On one basic rate ISDN access, two B-channels are offered with a capacity of 64 Kbits/s per channel. Using two basic rate access, ITIS has demonstrated that it is possible to transmit CD quality stereo sound through the ISDN, with a bandwidth of 20-20 000 Hz. To transmit a true stereo sound without any random delay between right and left channels, four B-channels are established between the transmitter and the receiver, providing a 4 x 64 Kbits/s capacity. These four channels are then associated and synchronized (the ISDN does not guarantee equal transmission delays for the different channels) in order to obtain a fully transparent channel at 256 Kbits/s. Left and right audio signals are encoded at 128 Kbits/s each, with Musicam coding algorithm (standard ISO CN n° 11172-3 Layer II), and multiplexed on the 256 Kbits/s channel. Thanks to the dedicated synchronization method, sound is transmitted without perceptible delay (live applications are possible) and without stereophonic alteration. Set up time is only five seconds. Applications of this new technique are temporary links between reporting site, concert hall and studios, and also automatic backup of leased lines between studios, or studios and radio transmitters, etc. Prototype equipments (transmitter and receiver) have been developed by ITIS. Operational tests have confirmed the qualities of the technique.
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