Vox -01 Operating Manual page 12

The "measurement details" screen shows all the diagnostic details of an individual STI
measurement:
• OCT: The octave center frequency (Hz)
• REL: The octave band levels relative to the STIPA signal spectrum (this is
effectively the frequency transfer function of the tested channel in octaves).
• MTI: Modulation Transfer Index. This quantifies the contribution to the
overall STI from each octave band.
• mr: the m-values (modulation transfer function in octave band OCT for
modulation frequency mf). These m-values are uncorrected, not adjusted
for masking effects and additive noise. Since the STIPA signal features two
modulation frequencies per octave band, there are also two m-values per
octave band. The modulation frequencies are also shown (mf)
• TI: the Transmission Index per octave band for each modulation frequency
These measurement details will enable more experienced operators to determine not only
the speech intelligibility of the tested channel, but also the causes of intelligibility reduction
induced by the channel.
Settings screen (left) and additive noise screen (right)
The settings screen gives the user three options:
• Choose whether or not to display STI qualification bands (A-U) as standardized
in IEC-60268-16. These bands are used in certain applications.
• Choose to enable or disable the level dependent model features: level
dependent masking and the speech reception threshold. For standard measure
ments, these features should be turned ON. Only when all-electric transmission
chains are tested (without any acoustics involved) should these features be turned
off, since there is no acoustic level reference in those cases.
• Choose whether or not to (computationally) add noise to the measurement.
12 VOX-01 Operating Manual