1. Register NOW and become part of this fantastic knowledge base forum! This message will go away once you have registered.

Noise

Discussion in 'Recording' started by Gpp, Sep 27, 2016.

  1. Gpp

    Gpp Active Member

    Hello,

    I'd like to have some advice about how to avoid, during the field recording, the mechanical noise due to the contact of the wires of the mics hiting each other or maybe hiting the grip holding the microphones.
    Can I find in commerce a special grip for the cables? How do you usually solve this problem? I try to be careful to any contact, but the result is always disappointing. The cable I'm using are 3 mt long, part of the cable is rolled, so they don't dangle.
    Any suggestion?

    Thanks,
    Gpp
     
  2. pcrecord

    pcrecord Don't you want the best recording like I do ? Well-Known Member

    I'd say get a better cables.
    I am assuming you are using a standard XLR microphone cable. If not, please do say what it is.
    Usually a good wire sheilding will prevent noises to be introduce in the signal.
    Getting noises by tapping a cable with your finger or with another cable is a good sign the cable is very cheap.
    But I could guess that if the mics you use to record in the field are very quiet and you need to push the gain way up on the preamp. . ,
    I honestly don't know if it would make those noises with any cables..

    Let me know what mics, preamp and recorder you are using.. it's gonna clear up the picture ;)
     
  3. dvdhawk

    dvdhawk Well-Known Member

    I would agree with pcrecord on your situation. The kind of cable handling-noise you are describing is minimal in most modern low-impedence microphone cables of reasonable quality. I've experienced that more often in old, stiff, high-impedance cables.

    Can you confirm that the wires are soldered to the correct pins?

    On an XLR cable, the shield should be connected to Pin #1, and whatever color is soldered to Pin#2 on the female, should be soldered to Pin#2 on the male end. The same goes for Pin#3. I've seen brand new cables that were wired incorrectly - somebody's first day at the factory I assume.

    A simple plug-in cable tester like shown below, can test for continuity (or shorts) and crossed wires, but not whether they got the shield on the right pin throughout.
    Tester.jpeg

    The same would be true for an ohm-meter / multi-meter as shown below, which would also only indicate continuity (or shorts) and crossed wires.
    MM.jpeg

    So although both kinds of testers are useful to some extent, if the person who made the cables soldered them consistently wrong on both ends, the testers wouldn't help spot the problem. The only way to be sure the shield is on Pin#1 is by giving it a visual inspection. And don't forget the male and female are mirror-image to one another. You have to look for the tiny number imprinted on the connector.


    Here is one manufacturer's explanation for what causes handling noise in cables and how they prevent it - Particularly Section #3 on Discharge.
    [Source: Elite Core Audio - Tour Grade Mic Cables Page] PLEASE NOTE: They are trying to sell you their mic cable, but the information presented seems valid enough and relevant to the conversation. If any of the in-house engineers disagree, I'll gladly remove it.

    Conductive PE Layer:

    The magic of the CSM2 cable is found on the outside of the red and black inner cores. It’s a refined thin layer of conductive PE. Yes, that’s right, it’s a layer of thermoplastic polyethylene that has been precisely blended with carbon fiber to create a conductive layer that is perfectly snug around the red and white inner cores. This layer is key to the CSM2 cable. These days, there is an extreme amount wireless noise (from wireless mics, IEM transmitters, wireless DMX devices), electromagnetic noise (from power cables, lighting ballasts and moving light motors), and just plain abuse (from people and casters!) in the world of entertainment sound, lighting and video. The CSM2 cable provides an extra layer of shielding with the conductive PE. This layer serves three purposes. When selecting your cable, it’s important to consider whether these three issues are some that you deal with.

    csm2_5_1.jpg

    (1) Immunity from outside EMI and RF interference. Since the PE is conductive, it provides an additional layer of shielding from RF and EMI noise that is being emitted from many sources on all stages. If your stage has wireless sources or electricity, this is critical.

    (2) Containment of any EMI transmission that your signal may emit. The days of microphone cables only carrying natural voices or analog instruments are long since over and gone. Today’s production stages are full of tracks, clicks, loops, and many other loud and potentially troublesome signals. It’s important to keep those signals to themselves. The conductive PE on our CSM2 cable does just that. If you’re anything but an all-natural bluegrass band, this is critical.

    (3) Discharge of piezoelectric static and noise. When a mic cable gets knocked around by an active vocalist, or stepped on by an active stage hand, something troubling happens. There is a triboelectric effect that occurs when the insulators are pressed and misshaped, that causes a slapping, or thumping noise. This causes a piezoelectric discharge that ultimately functions as a crude transducer. Granted, the signal level is very low and the resulting noise is very minute, but this noise can still cause problems because it is intensely amplified once it reaches the preamp in the mixer. The layer of conductive PE we have added serves to drain off this static and eliminate the potential of handling noise. The net result is a dead quiet cable. If you have humans using your mics and cables, this is critical for your application.
     
    pcrecord, DonnyThompson and kmetal like this.
  4. DonnyThompson

    DonnyThompson Distinguished Member

    Great post, Hawk. ( @dvdhawk )

    (@audiokid )
    This should be a sticky.

    I'd do it myself, but I lack the power... I lack "The Force".
     
