FONIX® 8000 - Frye Electronics

Chapter 7 145
The ISTS Test
The ISTS Test screen performs coupler measurements to the upcoming IEC
60118-15 standard titled, “Electroacoustics – Hearing Aids – Part 15: Methods
for characterizing signal processing in hearing aids with a speech-like signal.”
The ISTS is part of a new way of performing coupler measurements on
advanced digital hearing aids, representing a major departure from the traditional
ANSI method of evaluating hearing aid performance.
The acronym ISTS actually refers to the speech-like signal that is used as part of
the test. It standards for “International Speech Test Signal,” and was developed
by the European Hearing Instrument Manufacturers Association which holds
the copyright. This signal was developed from recordings of female speakers of
Arabic, English, French, German, Mandarin and Spanish. The recordings were
cut into short segments and recomposed in random order.
During the test, third octave analysis is performed on the hearing aid response
to the ISTS signal for a choice of 10, 20 or 45 seconds (actual test times are
slightly longer). When the test is complete, the results are displayed as the longterm
speech spectrum (LTASS), and the 30%, 65% and 99% of the distribution
of sound pressure level.
See Figure 7.0 for a screenshot of a completed ISTS Test. Notice that the results
are shown as a series of connected horizontal segments. These segments represent
the third octave intervals used for the measurements. That is, each segment
shows the frequency response across the entire third octave interval. In all other
respects, however, they can be interpreted similarly to any hearing aid frequency
response curve.