Public Safety Audio Quality
Modified Rhyme Test
(Listen to some of the test's audio samples here.)
PURPOSE
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| Talking HATS (Head and Torso Simulator) with no mask. Radio microphone is positioned 2 inches from the LRP (lip reference point). |
The PSCR (Public Safety Communications Research) program is working with fire fighters to understand how background noise affects voice communications. The goal is to learn what technology and operational improvements may help overcome background noise issues.
METHOD
For the testing described here, the PSCR Audio Lab used a subjective intelligibility test called the MRT (Modified Rhyme Test). The test measures correct responses, rather than subjective judgment (i.e., is audio intelligibility bad, poor, good, or excellent?) as in a MOS (mean opinion score). Instead, in the MRT, listeners were asked to select from a list the word they believe they heard from the talker.
The listener was given a PDA (personal digital assistant). The listener played a randomly served sentence. After each sentence the PDA displayed a request to choose the word heard. For example:
“Please select the word _______.”
| bed | led | fed |
| red | wed | shed |
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| Talking HATS (Head and Torso Simulator) with SCBA (self-contained breathing apparatus) mask. Radio microphone is positioned 1 inch from the voice port.*
*IAFC has since changed this recommendation. It now consists of placing the microphone directly against the voice port. Future testing will follow the new recommendation. |
Fifty groups of six words were spoken by three female and three male talkers. Thirty listeners participated in the test, each of whom heard five lists of 300 sentences.
NOISE CONDITIONS
The MRT comprised nine noise conditions — either with or without an SCBA (self-contained breathing apparatus) mask with no additional noise or noise from a fire truck pump panel, a rotary saw cutting metal, a chainsaw cutting wood, a PASS (personal alert safety systems) alarm, or a low-air alarm.
For complete details about how the test was run, see NTIA (National Telecommunications and Information Administration) Technical Report TR-08-453.
Click here to listen to a few samples from the testing.
