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Confused by microphone cables...

Discussion in 'Accessories / Connections' started by PhilReeve, Nov 19, 2007.

  1. PhilReeve

    PhilReeve Active Member

    I've got a Behringer XM8500 mic that I'm using to record straight in to my PC's standard mic input. I bought a balanced mic cable with it just so that in future if I changed to a balanced system I'd have the right cable (my soundcard's input is not balanced).

    Anyway, I get loads of noise using the balanced cable, and drastically less using a different, unbalanced cable - can anyone explain why this is?

    I'm using Sound Forge by the way, with the input set to use the left stereo of the soundcard's mic input - right is silent if I try to use that and mixed (stereo) is the same as the left, as far as I can tell.

    Thanks,
    Phil
     
  2. Cucco

    Cucco Distinguished Member

    The mic input on soundcards is set up to handle pre-polarized computer mics which have a load of gain built right in. That means, to get the amount of sound from a "mic level" signal, you'll have to boost the gain a bunch - hence the noise.

    Computer soundcards are not designed for use with "real" microphones. You'll need to get an interface - you can get stuff from M-Audio, Edirol, Alesis, PreSonus and others for a VERY reasonable cost nowadays.

    Also, you're only getting mono because you're only using one microphone. Stereo requires the use of two mics or a mic and another source.
     
  3. PhilReeve

    PhilReeve Active Member

    I wasn't trying to get stereo - just point Sound Forge at the left stereo, in the hope that it would use the Screen and Hot connections from the mic.

    The unbalanced cable basically connects both Screen and Cold pins from the XLR on the mic to the Sleeve on the 1/4" jack and the Hot to the tip, which seems to have the effect of not producing all that noise.

    I'm happy to use unbalanced cables and put up with the noise, I just wondered if anyone could explain to me what's going on with the mic signals and whether it's good practice.

    Thanks for the tips anyway - I might look in to those interfaces.

    Phil
     
  4. moonbaby

    moonbaby Mmmmmm Well-Known Member

    Cucco told you. The mic you have is not properly matched to your sound card. You need to have a preamp that was designed to handle a balanced source. So, NO, what you're doing is not "good practice".
     
  5. PhilReeve

    PhilReeve Active Member

    OK, but I'm skint at the moment so the cheapest option is the best one - I can put up with a bit of noise, we're only going to be recording a band practise.

    Will having the Screen and Cold pins mixed in this way have a bass-cancelling effect on the mic signal though? That's all I'm really worried about.
     
  6. Cucco

    Cucco Distinguished Member

    There's nothing wrong with attaching the screen and the cold in this application.

    Don't try to do it if you plan on running phantom power up the line any time soon. You might want to try hooking the cable up like that to a ribbon too...should be fun.
     
  7. PhilReeve

    PhilReeve Active Member

    OK, thanks, I'm happy to go with that then.

    Could you explain how a balanced cable works though? I've read through the Wikipedia page and I'm none the wiser...

    If the hot and cold carry identical but inverted signals... and are then 'added' at the other end, doesn't this not only cancel out noise, but all of the signal as well?
     
  8. bent

    bent No Bad Vibes! Well-Known Member

    No, the signals are 180 out down the line. When they hit the balancing amp they are reverted back into phase, which in turn flips the noise on the wires to 180 out - the noise gets flipped out of phase at the input and is therefore canceled.
     
  9. PhilReeve

    PhilReeve Active Member

    OK, I think I've just about got it - but web pages have different ways of explaining it.

    If you say they're 180 degrees out - do you mean that one signal is time-shifted? or that it's kind of negative instead of positive?

    And is this right: because the balancing amplifier only considers the differences between the two signals, noise is not detected because it has a cancelling effect on itself when the two signals are added?

    Sorry for going on about it, but I want to understand this properly.
     
  10. bent

    bent No Bad Vibes! Well-Known Member

    No.

    Yes

    Yes.

    There are many ways to make a balanced interconnect, but you are getting the basics down - good job!
    :cool:
     

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