Speech Intelligibility STI

XL2 STIPA Analyzer

Public Address (PA) systems in buildings like airports, railway stations, shopping centers, stadiums, or concert halls have to clearly inform persons in danger about escape information and directions in case of an emergency. People need to be given clear instructions so they can react quickly and in an orderly fashion – a Life Safety Code requirement.

Using a hand-held instrument, it is possible to commission the entire building by measuring just how intelligible the PA announcements will be when comprehensibility is most needed.

At a glance

  • Compliant with EN 54-24, IEC 60268-16, IEC 50849, NFPA-72
  • Ambient noise correction
  • Standardized reporting


Speech intelligibility is measured by playing a known signal (the STIPA test signal) through the PA and measuring the quality of that signal as it reaches each of the measurement positions. Factors that influence the intelligibility of speech are the signal-to-noise ratio (quality of the system), sound pressure level (loud enough but not too loud), ambient noise level (crowds or passing traffic), reverberation time RT60 (sound reflects off smooth surfaces; we need some reflections but not too many) and psychoacoustic masking effects (the announcement is masked by another louder sound).

4 Steps to Speech Intelligibility Measurement

  1. 1.
    Record the background noise with an XL2 when the location is full.
    XL2 STIPA background measurement
  2. 2.
    With the location empty (perhaps at night), place a TalkBox in front of the announcer’s microphone.
    TalkBox with announcement microphone
  3. 3.
    Press Start button on the XL2 to measure the STI.
    XL2 STIPA measurement
  4. 4.
    Print your Report.
    STIPA Report with your logo

Download Quick Guide to STI Measurement

Learn more about Speech Intelligibility Measurements

This webinar explains the measurement methods, workflow and result reporting for Speech Transmission Index for Public Address (STIPA) according to the latest standard IEC60268-16, edition 2011.

STI Measurement with XL2 Analyzer

The XL2 Analyzer, with the STIPA Option installed, measures the speech intelligibility according to the latest revision of standard IEC 60268-16:2011 (edition 4) and older editions. It offers ambient noise correction and automated averaging for repeated measurements. The XL2 displays the speech transmission index (STI) and the common intelligibility scale (CIS), accompanied by the individual levels and modulation indices of the seven octave bands. All data is stored automatically with a location ID for standardized documentation using the NTi Audio STI Reporting Tool.

XL2 STIPA Analyzer


  • Standards: IEC60268-16 (edition 2, 3 and 4), ISO 7240-16, ISO 7240-19, DIN VDE 0828-1, DIN VDE 0833-4
  • Ambient Noise Correction
  • Automated Averaging
  • Display of Modulation Indices

STI Reporting Tool

STIPA Reporting Tool

The STI Reporting Tool creates measurement reports according to the IEC 60268-16 and VDE0833 standards. The tool calculates the effect of the actual ambient noise caused by the public onto the measured speech intelligibility. Thus it provides you the expected speech intelligibility in STI or CIS during real-life emergency announcements.

System Requirements:
  • PC running Windows XP, 7, 8 and 10
  • Excel 2010, 2013 or 2016 (32 bit or 64 bit)

Download here

Test Signal Source

NTi Audio TalkBox

The NTi Audio TalkBox is required for the verification of installations where voice microphones are in use. The TalkBox produces a calibrated, acoustic, speech-intelligibility test signal that is picked up by the operator’s microphone. The TalkBox simulates a human talker in accordance with the IEC 60268-16 standard, thereby including the microphone and the acoustic environment of the operator’s location in the test. The entire signal path is thus tested, providing a complete STIPA speech intelligibility measurement.

The TalkBox provides two major advantages for STIPA measurements:
  • An extended test coverage and an easy to handle test signal injection.
  • Sampling frequency deviations - a dangerous trap when using portable CD players - are completely eliminated.


Minirator MR-PRO

Minirator MR-PRO

The Minirator MR-PRO is used for electrical signal injection into public address systems that commonly use alarm messages from a hard drive (systems without a microphone).


STIPA Test Signal CD

This CD is included with STIPA Option Package.

XL2 Kit for Speech Intelligibility Measurements

Exel Set for STI-PA Testing
  • XL2 Audio and Acoustic Analyzer
  • STIPA Option for XL2
  • M4261 Measurement Microphone
  • Minirator MR-PRO
  • ASD Cable for XL2
  • Cable Test Plug (MR-PRO)
  • 2x Mains Power Adapter
  • 3x Calibration Certificates
  • Exel System Case
  • TalkBox

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