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

balanced/unbalanced

Discussion in 'Recording' started by Sidhu, Jul 25, 2004.

  1. Sidhu

    Sidhu Active Member

    what are the real advantages of having balanced inputs/outputs ??? will not the unbalanced outputs of a mixer (UB502, TS) into the unbalanced inputs of a Monitor (Event TR6, RCA) sound as good, as say their XLR counterparts ?? also for other connections, especially over rather short distances ??

    also why wud a small mixer like the UB series (Behringer), have balanced line inputs but unbalanced outputs ?????


    thank

    Sidhu
     
  2. BladeSG

    BladeSG Guest

    Balanced cables/IO's have the advantage of reducing ground hum because the sheild of the cable is introduced on either Pin 1 of an XLR plug or the sleeve of a TRS jack. IMO active monitors do benefit from having balanced cables as most of them are powered directly to 240V GPO, so the sheilded cable will reduce any grounding anomalies.
     
  3. Sidhu

    Sidhu Active Member

    i understand this of Balanced / Unbalanced IO

    correct me where i go wrong :





    take the example of the XLR cable. Say for a microphone.

    pin 1 sheild
    pin 2 hot
    pin 3 cold

    pin 2 carries the correct signal.

    pin 3 carries the reversed signal. (this reversal is done by the microphone itself. )

    pin 1 ground


    the mixer then reverses what it sees on pin 3. Thus bringing the siganl in phase with what is on pin 2.

    it then sums both the signals from pin 2 and 3. (in the process reversing the phase of the EMI and cancelling it)

    Also what role is then played the sheild.. Is it's purpose to first try and block any interference ? and if there is any, then the phase reversal trick comes into play ?

    I do not understand why it is said that balanced signals are louder than unbalanced ones. Or as to why is there an impedence difference between balanced and unbalanced inputs.

    eg. For unbalanced inputs the mixer has an impedance of 10 Kilo Ohms and for balanced it is 20 kilo ohms.

    please tell me if i am mistaken on any account.

    thank you

    sidhu
     
  4. bzbee

    bzbee Guest

    Longer cable runs are more susceptible to picking up noise. I'm not sure if this is true in general, but my long cables usually run into the mixer, eg mic or acoustic guitar, instead of out of the mixer, so maybe that's why the outputs aren't typically balanced.

    The shield is just for reducing EMI effect on the audio signal. Most of the crud picked up by the cable is passed through the grounded shield directly to earth ground and will reduce signal impairment. The principle behind the benefit of a balanced input is much akin to differential signalling in digital electronics. An analog (periodic) signal with amplitude +A and 180 degree phase offset is basically the same analog signal with amplitude -A and 0 degree phase offset. Say you have two wires running in parallel, carrying a signal of amplitude +A and -A, both with 0 degree phase offset. Each of the wires is subject to much the same environmental noise degradation N, with minor fluctuations represented by a delta_n term attributable to minuscule material and environmental differences, where delta_n is much smaller in magnitude than N.

    At the receiving end, the two signals received are:

    (1) +A + N + delta_n and
    (2) -A + N

    The mixer will find the difference between the balanced inputs represented by (1) and (2), which divided by a factor 2 gives A + delta_n/2. Note that the bulk of the noise represented by N is cancelled out, leaving the original signal A and the delta_n/2 term. As mentioned before, delta_n is very much smaller than the environmental noise N, giving you much improved signal to noise ratio which is critical in recordings. (A/N compared to 2A/delta_n)

    Other applications include noise cancellation headsets where onboard circuitry samples the ambient periodic noise (fans, 60Hz hum, etc) and produces the phase inverted "anti-noise" in real-time to cancel it out, leaving the original signal and dramatically diminished noise.

    HTH!
     

Share This Page