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Audition is the most important human sensory modality in interindividual communication. Consequently, acoustics has always dealt with communication. Yet recently, due to the high amount of computing power available, communication-acoustical systems become increasingly complex and sophisticated. In particular, they become more intelligent and knowledgeable. This trend will be discussed in this chapter by taking two complementary research streams as examples which have been pursued at the Institute of Communication Acoustics at Bochum during the past three decades, namely, (a) analysis of auditory scenes with the goal of arriving at parametric representations and, complementary, (b) synthesis of auditory scenes from parametric representations. The discussion is based on two software systems which have been developed for research purposes, namely, a binaural-analysis system and an auditory-virtual-environment generator — both of which will be roughly explained. It is, however, not the aim of the chapter to introduce scientific or technological details, but rather to bring a trend to the fore which may well coin the profile of communication acoustics in the years to come.

Many organisms have evolved efficient means for acoustic communication. Adaptations can be found concerning all components of the communication system: signal generation at the sender is optimised, signal characteristics are tailored to the transmission channel, and receivers have evolved elaborate mechanisms for segregating the signals from separate sources and for analysing signal characteristics. The acoustics of the environment often imposes similar demands on the mechanisms for auditory analysis in different animal species. Thus, mechanisms of auditory analysis show many similarities in different animal species ranging from insects to mammals. These similarities result either from convergent evolution of auditory systems that are selected to achieve a similar performance or they are the consequence of the preservation of structures in evolutionary history. Examples for both types of traits are provided that have evolved as adaptations for auditory communication.

The human hearing organ is a signal processor par excellence. Its amazing abilities are often described in terms of psycho-acoustic models. However, in this chapter the focus is laid on the physical background, particularly on the physics of the peripheral hearing organ. The peripheral system can be looked at as a signal conditioner and preprocessor which stimulates the central nervous system. It comprises acoustic, mechanic, hydro-acoustic, and electric components which, in total, realize a sensitive receiver and high-resolution spectral analyzer. For daily life it is extremely important that the hearing organ can also work under adverse conditions. This includes the need for general robustness and low sensitivity with respect to varying external and internal working conditions. In the hearing organ several strategies are found which noticeably differ from technical solutions.

In many everyday listening situations, humans benefit from having two ears. For more than a century, research has been conducted to understand which acoustic cues are resolved by the auditory system to localize sounds and to separate concurrent sounds. Since Jeffress proposed the first lateralization model in 1948, binaural models have become increasingly popular to aid in understanding the auditory system and to solve engineering tasks related to the localization and detection of acoustic signals. In the following chapter, a number of binaural models will be described — starting from the classical coincidence model to recent approaches which simulate human localization in three dimensions. The equalization-cancellation model will be also addressed, as a classical example to predict binaural detection experiments.

In our natural environment, we simultaneously receive information through various sensory modalities. The properties of these stimuli are coupled by physical laws, so that, e. g., auditory and visual stimuli caused by the same event have a specific temporal, spatial and contextual relation when reaching the observer. In speech, for example, visible lip movements and audible utterances occur in close synchrony, which contributes to the improvement of speech intelligibility under adverse acoustic conditions. Research into multi-sensory perception is currently being performed in a number of different experimental and application contexts. This chapter provides an overview of the typical research areas dealing with audio—visual interaction^3 and integration, bridging the range from cognitive psychology to applied research for multi-media applications. A major part of this chapter deals with a variety of research questions related to the temporal relation between audio and video. Other issues of interest are basic spatio-temporal interaction, spatio-temporal effects in audio—visual stimuli — including the ventriloquist effect, cross-modal effects in attention, audio—visual interaction in speech perception and interaction effects with respect to the perceived quality of audio—visual scenes.

In this chapter psycho-physical methods which are useful for both psycho-acoustics and sound-quality engineering will be discussed, namely, the methods of random access, the semantic differential, category scaling and magnitude estimation. Models of basic psycho-acoustic quantities like loudness, sharpness and roughness as well as composite metrics like psycho-acoustic annoyance will be introduced, and their application to sound-quality design will be explained. For some studies on sound quality the results of auditory evaluations will be compared to predictions from algorithmic models. Further, influences of the image of brand names as well as of the meaning of sound on sound-quality evaluation will be reported. Finally, the effects of visual cues on sound-quality ratings will be mentioned.

This chapter provides an overview of quality aspects which are important for telecommunication speech services. Two situations are addressed, the telephone communication between humans and the task-oriented interaction of a human user with a speech-technology device over the phone, e. g., a spoken-dialogue system. A taxonomy is developed for each situation, identifying the relevant aspects of the quality of service. The taxonomies are used for classifying quality features, as perceived by the users of the service, as well as parameters and/or signals which can be measured instrumentally during the interaction. For conversations between humans, relationships can be established between the parameters/signals and the perceptive quality features, thus allowing for prediction of the quality for specific application scenarios. Finally, future efforts necessary for establishing similar prediction models for task-oriented human-machine interaction over the phone are identified.

Sound design constructs audibility of the world. Sounds carry information about the world. When listening to sounds, communication takes place. These are well-known facts for speech sounds, but it is also true for other types of sounds such as music or product sounds. In principle, each acoustic event can be perceived as a sign carrier through which information about the world is communicated. In its ultimate sense, sound designers are engineers of communication . To be successful, they have to take design decisions on the basis of how listeners perceive sounds and of what kind of communication takes place during this event. Suitable sound design requires a special view on acoustic/auditory communication. Among other sciences, semiotics deals with this field.

The term “binaural technique” is used as a cover label here for methods of sound recording, synthesis and reproduction, where the signals in focus are the acoustic signals at the eardrums. If these are presented authentically to listeners, the listeners will obtain acoustic cues which are deemed sufficient for authentic auditory experience — including its spatial aspects. This chapter reviews the basic principles of binaural technique - putting a special focus on results of investigations which have been performed at Aalborg University. These basic principles form the foundation for current utilization of binaural technique at large. They include basic theory, investigations on sound transmission in the ear canal, measurements and post-processing of head-related transfer functions, HRTFs, transfer functions of headphones and their adequate equalization, and results from localization experiments in real life as well as with binaural recordings from real heads and artificial heads. Numerous applications to these methods exist. Some of them will be introduced exemplarily.

Within the last 15 years, hearing instruments have strongly improved due to the application of modern technologies. This chapter provides a look at the possibilities and restrictions of the technologies used and at the signal-processing algorithms available today for the most advanced commercial hearing instruments. Due to ongoing development in semi-conductors the application of even more complex algorithms is expected for the near future. The first part of this chapter focuses on the different designs and chip technologies seen with today’s hearing instrument. Consequently, signal-processing algorithms are reviewed which are applied in digital hearing instruments. Finally, we deal with the components of hearing instruments and with methods for fitting the instruments to the individual’s hearing impairment.