Measurement Clipping, 0db Headroom

Discussion in 'Official REW (Room EQ Wizard) Support Forum' started by kolabıuzlu, Apr 8, 2019.

  1. kolabıuzlu

    kolabıuzlu New Member
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    Hi. First of all, thanks for this great software! I have a small issue and I’m wondering why? I’ve made soundcard calibration with success. Checked levels.. Calibrated SPL Meter shows 75 db when -12dbfs signal is on. Dayton Emm-6 mic shows -18db in “Check Levels” tab. I think everything is fine. But when I click ‘measure’, there is no headroom left. It’s 0 db and clipping message shows up. I need to lower my mic input until it shows -25, -26db in “check levels” (which is very low I think), in order to gain some 1-2 db headroom while measuring. With -18db mic setting, ideally I should have around 6db headroom. Can you please help? Best regards.
     
  2. John Mulcahy

    John Mulcahy REW Author

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    -26 dB is not particularly low, the headroom you need will depend on how high the levels get when passing through the room's resonances. Make a measurement with the mic gain low enough to avoid clipping and post it here, then we can check if all looks OK with it.
     
  3. kolabıuzlu

    kolabıuzlu New Member
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    Here is my measurement file attached. It's the measurement of left speaker. SPL is around 76.5 db. Mic level is around -24dbfs in "Check Levels" window. Not clipping, there is around 5 db headroom. Is everything OK? Thank you very much for your help. With my best regards.
     

    Attached Files:

  4. John Mulcahy

    John Mulcahy REW Author

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    Looks good, about 80 dB signal to noise in the impulse response which is excellent. Looks like it was very noisy before the measurement started though, based on the captured noise floor which is shown on the Distortion graph:

    distortion.png
     

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