NTi Audio Acoustilyzer AL1 - Manual (Page 60)

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f. STI-PA Measurement Hints
1. Any background noise has to be sufficiently static during the
measurement, e.g. pink noise fulfills this requirement.
2. Verify the environmental conditions prior to testing. Run STI-PA
measurements without any test signal - the results should be < 0.20
STI.
3. Impulsive background noise during the measurement, such as speech,
causes severe measurement errors. The STI-PA result is usually too
high.
4. In case such impulsive noise can not be prevented, the measurements
might be shifted e.g. to night time, and afterwards corrected with the
averaged daily background noise, using external post processing.
5. Any CD-Player used to reproduce the STI-PA test signal has to be
accurate, as only limited time-shifts (+/- 200 ppm) are allowed to
ensure reliable STI-PA test results. Pitch control and shock protection
should be disabled. NTi Audio recommends the use of professional CD-
players only. You may verify the time shift of your CD-Player with a 9
kHz test signal:
•
Generate a 9000 Hz sine signal using the NTi Audio Wavefilegenerator
(available for download at the NTi Audio-website -> Acoustilyzer) and
copy this on a CD
• Insert this CD into the CD player and play the 9 kHz test signal
• Connect the Acoustilyzer directly to the CD-player audio output and
measure the signal frequency in the RMS/THD mode. The displayed
frequency should be in the range from 8998 to 9002 Hz (the last digit
difference represents 111 ppm at 9 kHz)
6. The STI-PA test signals of other test system manufacturers may sound
similar but are not compatible. Only the NTi Audio STI-PA test signal
CD V1.1 or higher should be used in combination with the Acoustilyzer
AL1.
7. STI-PA measurement of alarm systems should be carried out in simulated
emergency conditions (same sound pressure level and all components
activated).
8. At locations with variable conditions, e.g. public areas with few people or
crowded areas, the worst-case STI-PA results have to be measured.