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Clarity Index calculation
PostPosted: Mon Dec 14, 2015 4:38 pm Reply with quote
cekcim
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Joined: 07 Sep 2015
Posts: 11
Location: Germany




Hi

I'm having a bit of an issue with the C50 and C80 measurements. In my IR, the first arrival is at around 30ms and at this point I get a certain Clarity value. When I use the 'move arrival to 0' function the value changes (goes down by about 8dB) However, using this automatic function, the first impulse is not exactly on the 0 point (there are about 0.4ms before first impulse). If I move it manually to the 0 position, the clarity index than goes back to the original calculated value. Can someone kindly let me know which way gives the correct result? I read in the manual that the energy is integrated for the first 50/80ms from the first arrival (based on the set detection threshold) so technically there's no need to move the IR to the 0 point right?

Thank you
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PostPosted: Tue Dec 15, 2015 2:38 pm Reply with quote
AFMG Pedro Lima
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Joined: 05 Jun 2010
Posts: 233
Location: Brazil




Hi Cekcim,

Yes, there is no need to move the IR to the 0 point. In the "Details" tab of the "Calculation > Arrival, C50, D/R, SNR" section, you can check the "Arrival" time in use for the C calculations (first item in the Data table).

But if you want to move the IR to the beginning it should be OK too, as long as you donīt "cut" to much of the IR beginning. Be attentive to the criteria used for the "Cyclic Move". In this case the Arrival will display a value of 0 ms (or so) and if you did it right, the C values should match (you might see 0.1, 0.2 dB of difference if you cut a bit of energy).

But indeed a drop of 8 dB is too much. Check if you are not moving the IR too much so that considerable energy is going to the end of the IR. Or if the calculated Arrival shows an adequate value (you can inspect the IR with the mouse, look for the energy arrival time and compare with the value in the Arrival field).

If you like, you can send me the IR so I can take a look.

HTH.

Kind Regards,
Pedro
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PostPosted: Tue Dec 15, 2015 2:48 pm Reply with quote
AFMG Pedro Lima
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Joined: 05 Jun 2010
Posts: 233
Location: Brazil




One more thing, you can also check the Arrival Time threshold in the Options menu > General.
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PostPosted: Mon Dec 28, 2015 1:32 pm Reply with quote
cekcim
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Joined: 07 Sep 2015
Posts: 11
Location: Germany




Hi Pedro,

Thanks a lot for the information, it was very helpful.

All the best!
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Clarity Index calculation
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