Svantek SV 977D User Manual

113
SV 977D User Manual
13 MEASUREMENT OF SPEECH TRANSMISSION INDEX – STIPA
13.1 INTRODUCTION
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 SV 977D in accordance with IEC 60268-16:2011.
Note: In addition to the fact that measurements can be made using only SV 977D, Svantek also
provides an application (BA Assistant) for mobile devices (smartphone, tablet) with Android 7.0
platform or higher, which performs STIPA measurements using SV 977D but has a more convenient
user interface (see BA Assistant User Manual).
13.2 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
.
13.3 SELECTING 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!

Svantek SV 977D Specifications

General

Brand	Svantek
Model	SV 977D
Category	Measuring Instruments
Language	English