# STI from REW



## Zanyar (Dec 9, 2016)

Hi

Is there any way I could use REW to measure the Speech Transmission Index (STI) of a room?

STI measures speech intelligibility and is based on the Modulation Transfer Function (MTF) of a system (a room in this case). The idea of STI is to send a signal (usually a pink noise) which is filtered to have the spectrum of human speech. The signal consists of 7 octave bands from 125 to 8000 Hz. Each octave band is modulated by 14 one-third octave-wide frequency bands starting from 0.63 Hz to 16 Hz, resulting in 98 MTFs. 
Thankfully, MTF for each octave band and modulation frequency can be derived from the impulse response using the following equation (ICE 60268-16):

mk (fm) = [|∫hk (t) e ^(-j2╥fmt) dt|]/ ∫ hk (t)^2 dt

Both integrals are from 0 to ∞. 

where, 
hk (t) is impulse response of octave band k; 
fm is modulation frequency.

This is the theory, but I have no idea how to implement that. Your help is highly appreciated. 
I know the equation looks messy, but I do not know how to type it here correctly. If possible, I can post a picture of the equation in the right format. 

Thank you!


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## JohnM (Apr 11, 2006)

REW can measure the impulse response but does not calculate STI. You would have to export the impulse response and carry out the calculations yourself, or try ARTA.


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## Zanyar (Dec 9, 2016)

Dear John, 

Thank you very much for your prompt response. I do appreciate your suggestion on using ARTA. 
Forgive my ignorance, I wonder how can I export the IR? I was thinking of using MATLAB to do the calculations but was not sure how to export the IR into it. 

Thanks.


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## JohnM (Apr 11, 2006)

From the File menu you can export the IR as a WAV file or as text, with a delimiter that can be selected from the export menu. Text export is handy if you want to import to a spreadsheet. For matlab you can use the audioread function to import the WAV file data - the peak is 1 second in from the start of the file. Select the option to normalise the IR when you export it and use 24-bit data.


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## Zanyar (Dec 9, 2016)

Thank you so much! You are extremely useful and kind. I wish I had known you sooner.


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