# Confused about RT30/RT60 Values



## mparsons99 (Oct 9, 2008)

Hello,

Fairly new to REW. 
I've made some impulse response measurements and imported them into REW. 
Am I right in assuming that REW is giving me just the RT30 value and if the r value is close to -1 then I can just extrapolate to get the RT60 value. In this case assuming the line is straight. Can I just double the RT30 value or do I have to calculate it using the slope?

In other words all this talk of RT60 is really talk of RT30??

Matthew


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## jtalden (Mar 12, 2009)

There is a section in the "REW help" describing these decay rate estimates.
My limited understanding is that RT20, RT30, and Topt are all estimates of the time for a 60dB decay. They just use different segments of the IR decay to make the estimate. The segments used are defined in the help section.


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## mparsons99 (Oct 9, 2008)

O.K..thanks for the reply...I understand that the RT30 value is measuring from -5 t0 -35 dB or the rate of decay but do I have to extrapolate to get RT60?..i.e do I pretty much double the RT30 time?

My confusion comes from the 'Filtered IR ' screen. The calculation screen indicates that the RT30 time for this room is 1.19s. But if I look at the Plot with dB FS it looks like the impulse falls to 60Db in this time...the calculations and the graph seem to be at odds...

Matthew


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## jtalden (Mar 12, 2009)

I can only say that my understanding is that each of the estimates is an estimate of the T60 time; all 3 are estimates of the same value. That is, there is no need to extrapolate for the value. REW already did that.

Your situation/question suggest there is reason in your data that makes that interpretation seem questionable. I do not see the same concern in my data. 

Maybe if you post the .mdat in question, someone here may be able to assist. I will help if I can, but it may not be me as I have little experience with this aspect of audio analysis.


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