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explaining cable phase

Discussion in 'Accessories / Connections' started by audiokid, Aug 5, 2010.

  1. audiokid

    audiokid Staff

    Could someone please explain the phasing?
     
  2. Boswell

    Boswell Moderator Distinguished Member

    Cables are all a matter of degree. If you have an electric guitar with low-impedance wound pickups or if you have an active pre-amp on your electric or acoustic guitar, the output impedance of the instrument is going to be relatively low, and the characteristics of the cable (when stationary) are not going to alter the sound very much. High cable capacitance, brought about either by excessive cable length or inherently high specific capacity of the cable, can cause the frequency of the resonant L-R-C of a pickup and cable to come into the top end of the audio spectrum, and this is where changing to a different capacity cable can appear to make a large difference to the sound. This is not a fault in the cable, but shows that you do have to be a little careful when choosing cables for an unbuffered guitar.

    If you have an acoustic guitar with piezo pickups and no guitar-based pre-amp, you have a high output impedance, and the cable characteristics can make a lot of difference to the sound. The basic rule here is to keep the length of cable from guitar to DI box or to pre-amp input as short as possible. Note that most passive DI boxes do not give an adequately high input impedance for piezo pickups, and so active DI boxes should be used when engineering this type of instrument when there is a long run from stage to mixing area.

    Cables subject to movement can appear add considerable noise to the signal they are carrying, as the change in capacitance caused by movement can translate to changes in voltage. In this instance, it's worth buying cables whose capacitance does not vary much as they are flexed, and this is the only part of that article that makes any engineering sense, even though it does not explicitly state this property being a necessity.

    At audio frequencies, the skin effect on cables is negligible. Cable capacitance and the way it changes as the cable is flexed is really the only parameter of concern.
     

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