[panson]

How fractional octave (e.g. 1/12) smoothing is done in REW? Is it by a Butterworth filter or brick wall filter?

 

[JohnM]

Neither, it is a first order two-pass zero phase recursive filter.

 

[panson]

Is there any standard (e.g. IEC) for smoothing filter?

 

[JohnM]

Not that I could find.

 

[Toledo]

IEC 61260:1995 / ANSI S1.11-2004 if i`m not mistaken . Not shure if it was implemented that way in REW.

 

[JohnM]

IEC 61260 applies to the filters used for time signals, typically impulse responses - e.g. before calculating octave and third-octave RT60 figures. There doesn't appear to be any standard for the filter shape to be used in the frequency domain fractional octave smoothing filters.