AFMG Network Forum

Lindsay Smith · Member

When doing STI calculations you have a choice of "Standard", "Male", "Female", "STIPa Male", "STIPa Female" and "RaSTI". All of these yield different STI values, some of them quite radical. In one room I get an average "Standard" STI of .403 while "STIPa Male" gives an average of .563. This is extremely significant.

One reason the values are so extreme is the speaker I'm using has minimal low frequency response. But what formula or weighting is being used to derive these values?

The manual and tutorial both devote space to explaining RaSTI and I understand it's limitations. What is not at all clear is what criteria are used with the various permutations of male and female. Does anybody have this information or can point to where I might find it?

Thanks.

Stefan · Member

Hi Lindsay,

the help files mention this in multiple places. STI calculations in EASE 4.3 comply fully with the standard IEC 60268-16:2003 for speech intelligibility. If you don't have EASE 4.3, upgrade now. It is free for all EASE 4.x owners: http://www.afmg-support.eu/AFMGDLPortal/Start.aspx

Generally, STIPA is prefered over RaSTI since the latter only employs 2 out of 7 octave bands. However, only STI uses all 98 MTF values compared to STIPA using 14 MTF values.

Ideally, you should be using the Male or Female weighting, depending on your speaker. Also make sure that if you use noise masking and/or signal masking according to the standard your loudspeaker output levels are properly set.

Stefan

Lindsay Smith · Member

Thanks for the response. Is there an updated version of the help file? I am using a full version of EASE 4.3.8.69 which appears to be the current version.

The only references to STIPa in the help file point you to the the STI portion of the appendix (I just did a full search on the Eaes43Help.pdf dated Aug. 4, 2009). There is no mention in the appendix of STIPa, only STI and RASTI. There are plenty of discussions in the literature of the difference between STI and STIPa, but a note in the manual on how EASE implements this would be helpful. It is also not clear what the non-STIPa male and female options do.

Thanks.

stevenliddle · Member

STIPA is calculated from 2 modulation frequencies in each of 7 octave bands - not the same frequencies in adjacent octaves. STI is all 14 modulations in 7 octave bands and RaSTI only uses modulations of the 500 Hz and 2kHz octave bands.