NTi Audio
XL2 Speech Intelligibility Analyzer

Speech Intelligibility STI

Public Address (PA) systems in buildings like airports, railway stations, shopping centers or concert halls have to clearly inform persons in danger about escape information and directions in case of an emergency. Using a hand-held instrument, it is possible to determine the intelligibility of the messages spoken through the PA by measuring at all public points within the building. This is achieved 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. The XL2 Analyzer measures the speech intelligibility of emergency announcement systems in accordance with the IEC 60268-16:2011 standard (edition V4.0).

Factors that influence the intelligibility of speech are the signal-to-noise ratio and frequency (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).

Technically speaking, the XL2 measures and calculates the speech transmission index (STI) and the common intelligibility scale (CIS), accompanied by the individual levels and modulation indices of the seven octave bands. The sound source is the dedicated STIPA test signal. The STI is reliably measured within 15 seconds at each position.

STI Measurement with XL2 Analyzer

An 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 includes ambient noise correction and automated averaging of measurements. The XL2 displays the measurement results as STI or as CIS results, accompanied by the individual levels and modulation indices of the seven octave bands.

The measurement results are acquired from the dedicated STIPA test signal source:
  • NTi Audio TalkBox
    Acoustic signal generator, required for audio systems with voice microphones, thus measuring the complete signal chain.
  • Minirator MR-PRO
    Test signal generator, required for audio systems with line inputs
  • STIPA Test CD

NTi Audio #: 600 000 338

XL2 STIPA Analyzer

STI Reporting Tool

STIPA Reporting Tool(Click to enlarge)

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.

The STI Reporting Tool is free to download at the XL2 Support website.

System Requirements:
  • PC running Windows XP, Vista or Windows 7
  • Excel 2003, 2007 or 2010 (32 bit or 64 bit)

Webinar on Demand

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.

(recorded on 27 February 2013)

Useful Links from this Webinar

Test Signal Source

NTi Audio Talkbox

NTi Audio TalkBox

The NTi Audio TalkBox is required for audio systems with voice microphones.

The NTi Audio TalkBox feeds the test signal into the operator microphone of sound reinforcement systems. It presents the standardized voice-like acoustic signal emission simulating a human talker according to IEC 60268-16, combined with a TNO certified speech intelligibility signal at standardized levels. This setup considers the entire signal path for an accurate STIPA measurement. It includes all effects of the operator's microphone and environment.

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.

Order Information

Exel Set for STI-PA Testing

Exel Kit for Speech Intelligibility Measurements

  • XL2 Audio and Acoustic Analyzer
  • STIPA Option for XL2
  • M4260 Measurement Microphone
  • Minirator MR-PRO
  • ASD Cable for XL2
  • Cable Test Plug (MR-PRO)
  • 2x Mains Power Adapter
  • 3x Calibration Certificates
  • Exel System Case

NTi Audio TalkBox

NTi Audio #: 600 000 085

Get more Information

Buy at the web shop or contact NTI Americas .

Contact NTi Audio

NTI Americas Inc.
Tigard, Oregon
Thomas E. Mintner
+1 503 684 7050

Links to Solutions


Application Notes