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127
SVAN 979 User Manual
14
STI CALCULATIONS
– STIPA
14.1 I
NTRODUCTION
The Speech Transmission Index (STI) is applied in the deterioration of the speech intelligibility induced by the
transmission channel. The STI method involves the use of a test signal applied to the transmission channel, and an
analysis of the received test signal. The speech transmission quality of the channel is determined and expressed in
values from 0 to 1 in the form of STI. Using the obtained STI value, it is possible to determine the potential speech
intelligibility.
The applications of STI include evaluation of sound reinforcement and emergency systems, communication channels,
speech intelligibility, communication in rooms and auditoria, etc.
STIPA (
speech transmission index for public address systems)
is a STI derivative approach that was developed
for fast measurements of electro-acoustic and acoustic environments effects that affect the speech intelligibility
in the room acoustics and/or public address systems
.
STIPA calculations are realized in SVAN 977A in accordance with IEC 60268-16:2011.
Note: In addition to the fact that measurements can be made using only SVAN 979, Svantek also
provides an application (BA Assistant) for mobile devices (smartphone, tablet) with Android 7.0
platform or higher, which performs STIPA measurements using SVAN 979 but has a more convenient
user interface (see BA Assistant User Manual).
14.2 STI
METHOD BACKGROUND
The STI method is based on measurements of the STI test signal comprising seven octave band noise signals
corresponding with the octave bands from 125 Hz up to 8 kHz. Each noise carrier is modulated with one or more
modulation frequencies at one-third octave intervals ranging from 0,63 Hz up to and including 12,5 Hz. Such test
signal which simulates speech fluctuations is reproduced in a room or through a communication channel and
received at a listener position (superimposed by distortions presented in the room like echoes or noise) by means
of omnidirectional microphone.
The STI method determines the modulation transfer function
m
(
F
)
– reduction in the modulation depth for modulation
frequency - of the transmission channel for the seven octave bands. The RMS level of each octave-band carrier
matches the relative level of the average, long term spectrum of speech material. Each octave band has a
contribution to speech intelligibility which is weighted according to that band. Using the weighted sum of these
transmission index values, the overall STI value for the transmission channel is determined.
STIPA method uses two modulation frequencies per octave band that
are generated simultaneously giving a
total of 14 modulation indices
.
14.3 S
ELECTING THE
STIPA
FUNCTION
To activate the
STIPA
function, select the
STIPA
position in
the
Measurement
Function
list and press
<ENTER>
.
<ENT>
Note: The STIPA function is optional and should be unlocked by entering the activation code in the
text editor screen, which is opened after first attempt to select this function. Once unlocked this option
will be ready to use permanently.
Note: It is not possible to change the current function during running measurements.
In this case the instrument displays for about 2
seconds the warning: “Measurement in Progress”. To
change the current measurement function, the measurement must be stopped!
Summary of Contents for SVAN 979
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Page 275: ...275 SVAN 979 User Manual Appendixes 7100 Hz 8000 Hz 8500 Hz 9000 Hz 9500 Hz 10000 Hz ...
Page 312: ...312 SVAN 979 User Manual Appendixes Summary curve ...
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Page 370: ...370 SVAN 979 User Manual Appendixes O ring gasket locations inside ...