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Discussion Starter · #1 ·
I'm trying to decide which settings are most appropriate for evaluating RT60 in my listening room. From what I gather, Topt is the preferred metric, however I'm less clear on whether I ought to use reverse filtering and zero-phase filtering.

The help box suggests that reverse filtering provides more accurate low frequency decay as long as you use Topt and not EDT. Would others concur with this assessment? Are there drawbacks to using reverse filtering with Topt?

As for zero-phase filtering, I was unable to find any advice as to when this option ought to be used. I'm assuming it corrects for phase differences between octave bands, but how exactly does that affect my evaluation of Topt? What are the trade-offs (presumably) involved with using it or not?

I'm just trying to give myself the most accurate perspective of the room's RT60 so as to make the best treatment decisions. For what it's worth, my room is on the smaller side (12x16x8 ft), so RT60 may not be applicable in the strictest sense of the term, but I figure it can still give me a decent idea of how decay varies between octave bands.

Thanks in advance.
 

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EDT = Early Decay Time, which is what happens in the first 10 ms after the impulse peak. It isn't relevant for RT60 values.

Reverse filtering isn't really needed unless you are examining behaviour with very low RT60 values, where the filter delay becomes significant. Unlikely to need it in a domestic setting.

Zero phase filtering was added to help people overlaying filtered ETC plots from different bands, it doesn't have much effect on the RT60 values in the regions where they are meaningful (above the modal range).

I'd leave both boxes unchecked.
 

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Discussion Starter · #3 ·
Reverse filtering isn't really needed unless you are examining behaviour with very low RT60 values, where the filter delay becomes significant. Unlikely to need it in a domestic setting.
Thanks, John. Just out of curiosity, how low are we talking before reverse filtering becomes relevant? My room is deader than most, with Topt ranging from .075 s to .166 s in all bands above 100 Hz and .203 s to .574 s below 100 Hz. Also (and I meant to ask this before but forgot), should RT60 be evaluated on a per speaker basis or with both speakers being driven simultaneously?

Thanks.
 

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Here are the different effects of the filters on a perfect impulse (which in theory has zero RT60, if that had meaning for such a response). Note that one-third octave filters have more delay than octave filters.

oct-normal.png

oct-reverse.png

third-normal.png

third-reverse.png
 
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