The ITU Radiocommunication Assembly considering a) that digital audiovisual and audio services have rapidly developed in the last few years, based on advances in digital signal compression and communication technologies; b) that the digital services are characterized by a multiplicity of signals and especially audio signals; c) that distribution and broadcasting networks for digital services and specially audio services are composed of a multiplicity of cascaded links such as satellites, terrestrial radio links, computer networks and wireless broadcasting or cable distribution to the end-user; d) that the whole delivery chain is composed of a multiplicity of cascaded processing systems such as converters, encoders, switches, multiplexers, modulators, receivers, etc.; e) that analogue and digital disturbances or errors on the delivery chain introduce different types of impairments on audio signals; f) that some of these disturbances are inaudible because of error concealment strategies built into the network and do not influence the perceived audio quality; g) that state-of-the-art troubleshooting systems are adequate to detect long duration impairments on audio sequences, but have limited efficiency for in-service detection of short breaks which are more frequent on digital services; h) that Recommendation ITU-R BS.1387 offers ways to evaluate the perceived audio quality of mono and stereo signals in the presence of a full-bandwidth unimpaired reference signal; j) that in-service monitoring in general has no access to the full-bandwidth unimpaired reference signal; k) that for some channels a low bit-rate side channel is available to be used for service quality monitoring; l) that in-service monitoring has the requirements of low computational complexity and simple user interfaces; m) that different proprietary solutions are proposed but needs for a common standard have been expressed; n) that commercial contracts impose that network operators must keep the perceived audio quality of the delivered services within agreed limits; o) that quality evaluation in general has been recognized both by ITU-R and ITU-T and they both have set up Questions on studies related to this topic; p) that none of these Questions is related to in-service quality monitoring of perceived audio quality