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meters, tape, desks & levels

Discussion in 'Recording' started by Caldusofcot, Feb 9, 2006.

  1. Caldusofcot

    Caldusofcot Guest

    Help we are confused!

    We are set to mixdown down several tracks through our Spirit desk onto 456 tape running on our Revox. What is confusing me is levels. The Revox has been serviced and calibrated for the 456 and has no meters - quite common for a PR99. So I record three reference tones at our 0 on the desk which is +4 dbu. When I feed in a sine wave at 0db with no gain from the oscillator it appears as -3dbu on the Spirit meters. Do I adjust this up to the 0 @ +4dbu level ? When I recorded three tones onto tape at -3 then playback through the desk it shows a level of +3 above 0 @ +4dbu.
    Whats does all mean or do I just ignore it and record the darned thing.
    Tape does sound nice though....

    Cheers
     
  2. Kev

    Kev Well-Known Member

    no don't ignore it

    if you are putting some tones on the tape you need them to be just as you descibe them on the tape label

    the 3dB thing could be the pan rule for the desk ... sorry I don't know that desk ... and I don't know how the tone is applied to the output bus

    it might be easier to start with an external tone and then measure it with a passive VU meter just to be sure of what you have

    I have a simple chart if you have a DVM to double check things
    (Dead Link Removed)

    The main point once it is all done,
    is that the labelled tape with a 0dBu or +4dBu test tone
    does playout at the desired level.
     
  3. Caldusofcot

    Caldusofcot Guest

    Got your Chart

    Hi Kev,

    Got your chart, I have a digital test meter but no external vu other than the desk one. How do I use your chart with a volt meter ?
    the tone is not from the desk but from an audio oscillator programme on a laptop fed into a mixer channel set at 0 gain.
    Thanks for replying.

    Cheers

    Andrew
     
  4. Kev

    Kev Well-Known Member

    set DVM to volts AC
    and have tone generator set for sine wave
    try do frequencies less than 1000Hz and more like 100Hz cos some meters get it wrong for the higher frequencies

    measure volts across pins 2 and 3
    0dBu (unterminated) = 0.7746 Volts AC rms
    +4dBu = 1.2277 Volts AC rms

    +4dBm (600 termainated)
    means the output can put the 0.7746 Volts AC rms on the 600 ohms load

    SO
    tone generator creates 0.7746 Volts AC rms
    while tone is running and being measured connect it to the input.
    If the level drops you know you have a load.
    This may mean you need to increase the level of the tone generator.

    You now know you have +4dBu going into the desk.

    Move the DVM to an output ... check that 0 gain and faders in the 0 position actually put +4dBu on an output.

    Repeat the above method to check if the Tape Deck loads the Desk Output.

    The rest is in the hands of the calibration of the Tape Deck itself.
     

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