same relative level. This sometimes solves problems. I have one you're welcome to borrow to try out, to see if it works. When you have a balanced run, cutting the shield at one end works better, if the box doesn't solve your ground loop. These run about $300-ish, but as I said, you're welcome to borrow mine to see if it works.

    I can't think of any other possible solutions.
     
  8. aeolian

    aeolian Member

    Messages:
    6,083
    Joined:
    Apr 5, 2004
    Location:
    Santa Cruz, CA.
    The way to solve a ground loop is to have a common ground point. A loop is created when the resistance to ground for one device is different that for another device. The differences in resistance create current flowing around the "loop" between the devices. Since most stuff references the signal to ground, the current flow gets added to the audio signal. When you run your laptop on batteries, it means that the only connection to ground is through the signal path, there is not a secondary path through the power supply. The other thing you do is remove what is probably a very noisy cheap switching power supply from your room. These both radiate interference and shoot noise back up the line. Some of this can be mitigated by making sure the supply has a good ground connection to the samepoint as the rest of the gear and some conducted noise can be filtered from the power cable. Given all the cables and connectors, equalizing the resistance to ground of everything might be tough.
    In extreme cases such as EMI test labs, everything has a high conductivity copper braid strap running from it's chassis to a common ground point. This is called "bonding".
     
  9. jzucker

    jzucker Supporting Member

    Messages:
    20,296
    Joined:
    May 20, 2003
    Location:
    Home of the ex-world champion Cavs
    There is in this case. Everything's in one power strip and it's grounded. Or do you mean something else?
     
  10. jzucker

    jzucker Supporting Member

    Messages:
    20,296
    Joined:
    May 20, 2003
    Location:
    Home of the ex-world champion Cavs
    Hi Les,

    I emailed you offline but didn't hear back from you. Please send me the link to the grounding info. I'd love to borrow your converter box. Let me know how you want to proceed.

    And as usual - Thanks for your help!
     
  11. EricT

    EricT Member

    Messages:
    1,010
    Joined:
    Nov 12, 2003
    Location:
    Norway
    Try plugging the notebook into another wall socket.
    I had the same problem as you, and changing the socket had the same effect as running on batteries, it removed almost all of the noise.
     
  12. jzucker

    jzucker Supporting Member

    Messages:
    20,296
    Joined:
    May 20, 2003
    Location:
    Home of the ex-world champion Cavs
    Thanks Eric. I'll give that a try.
     
  13. LSchefman

    LSchefman Member

    Messages:
    13,449
    Joined:
    Jan 4, 2002
    >>Hi Les,

    I emailed you offline but didn't hear back from you. Please send me the link to the grounding info. I'd love to borrow your converter box. Let me know how you want to proceed.

    And as usual - Thanks for your help!<<

    Hi, Jack,

    I just got your email and replied. What I have is hard copy on the Rane article, and I'm happy to loan you my converter thing. No problem.

    Just email me your snail mail addy.
     
  14. jzucker

    jzucker Supporting Member

    Messages:
    20,296
    Joined:
    May 20, 2003
    Location:
    Home of the ex-world champion Cavs
    Thanks Les.

    One more interesting thing. This morning when I turned my computer on, it was in sleep mode instead of being off. Therefore, there was still a connection to the firewire audio interface which is currently going into two channels of my Mackie mixer who's output is going to my monitors. When the computer "awoke" out of sleep mode, I could hear the high pitched whine of the hard disc spinning up through the monitors!
     
  15. LSchefman

    LSchefman Member

    Messages:
    13,449
    Joined:
    Jan 4, 2002
    Jack, I found the Rane articles on line, no need to wait for the mail, I emailed you the links.

    >>When the computer "awoke" out of sleep mode, I could hear the high pitched whine of the hard disc spinning up through the monitors!<<

    Yes, I have heard disks whine through my system as well. I don't know if the spinning disk creates RFI, or if it's just something microphonic.

    I try to isolate anything with a disk drive, but sometimes, it's unavoidable.
     
  16. MichaelK

    MichaelK Member

    Messages:
    6,479
    Joined:
    Jan 7, 2002
    Location:
    Fort Mudge
    After browsing the Rane site I downloaded a bunch of their articles. Some great stuff there!
     

Share This Page