Audio software tests quality of speech in radios

Audio Precision has introduced a plug-in for its APx500 audio test software to make measurements conforming to international standard IEC 60268-16 (2011).

The APx Speech Transmission Index (STI) plug-in will be used in the development of public safety (police, fire, emergency) communications and public address systems, as well as flight recorder devices.

Developed as a method for quantifying the intelligibility of speech with respect to a transmission medium, such as a radio link, the STI is an objective measure that provides a single rating between 0 and 1 that predicts the likelihood of syllables, words and sentences being comprehended within the intended medium.

The rating is broken down into qualification bands ranging from “bad” (0 to 0.36), to “excellent” (0.75 to 1.0).

Of the four direct measurement methods detailed by IEC 60268-16 (2011), the APx STI plug-in employs the most commonly used technique, STIPA (Speech Transmission Index for Public Address).

STIPA uses 14 modulation frequencies across seven octave bands, with two frequencies combined in each band, and all band-frequency combinations contained in a single signal.

The APx STI plug-in is a software option that is priced at $500.