Professional Audio & Video Solutions

Audio Precision Adds STI (STIPA) Measurement Capability to APx500 Software

Audio Precision Adds STI (STIPA) Measurement Capability to APx500 Software

Quantifying the Intelligibility of Speech

Developed as a method for quantifying the intelligibility of speech with respect to a transmission medium—for example a room, an intercom system, a radio link—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).

    Quantifying the Intelligibility of Speech

  • 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. Using this signal, a single measurement is made, with total measurement time taking ~10-20 seconds. The STIPA method shows excellent correlation with the “Full STI,” the most comprehensive measurement method covered by the standard. In contrast to STIPA’s measurement time of about 15 seconds, the Full STI takes over 15 minutes to complete.

  • Integrated Audio, Electro-Acoustic and STI Measurement

  • Using the APx STI measurement enables developers to verify the STI performance of their designs with AP’s industry-leading instrumentation, and use that same test equipment for the rest of their audio and electro-acoustic test requirements. Once the plug-in is installed, the STIPA measurement can be easily incorporated into any measurement sequence. Additionally, the plug-in includes a Speech Level measurement that conforms to Annex J of IEC 60268-16, for proper adjustment of the STIPA signal level.

  • Main Advantages

    Fast measurement
  • An standard
  • extra quality info about your DUT
  • Intergrated in APx Software
  • Easy reporting

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Related Blog messages

  • What is new in APx software 4-4

    The latest release of APx500 audio measurement software, version 4.4, is available for download at

    The release includes minor feature improvements, including regulation enhancements and the option to maintain Bluetooth® connection even when Bluetooth is not selected as output or input.

    APx500 Measurement Software
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  • Perceptual audio analyse met APx 525


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    Pulse Density Modulation (PDM) is a one-bit, high rate data stream that conveys a signal by modulating the density of the pulses. A typical application for PDM is the Micro-Electrical-Mechanical System (MEMS) microphone found on smartphones.

    The APx PDM option provides direct connectivity for audio devices that have a PDM output (such as a MEMS microphone) or input (such as the decimator on a smartphone chip). In addition to all the standard audio measurements, APx provides variable DC voltage, variable sample rate, and a PSR (power supply rejection) measurement to test the device’s full operating parameters. No other analyzer combines direct PDM connectivity with APx’s best in class speed, ease-of-use, and performance.