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I don't understand mic attenuator switch

Discussion in 'Pro Audio Equipment' started by cmoseman, Nov 15, 2005.

  1. cmoseman

    cmoseman Guest

    I have an AT4033a/SM, with the -10dB attenuator switch. I am recording vocals, and I don't understand if I should be using the pad switch or not.

    The manual says this for Maximum Input Sound Level:

    145 dB SPL, 1 kHz at 1% T.H.D.
    155 dB SPL, with 10 dB pad (nominal)

    So I suppose vocals aren't really going to go 155dB SPL (?), so I would NOT engage the -10dB pad? is this correct?

    Or can vocal plosives get up there, and I 'should' use the -10dB pad?
  2. lgabiot

    lgabiot Guest


    You have indeed to consider if the sound you will be recording is about to reach that level, but there is another thing also to check to make your decision:

    What is the output signal delivered by your mic at thoses high levels? (you can calculate that by looking to the sensitivity rating of your mic) It might be possible that at high SPL level, the output of your microphone might be clean, but so hot that your preamp can't handle it. In that case also the -10 dB can help.
    (a quick rough calculation, might be wrong because it's a long time I didn't do this... so correct me in that case: AT4033 sensitivity:
    25.1 mV re 1V at 1Pa (94dBSPL). So at 145 dBSPL the mike will output: 145-94=51; 51/6=8.5; 2^8.5=360; 0.0251*360=9V which mean a 9v RMS output... can your preamp handle this?)

    Voice can be very loud, (opera singers for instance), and normal SPL measurement are done or recalculated to 1 meter, and are approximately RMS (correct me here, as my way of putting it is quite bad). So if your mic is very close of a sound source, it can receive a SPL much more high than "book described" SPL (which are meant "at one meter").

    So I don't have a definite answer on this, from the theory point of view, exept that it will be easy by listening to hear if it's better to use that -10 pad.

    Best regards,

  3. moonbaby

    moonbaby Mmmmmm Well-Known Member

    Realistically, you will more than likely not need to pad the mic for a vocalist. That isn't absolute, as there are some real screamers out there. But 155 dB is a real high SPL. As for the plosives, they are better controlled by the 80 Hz. highpass filter (and a "popper-stopper"). Great mic...enjoy!

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