Abstract
The quality of low bit-rate coding algorithms standardized under ISO/MPEG has been carefully verified by subjective listening tests using audio material of the highest technical quality. When using digital audio compression in the context of television sound systems, however, the question arises, as to how the coders would perform with imperfect audio signals, such as those obtained from impaired film material. This paper describes studies into the effects of the more severe impairments present in film soundtracks upon MPEG-I Layer-2 and Layer-3 audio coding, which have been carried out within the European RACE `COUGAR' project programme R2122.

Abstract
Perceptual audio coders rely on the efficient reduction of perceptually irrelevant components of the audio signal as well as on the removal of statistical signal redundancies to achieve good coding gains. In order to reach high compression ratios without reducing the subjective quality of the encoded audio signal, it is necessary to identify critically interdependent functional units of the encoding algorithm and to jointly optimize their performance. A flexible and interactive simulation and analysis environment has been programmed to assist the development and optimization of a new perceptual audio coder. The main features of this environment will be explained and the most relevant aspects that were found to limit the encoding performance will be presented.

Abstract
ATM networks will support new multimedia services that will require new protocols. Those services and protocols will need different test strategies and tools. In this paper, the concepts of functional and non-functional testers of ATM networks are discussed, a multimedia service and its requirements are presented and, finally, a summary description of an ATM network and of the test tool that will be used to validate it are presented.

Abstract
This paper presents a Multimedia Art Directory, that has been developed for an ATM network, by describing its main characteristics and the creation environment and the network facilities used.

Abstract
The cross-correlation between i(DD) and v(out) signals is addressed as a means for improving the testing of analogue circuits. Besides the higher testing confidence provided by mixed i(DD)/v(out) monitoring, a single unified test operation is performed instead of two separate operations.

Abstract
A theory based on the Kukhtarev-Vinetskii model is developed that provides the evolution equation of one-dimensional optical spatial solitons in photorefractive media. In the steady-state regime and under appropriate external bias conditions, our analysis indicates that the underlying wave equation can exhibit bright and dark as well as gray spatial soliton states. The characteristics of these self-trapped optical beams are discussed in detail. (C) 1995 Optical Society of America