Question 9/XII - Sidetone
(continuation of Question 9/XII studied in 1984-88; new wording)

Considering

(a) that from the point of view of the talker in quiet surroundings a
sidetone rating method STMR (Sidetone Masking Rating - Recommendations
P.76, P.79) that treats the human sidetone as a masking threshold yields
results that correlate well with the subjective effects of sidetone;

(b) that from the point of view of the subscriber considered as a
listener in noisy conditions the STMR method can, if associated with the
sidetone sensitivity measured with room noise, be used to derive a
listener sidetone rating (LSTR) that correlates well with subjective
effects of listener sidetone;

(c) that for various connection conditions values for STMR and LSTR are
recommended in G.121 and P.11;

(d) that digital exchanges or systems can present an unfavourable
impedance to the telephone set and increase sidetone levels and short
delay echo signals on some connections;

(e) that in order to achieve adequately high values of LSTR under
adverse connection and/or room noise conditions some manufacturers and
administrations will make use of noise cancelling microphones requiring
positional discipline in their use,

1. Are the values of STMR and LSTR recommended in P.11 and G.121
sufficiently comprehensive for the control of sidetone under variety of
connection conditions or does the information need to be supplemented?

2. What design criteria can be recommended to ensure that satisfactory
sidetone and/or short delay talker echo levels are maintained during
telephone conversations?

3. In what circumstances or under what conditions is it possible to
recommend the use of noise cancelling microphones, special acoustic or
electronic techniques in telephone handsets?
ANNEX

(to Question 9/XII)

Reply to Question 9/XII, section B.3.3 in Report COM XII-R 27, February
1988