3M C860, Руководство пользователя

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3M
Commercial Care Division
Food Service Business
3M Center
St.
Paul, MN 55144-1000 ©3M 2005 20050718
Wireless Intercom Systems
Technical Bulletin July 18, 2005
Speech Intelligibility and Sound Quality
Competitive Comparison
3M Commercial Care Division contracted with Orfield Laboratories, Inc.¹, a sound testing company, to
independently compare the audio of the 3M™ Wireless Intercom, C1060 analog intercom system to a
competitive digital intercom system. Testing focused on inbound intercom intelligibility performance,
specifically in the presence of a uniform background noise field at the menu post.
For the tests, Speech Transmission Index (STI) was calculated in accordance with International
Electrotechnical Commission (IEC) 60268-16; Objective rating of speech intelligibility by speech
transmission index. System frequency response was also measured.
For speech intelligibility testing, a broadband noise signal (pink noise) was used at the menu order post to
provide various background noise conditions. This noise was used to simulate typical environmental
sound levels found in real intercom installations. For all tests, system inbound and outbound levels were
calibrated to provide identical levels (dBA). Background noise levels were also calibrated and monitored.
The relationship between reported STI scores and “subjective evaluation” can be described as shown in
Table 1.
STI “Subjective Evaluation”
0.0 – 0.3 Bad
0.31 – 0.45 Poor
0.46 – 0.60 Fair
0.61 – 0.75 Good
0.76 – 1.00
Excellent
Table 1: STI Score vs. “Subjective Evaluation”