Is my measurement incorrect (mdat attached)?

vanzeng

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Jun 7, 2019
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4
Hi guys,

I used REW to test my room. When I asked for help for acoustic treament later, one of my friends told me my measurement method might be incorrect for the reason that both the impulse responses and waterfall plots don't look plausible, so the mdat might be invalid for analysis.

Here I uploaded my mdat file and I introduced my method. And I need advice to see if my measurement is valid.

My soundcard: RME Fireface UCX (using its internal mic preamp)
Steps.
1. Peference-Soundcard page. Use a TRS cable from soundcard Output 1 to Mic/Line Input 1. Phantom power off. Soundcard Output Volume = 0db, Soundcard Mic/Line Gain = 0db.In Preference-Soundcard page during the calibration, The output and input level are alomost both equal to -6db.Calibrate. Unplug the TRS cable.
2. The SPL Meter page.Press Calibrate. Adjust Soundcard Output level to -32db, so that my external SPL meter (with no connection to the computer) reads 76db. Type 76db in the calibration pop-up window.
3. Plug Behringer ECM 8000 to Mic/Line Input 1. Phantom power on.
4. The Measure page. Press Check Levels. Adjust Soundcard Mic Gain to +45db so that REW Input level read around -18db.
5. Start Measuring.I used Left/Right only signal during the measurement.


It seems that my mdat file could not be upload (6MB). Any other way to upload my mdat?
 

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vanzeng

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Jun 7, 2019
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All sounds good. You probably can't attach the mdat yet as this is your first post.
Thank you John. My friend said both the impulse responses and waterfall plots don't look plausible. Here I attached my IR and waterfall plots.
 

John Mulcahy

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Apr 3, 2017
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1,620
The images look normal, though the vertical span of your waterfall plot is a bit small, would usually present them with a vertical span of around 60 dB. Try attaching the mdat again.
 

Ultrasonic

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Apr 21, 2019
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My AV System  
Preamp, Processor or Receiver
miniDSP 2x4 HD
Main Amp
Bel Canto Evo4 gen2
Universal / Blu-ray / CD Player
OPPO BDP-83
Front Speakers
Meadowlark Shearwater Hot Rod
Subwoofers
BK Monolith
Hi John,

It's my fault this is being queried. I was responding to the following Gearslutz thread, which also includes the mdat file if you want to see it.


I thought the waterfall plots looked wrong as the long high frequency decay times didn't match the photo of the professional looking studio shown in the thread, being much longer than in my own domestic room. However, reading back I see that although bass-traps had been installed there is actually no other absorption in the studio, so perhaps it is real.

I also thought the shape of the IR looked odd to me, and not unlike some where timing errors have been assumed. If you say it's normal then it is though, so apologies I was wrong there @vanzeng .
 
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akebrake

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Jun 14, 2017
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Hello vanzeng and John!

May be I can help
Sorry, I missed vanzeng latest uploaded mdat (on GS Forum).
(Seems you have solved the soundcard issue).

22604


I am still curious what was the problem.
John, would you mind take a look? Here is a link to the old and new mdat.

Best regards

Ake
 

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John Mulcahy

REW Author
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Apr 3, 2017
Messages
1,620
The "close sit" measurement has a room measurement loaded as a cal file instead of a soundcard measurement, that needs to be removed.
 
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