1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 . TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU-!).4%.!.#%G0G0/10 kHz;5, 6.4 and 7 kHz.From the point of view of sound-programme transmission ordinary telephone circuits are generally consideredto be suitable only for the transmission of speech. It should
2、 be noted that the limits of the loss/frequency distortioncannot be guaranteed to be better than the limits shown in Recommendation M.580 4.When a telephone circuit is used for a sound-programme transmission the terminating sets and the signallingequipment must be disconnected to avoid echo effects
3、and false operation of the signal receiver.When a telephone circuit is used for a sound-programme transmission, a point of zero relative level of thetelephone circuit must coincide with a point of zero relative level on the sound-programme circuit. (However, see 2 ofRecommendation N.15 in which it i
4、s pointed out that a 6-dB loss should be introduced in order to reduce the meanpower level delivered to the telephone circuit system).References1 CCITT Recommendation Performance characteristics of 15 kHz type sound-programme circuits, Vol. III,Rec. J.21.2 CCITT Recommendation Performance characteri
5、stics of 10 kHz type sound-programme circuits, Red Book,Vol. III, Rec. J.22, ITU, Geneva, 1984.3 CCITT Recommendation Performance characteristics of narrow-bandwidth sound-programme circuits,Vol. III, Rec. J.23.4 CCITT Recommendation Setting up and lining up an international circuit for public telephony, Vol. IV,Rec. M.580._1)This Recommendation applies also to 7 kHz and 15 kHz digital sound-programme circuits.
