Question 8/XII - Improvement of the methods for the determination of
loudness ratings
(New Question)

Considering

(a) that the methodology for the determination of loudness ratings has
been defined in a number of CCITT P-Recommendations;

(b) that following the world-wide use of loudness ratings it seems that
some of the methods are not perfect so far as the accuracy,
reproducibility, comparability and simplicity are concerned;

(c) that there is widespread usage of headsets in telephony;
(d) that there have been recent advances in both headset technology and
complexity;

(e) that the results of subjective and objective measurements on
headsets have been studied in the last Plenary period but further
analysis is required;

(f) that the IEC-711 occluded ear simulator has been adopted within
Recommendation P.51 for ear insert receivers, but other types of headset
receivers do not have recommended test methods.

PART A - HANDSETS

The following Questions should be studied:

a) What improvement should be made to Recommendation P.78 for the
determination of loudness ratings for special purposes?

Note 1 - Although the network planning mainly depends on the objective
measured data of loudness ratings, however, subjective determination
will still be necessary in some cases, for example, the determination of
SLRs of certain types of carbon sets, or a new design of telephone set
with non-linear amplitude characteristics.

Note 2 - A method using the direct balance technique against IRS for the
subjective determination of loudness ratings is described in Supplement
No. 17 Volume V of the Blue Book.

b) What improvement should be made to Recommendations P.64 and P.75 for
the determination of sensitivity/frequency characteristics of a local
telephone system including telephones using non-linear techniques and/or
noise cancelling microphones.

Note 3 - Annex 1 summarizes the progress of the study of the previous
Question 8/XII (measuring the efficiency of a microphone or a receiver),
especially for the carbon microphones.

Note 4 - Study of the difference between SMJ and SmJ, i.e., the sending
SFC measured by real mouth and by artificial mouth, LM, and the earphone
coupling loss, LE are covered by the present Question.

Note 5 - The artificial mouth and the artificial ear used for the
determination of sensitivity/frequency characteristics are studied under
Question 12/XII, and the algorithm used for the calculation of loudness
ratings is studied under Question 15/XII.

c) What improvement should be made to Recommendation P.65 on the
instrumentation for the objective measurement of loudness ratings?

Note 6 - Description of some existing instruments for the objective
measurement of loudness losses (including LR, R25E etc.) is given in
section 5 of the Handbook on Telephonometry.

Note 7 - During the study period 1985-1988 modifications have been made
to some types of the instruments mentioned above. These points can be
found in a number of contributions of the study period.

PART B - HEADSETS

What precautions should be recommended when measuring the performance of
special types of headsets?

Examples of special types of headsets:

i) headsets with noise cancelling microphones;

ii) headsets with intra-concha, circumaural and non-contact types of
receivers;
iii) headsets with either dual receivers or "dual receive-path"
receivers.
ANNEX 1

(to Question 8/XII)

Reply to Question 8/XII in Report COM XII-R 27, February 1988,
sections B.2.2.2 and B.2.2.3