Audio Precision introduces new STI measurement solution for Speech Transmission Index

Beaverton, OR, October 30, 2015: Audio Precision, the authority on audio testing, today announced the addition of the Speech Transfer Index (STI) plug-in to its APx500 audio testing software. The Apx500 STI plug-in is designed for development engineers of public safety (police, fire, emergency) communications, public address systems, flight recording equipment, with measurement capabilities in compliance with the international standard IEC60268-16 (2011).

Quantify speech intelligibility

STI quantifies speech intelligibility across different transmission media (e.g. rooms, intercom systems, radio lines), can objectively rate language between 0-1, and is used to predict syllables, words transmitted in a specific medium , whether the sentence is easy to understand. Ratings range from “Poor” (0-0.36) to “Excellent” (0.75-1.0).

Of the four direct measurement methods described in IEC 60268-16 (2011), the Apx500 STI plug-in uses the most commonly used STIPA (Speech Transmission Index for Public Address) technique. STIPA uses 14 modulation frequencies in 7 octave bands, each band is modulated with two frequencies, and all bands, frequency combinations are contained in one signal. Using this signal for a single measurement, the total measurement time takes 10-20 seconds. The STIPA method is very similar to the “full STI” method, which is the most comprehensive measurement method in the standard. STIPA measurement time is about 15 seconds, while “full STI” takes about 15 minutes.

Integrate audio, electroacoustic, and STI measurements

With APx500 STI measurement software, developers can use AP’s best-in-class measurement instruments to verify the STI performance of their designs, and the same equipment can be used for other audio and electro-acoustic tests. After installing the plug-in, STIPA measurement functionality can easily be added to any measurement sequence. In addition, for proper adjustment of STIPA signal levels, the plug-in includes a voice level measurement function according to IEC 60268-16 Annex J.

“With the release of the APx500 STI plug-in, system developers now have a lab-quality tool to verify the STI performance of their designs,” said Dave Schmoldt, CEO of Audio Precision. Audio and electro-acoustic testing, including 16 input channels, a variety of digital interfaces, and a very intuitive user interface.”

Ordering Information

Users can now order the STI option with the APx500 analyzer family or order the APX-SW-STI upgrade. For the demo version of APx500 STI, please go to to download.

About Audio Precision Corporation

Audio Precision is a recognized leader in audio testing, headquartered in Beaverton, Oregon, USA. Since 1984, AP has provided high-performance audio analysis instruments and applications, helping engineers around the world design and manufacture different types of innovative consumer, professional and industrial audio and acoustic products.

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