NTIA Releases Digital Audio Report
Tuesday, June 10, 2008 | Comments

  




By Sandra Wendelken

The National Telecommunications and Information Administration (NTIA) released a report outlining testing to determine how high-noise firefighting scenarios affect digital and analog networks’ audio quality. The tests, conducted for the International Association of Fire Chiefs (IAFC), include comparisons of three primary communications systems — a 25-kilohertz analog FM radio pair, baseline Project 25 (P25) full-rate IMBE vocoder radio pair and enhanced P25 full-rate IMBE vocoder radio pair — in nine different noise environments.

“The performance of the 25-kilohertz analog system was either statistically similar to or better than the P25 systems for all environments,” the report said. “Four of the nine environments were too difficult for intelligible communication using all tested systems (i.e., less than 10-percent intelligibility).”

This test also evaluated a 12.5-kilohertz analog FM radio pair on three of the nine environmental noise conditions. The inclusion of this radio pair was to evaluate the intelligibility of a communications system that meets the upcoming FCC mandate requiring narrowband devices. “The 12.5-kilohertz analog system was statistically similar to the 25-kilohertz analog system,” the research said.

In the case of voice transmissions while using a mask, there was a significant degradation in intelligibility for the P25 vocoders, according to the report. The Personal Alert Safety System (PASS) alarm, designed to augment safety of first responders, significantly degraded intelligibility of both P25 vocoders. The low air alarm was effectively too difficult a noise environment for all of the tested communications systems. However, the 25-kilohertz analog system and the P25 enhanced full-rate system preserved the noise characteristics of the low air alarm sufficiently well that a listener could determine what type of alarm was sounding.

“While this information may be useful to those planning to purchase and deploy new radio systems for their agencies, these results should not be the sole source of information,” the report said, noting current assets, operating procedures, policies, budget plans, spectrum availability and state communications interoperability plans (SCIPs) should be considered as well.

Audio files from the report, funded by the National Institute of Standards and Technology (NIST) and Department of Homeland Security (DHS) and authored by Institute for Telecommunication Services (ITS) employees D.J. Atkinson and Andrew A. Catellier, are available at the links below.

Analog Radio Sample Audio

Project 25 Baseline Vocoder Sample Audio

Project 25 Enhanced Vocoder Audio

The full report can be accessed here.

IAFC posted a document with portable radio best practices on its Web site for its members. “The majority of these practices are suggestions that radio users can be trained to consider when using a portable radio in a high-noise environment,” the document said. “Some of the suggested practices are technical or procedural considerations that organizations should consider adopting to maximize user safety and efficiency.”

The IAFC best practices document is available on its Web site.

Access background on the digital noise testing.

See the results of a MissionCritical Communications reader survey about digital technology used by firefighters.


Sandra Wendelken is editor of MissionCritical Communications. E-mail comments to swendelken@RRMediaGroup.com.



 
 
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