RT60 and filters

[RobertoDiaz]

I have made some RT60 measurements, but when I change the order of the filter the decay time increases specially in low frequencies, why does it happens? how can I have a parameter to make a desision on what filter to use? thaks

 

[DanDan]

What Filter are you referring to?

 

[RobertoDiaz]

on the picture is indicated the filter section

 

[sam_adams]

The RT60 Graph section of the REW beta online help has some explanation of the filtering that should be applied. I'm sure @John Mulcahy will flesh it out a bit more when he has the time to explain the other filtering options.

 

[DanDan]

I was trying to take some of the load off, but the complexities of REW are vast now. I would just use the defaults unless there is some reason to do otherwise. Guessing, I would say the narrow filter, default, of course displays less energy than a wider one. Modes can mess up the notion of RT60 at LF. Take a look at the Correlation Factors, and better still the Waterfall to see if it messy down there. No pasa nada.

 

[John Mulcahy]

RT60 data can be shown in octave or one-third octave bands. The Filter order selection controls how steeply the fractional octave band filters roll off outside the band. The default order is 6 and that gives results comparable with most other software. Higher filter order makes the bands more selective, which can help isolate longer decays to a particular band, but increasing filter order also increases the delay of the filter itself. That can be mitigated by using Time reversed filtering or Zero phase filtering. I'll add a note on that to the help. Probably best sticking with the default 6th order filters and using the RT60 Decay graph for more detailed investigation of behaviour over narrower bands if required.