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Cable length effecting recording quality

Discussion in 'Accessories / Connections' started by mdanser, Jul 19, 2009.

  1. mdanser

    mdanser Guest

    I am tracking a few songs for the church I work at and to save costs, we are doing all the recording in house. We have a worship center that has a custom-install snake through conduit in the wall with several parallel termination points. Where I was planning on setting everything up to be recorded was either on stage or around the various areas of the large worship room (2500+ sqft) In total, I imagine there is 200-300 feet of cable before it would get to our production room, which is where I would set up my DAW/monitors.

    Would this effect my recording enough to be a concern? I know that with typical long cable lengths, the high frequency resistance starts building up significantly. What is the general consensus on max cable length for recording?
     
  2. Kev

    Kev Well-Known Member

    welcome

    good quality star quad cable
    200-300 ft of cable is ok

    all things considered
    and yes you probably could set up a test and show there is a difference with a shorter cable

    the advantages of having all the gear in the production room are obvious and some may advise to have the Mic-pres on the floor
    ...
    you can still do this with the snake
    but it is best not to mix line levels with mic levels
    SO
    two quality smaller snakes may be better than one larger one
    one for line and one for mics only
    don't skimp on the #2 snake so that BOTH can be used for mics
    they can also be directed to different parts of the floor
    ...
    just a thought

    expect to pay a little more for a top quality snake with good connectors and good soldering

    concert halls are big places so you are not doing anything that hasn't been done many times before
     
  3. Boswell

    Boswell Moderator Distinguished Member

    200 ft of good quality balanced cable should not be a problem when used with dynamic mics. With capacitor (condenser) mics, it will depend on the type of buffer used in the mic whether it has stability problems when driving that amount of cable capacitance, but if you stay away from cheap Chinese types, you should be OK.

    In either case, a touch of EQ (1-2dB at 10KHz) will compensate for H.F. losses due to cable capacitance.
     
  4. BobRogers

    BobRogers Well-Known Member

    Boswell- Could you please explain in a little more detail why the condenser has more problems with the cable capacitance than a dynamic. Thanks.
     
  5. Cucco

    Cucco Distinguished Member

    No matter how I do the math, I can't find a 2dB dip in the audible frequency band for a cable length of less than 500 feet. Beyond that, it starts to heavily depend on the type of cable, etc.

    FWIW, I've done shows where I'm running through nearly 1000 feet of cable with no significant issues. I did notice a slightly dull sensation, but only mildly.

    Cheers-
    J.
     
  6. TheJackAttack

    TheJackAttack Distinguished Member

    That dull sensation...did it have to do with the conductor?
     
  7. Cucco

    Cucco Distinguished Member

    You know him??
     
  8. TheJackAttack

    TheJackAttack Distinguished Member

    I know the part where you get done talking to him and you go and beat your head against a wall! Brick walls make a sharp sensation though.
     
  9. MadMax

    MadMax Well-Known Member

    +1 on what J and kev said.

    I routinely run 300 ft trunks plus 20 ft fans. There isn't anything to worry about until you get over 500 ft... and even then, the loss issues don't become a practical issue until over 1400-1500 ft. of a decent quality snake.
     
  10. Boswell

    Boswell Moderator Distinguished Member

    There are several possible effects of long (high capacitance) cables:

    (1) The cable capacitance reacts with the output resistance of the microphone, forming an R-C low-pass filter. The relevant cable specification for this effect is conductor-to-screen + 2*conductor-to-conductor capacitance, amounting to typically 85pF/ft. The roll-off filtering is a linear effect and, in principle, can be corrected if necessary by applying EQ (but see below).

    (2) The active followers used in some condenser microphone designs pull only in the positive direction, and rely on resistive discharge of the cable capacitance for the negative direction. Also, phantom-powered followers are inherently current-limited, and can show slew-rate limiting. The result of these design shortcomings is that high-amplitude transients suffer non-linear distortion. The relevant cable specification for this effect is the conductor-to-screen + 2*conductor-to-conductor, typically 85pF/ft.

    (3) I have seen the active circuity in some condenser microphones become unstable when connected to a high-capacitance cable. The result is high-frequency (supersonic) oscillations at the microphone output that not only affect the quality of the transmitted audio, but can upset the input stages of a pre-amplifier. The relevant cable specification for this effect is the conductor-to-screen + conductor-to-conductor, typically 55pF/ft.

    For a 1000ft run, the above capacitance numbers can be read as nF, and the effect of the linear R-C roll-off with a 200 Ohm microphone is a 3dB point at 58 KHz, 1dB at 29KHz. I should have worked through the numbers earlier, as I was over-pessimistic in saying previously that you might need 1 or 2 dB of EQ boost at 10KHz.

    Note also that dynamic mics (moving-coil and ribbon) usually have no followers or other active circuitry, and so do not suffer from effects (2) and (3). I know there are some ribbons (e.g. Royer) with internal phantom-powered pre-amps, so those behave as condensers in this case. I should add that the only oscillation problems I have seen have been with a cheap Far-Eastern-made condenser, and the audio under those conditions was so obviously distorted that you would stop to investigate what was wrong before doing any recording.
     

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