Confused about RT30/RT60 Values - Home Theater Forum and Systems - HomeTheaterShack.com

Old 06-12-14, 11:57 PM Thread Starter
Shackster
mparsons99

Join Date: Oct 2008
Posts: 6
Confused about RT30/RT60 Values

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
mparsons99 is offline

Old 06-13-14, 07:00 AM
Elite Shackster

Join Date: Mar 2009
Location: Michigan, USA
Posts: 1,368
My System
Re: Confused about RT30/RT60 Values

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.
jtalden is offline
Old 06-13-14, 10:49 AM Thread Starter
Shackster
mparsons99

Join Date: Oct 2008
Posts: 6
Re: Confused about RT30/RT60 Values

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

Last edited by mparsons99; 06-13-14 at 11:03 AM. Reason: Additional information
mparsons99 is offline
Old 06-13-14, 12:20 PM
Elite Shackster

Join Date: Mar 2009
Location: Michigan, USA
Posts: 1,368
My System
Re: Confused about RT30/RT60 Values

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.
jtalden is offline

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