Modulated noise reference unit (MNRU) tests using DRT, DAM, and spelling alphabet test materials
Astrid Schmidt-Nielsen, Retha A. Sueda, Thomas E. Tremain, William D. Voiers · The Journal of the Acoustical Society of America · 1990
The modulated noise reference unit (MNRU) has been widely used for reference conditions in evaluating voice coders for telephone applications. Opinion scores using the mean opinion score (MOS) are referenced to equivalent modulated signal-to-noise level. The DoD Digital Voice Processor Consortium has conducted extensive tests of voice processors using the Diagnostic Rhyme Test (DRT) to evaluate intelligibility and the Diagnostic Acceptability Measure (DAM) to evaluate acceptability. Spoken materials for the DRT, the DAM, and the ICAO spelling alphabet words and digits were degraded by speech-modulated noise at levels from + 30 to − 15 dB. The resulting tapes were evaluated by trained listeners. Even small amounts of noise degraded acceptability, DRT intelligibility degraded more slowly, and the spelling alphabet was moderately intelligible even at the worst speech to noise levels. Relations among the different types of tests will be discussed.