The Modulated Noise Reference Unit (MNRU) is a standalone unit that is intended to introduce controlled degradations to speech signals. Various organizations (Administrations, scientific/industrial organizations), as well as the ITU-T itself, have made extensive use of the MNRU concept for evaluating the subjective performance of digital processes (in arriving at Recommendations G.722 and the 32 kbit/s ADPCM algorithm of Recommendation G.726, for example). A modified version for use in evaluating codecs of wider bandwidth (70-7000 Hz) is now common practice. However, the actual devices used, while based on common principles, may have differed in detail, and hence the subjective results obtained may also have differed. (Differences in subjective testing methodology are also relevant.) The purpose of this Recommendation is to define the narrow-band and wideband versions of the MNRU as completely and in as much detail as possible in order to minimize the effects of the device, and of its objective calibration procedures, on the results of subjective tests.
ITU-T P.810 FRENCH-1996 Referenced Document
ITU-T G.191-1993 Software Tools for Speech and Audio Coding Standardization (Study group 15)
ITU-T P.56-1993 Objective Measurement of Active Speech Level - Telephone Transmission Quality Objective Measuring Apparatus (Study Group XII) 15 pp
ITU-T P.80-1993 (WITHDRAWN) Methods for Subjective Determination of Transmission Quality - Telephone Transmission Quality - Subjective Opinion Tests Study Group XII; 24 pp; Cancelled
ITU-T P.830-1996 Subjective Performance Assessment of Telephone- Band and Wideband Digital Codecs - Telephone Transmission Quality Methods for Objective and Subjective Assessment of Quality (Study Group 12) 27 pp