Methods for Subjective Determination of Transmission Quality - Series P: Telephone Transmission Quality; Methods for Objective and Subjective Assessment of Quality
|Publication Date:||1 August 1996|
This Recommendation contains advice to Administrations on conducting subjective tests of transmission quality in their own laboratories. It does not however deal with types of tests described in detail in other ITU-T Recommendations and documentation, namely:
a) determination of Reference and Relative Equivalents - see Handbook on Telephonometry, Geneva, 1993;
b) determination of Loudness Ratings - see Recommendation P.78;
c) determination of Articulation Ratings (A.E.N. values) - see Handbook on Telephonometry, Geneva, 1993.
Neither does it deal with the various kinds of specialized tests used in the course of developing items of telephone equipment, for the purpose of diagnosing faults and shortcomings, such as Diagnostic Rhyme Tests  and other tests dedicated to the study of specific aspects of speech output.
This Recommendation gives the approved methods which are considered to be suitable for determining how satisfactorily given telephone connections may be expected to perform.
The methods indicated here are intended to be generally applicable whatever the form of degradation factors present. Examples of degrading factors include: loss (often frequency dependent); circuit noise; transmission errors (random bit errors as well as erased frames that occur in systems such as mobile communications); environmental noise; sidetone; talker echo; non-linear distortion of various kinds including low bit-rate encoding; propagation time; harmful effects of voice-operated devices; distortions of the time scale arising from packet switching; and time-varying degradations of the communication channel, including those arising in loudspeaking sets. Combinations of two or more of such factors also have to be catered for. Further guidance for specific applications is available in Recommendations P.830 (digital speech codecs), P.84 (DCMEPCME), and P.85 (speech output devices).