Publication IEICE TRANSACTIONS (1976-1990)Vol.E69No.12pp.1303-1309 Publication Date: 1986/12/25 Online ISSN: DOI: Print ISSN: 0000-0000 Type of Manuscript: PAPER Category: Acoustics Keyword:
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Summary: A transmission performance design method for digital telephone sets is described, considering talker echo resulting from reflection at the four-wire to two-wire hybrid point in mixed digital-analogue networks. The method provides for complete international telephone connection, talker echo suppression and improved speech quality. To develop a design method with these features, first, the effect of talker echo on speech quality is evaluated. Next, digital telephone set loudness ratings are regulated as follows: 8.3 dB sending loudness rating 10 dB, 0.5 dB receiving loudness rating 4 dB. As a result, the Mean Opinion Score (MOS) for digital telephone sets in the ISDN is from 2.3 to 2.7 according to tests, considered acceptable for about 90% of subscribers.