  5. rmburrow

    rmburrow Active Member

    dvdhawk.... Very good post on mic cable pin out. The shield always goes to pin 1 on the XLR. Normally, I connect the red (audio +) to pin 2, and the white (audio -) to pin 3. This may be part of an old IEEE standard.

    My regular line of work is with RF...and RF mitigation. The modern stage is replete with many digital devices (MIDI, electronic organs, other instruments, etc.) authorized under Part 15 of the FCC rules. The emission and conduction limits for these devices is defined under Part 15. Several years ago, I encountered a high level of RF from a MIDI device (on a pipe organ) that emitted a rather high signal in the 1.5 MHz range that was intense enough to get into a mic cable. Note that RF interference ("RFI") is both emitted and conducted. It is radiated by cables connected to the offending device (cables become an antenna), or is conducted back into the AC power line. I use a spectrum analyzer to obtain a "signature" of the venue and look for signals from offending equipment or nearby radio transmitters (stations)... The FCC won't allow equipment exceeding the Part 15 standards to be sold in the USA..but the quality of shielding inside the equipment is a different matter. Some of the shielding is no more than flimsy foil, or sprayed on the inside of the plastic case. The days of the heavy metal chassis needed to support transformers, etc. is mostly gone. Drop one of those digital "boxes", or open it up to fix something, disturb the shielding, and the device suddenly becomes an emitter.

    Corrosion is another interesting problem. Female connectors especially. Metal oxides (like copper) make good rectifiers. Any significant RF signal coupled into a cable connected to a corroded connection may create noise that may be difficult to locate.

    Audio rectification of various RF signals is perhaps the oldest mode of interference out there. Rectification of AM signals from a nearby radio station is well known, even from the tube days. Solid state devices...remember the crystal radios? Any good p/n junction in a solid state device will rectify RF...

    I have found that the plug-in Hum-X filters work well on conducted interference. They are around $65 each from B&H in New York.

    If you know the geographic coordinates of a venue, the venue can be checked for nearby radio and TV stations on the FCC web site www.fcc.gov/mb.... look for AMQUERY (AM stations, FMQUERY (FM stations), and TVQUERY (TV stations)...use a search radius of 3 km (2 miles)... Audio equipment (especially PA, etc.) installers should check for nearby radio or tv stations before bidding a job.... mitigating RF may be costly....

    All I am saying is VISUALLY open up the XLR connectors on your cables periodically, especially if they are used for rough field recording, or have gotten wet for any reason. Make certain the shield connection to pin 1 is securely soldered on both ends. Then make sure that there is no phase reversal in the cable....
     
    dvdhawk likes this.
  6. dvdhawk

    dvdhawk Well-Known Member

    Thanks Donny. (@DonnyThompson)

    In what little spare time I have, I've been percolating on a page, or series of pages, with this kind of basic information on it, to help people choose the right cables and connectors for their specific job. In my travels doing installations and service-calls, I've seen a lot of different ways for folks to sabotage themselves.
     
    pcrecord likes this.
  7. dvdhawk

    dvdhawk Well-Known Member

    Given the insulation colors of red and white, I'd do the same, but I see more and more cables with different colored insulation combinations in them. I've thought it must be the result of different standards around the world, and more and more imported wire. Since the OP seems to be from Italy, I didn't want to assume they would have red and white to work with.

    Churches are notorious for letting their amateur electricians solder their snake or mic runs to save a few bucks. Unfortunately, they will sometimes wire the XLR as if it were an AC cable. They'll put the shield on Pin#3, because it's in the middle and that's how they would make a power cable. It will pass signal, but you can imagine (or almost certainly have encountered) the resulting noises. And/or they will forget, or fail to realize, the connectors are mirror-image and often flip 1 & 2. Then they'll do any combination of those things wrong and connect something that requires phantom power and all manner of unpleasant and dangerous things can happen.

    Sometimes they'll mistakenly apply the US standard for high-voltage wiring, and use the black wire as the 'hot'. Again, not the end of the world if they're consistent on both ends, but bad news if they're just 'fixing' one end of a speaker cable.

    @rmburrow, do you recommend anything that would be better than Caig DeOxit for cleaning up oxidized / corroded contacts?
     
  8. rmburrow

    rmburrow Active Member

    dvdhawk...Don't know if you can get it anymore, but Cramolin is good on contacts...Use sparingly, a bottle lasts for years.
     
  9. dvdhawk

    dvdhawk Well-Known Member

    I was under the impression that Cramolin wasn't available here anymore due to tightened EPA standards, freon etc.
    Here's a page posted on Pitt's site with some "history"(?) that they admit is hard to verify, but seems pretty plausible.
     
  10. Kurt Foster

    Kurt Foster Distinguished Member

    LPS 1

    recommended to me years ago by Michael Gore from Analog Rules. he was my sevice tech when my studio was running. over 8 years and he never steered me wrong. smart guy!
     
    pcrecord likes this.
Similar Threads
  1. mahatma
    Replies:
    0
    Views:
    414
  2. jakep
    Replies:
    0
    Views:
    714
  3. audiokid
    Replies:
    0
    Views:
    393
  4. audiokid
    Replies:
    0
    Views:
    538
  5. audiokid
    Replies:
    0
    Views:
    670
Loading...

Share This Page