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Evaluating STI

After a measurement has been recorded or imported, click on the SPEECH button to view the speech intelligibility parameters. Multiple speech and noise scenarios can be defined and evaluated here.

Speech/Noise Not Defined

The default scenario is without speech and noise levels defined, SNR Not Defined:

Speech/Noise Not Defined

Without sound levels defined, the resulting STI values are purely a measure of the impulse response. U50 and U80 are not shown, as without an SNR, these parameters will equal C50 and C80, respectively.

Expanding ADVANCED displays the modulation transfer indices (MTI) and modulation transfer function matrix (MTF Matrix). The COPY VALUES button will copy this data with full precision to the clipboard for pasting into spreadsheet software.

STI Advanced

Speech/Noise Scenario

Click ADD SCENARIO to add a speech/noise scenario.

Speech/Noise Scenario

  • The scenario name can be edited directly.

  • Speech and background noise values at the receiver position must be entered manually in octave bands (125 Hz to 8 kHz).


    In general, these values must be determined outside of IRIS. See STI Applications for details.

    A preset list of speech efforts and background noise are included. Please read Preset Sound Levels before using them.

  • The A (A-weighting), NC (Noise Criterion) and NR (Noise Rating) fields will update according to the octave band data.

  • The +1 or -1 buttons shift the respective octave band values up or down by 1 dB.

  • All fields must be completed for the STI and U results to be displayed, and the speech and noise data to be saved.

  • The circular + or - buttons duplicate or remove the scenario.

  • Check ON OFFICE PATH to include that scenario in the open plan office calculation. Only one scenario per measurement can be included.


    A full spectrum of tab-separated-values can be pasted into a speech/noise scenario by placing the cursor in the 125 Hz field and selecting paste.