The Advent of Communication Acoustics in Retrospect

Buenos Aires – 5 to 9 September, 2016 st Acoustics for the 21 Century… PROCEEDINGS of the 22 nd International Congress on Acoustics Communication Acoustics: Paper ICA2016-187 The advent of Communication Acoustics in retrospect Jens Blauert Ruhr-Universität Bochum, Germany, [email protected] Abstract Communication Acoustics is a cover label for those aspects of acoustics that involve relations between the classical fields of acoustics and the information and communication technologies. The usage of the term started around 1974, but it took 42 year until it finally became an explicit topic at the International Congress of Acoustics, namely, here in Buenos Aires at the ICA 2016. In the current talk, the history of Communication Acoustics will be recalled, considering the roles of electro-acoustics, auditory perception and audio-signal processing in the course of the de- velopment of this field. In this context, two areas of application will be taken as examples to discuss the essence of Communication Acoustics, namely, (a) Virtual-Reality (VR) generation and (b) Computational Auditory-Scene Analysis (CASA) ─ both dealing with parametric representa- tions of auditory scenes. In both of these fields the trend can identified of including more explicit knowledge as well as learning algorithms into Communication-Acoustics systems and their com- ponents. For this purpose, proficiency in computational symbol processing is required in terms of scientific craftsmanship, besides pure signal-processing skills Keywords: communication acoustics; communication acoustics, definition of; communication acoustics, history of; nd 22 International Congress on Acoustics, ICA 2016 Buenos Aires – 5 to 9 September, 2016 st Acoustics for the 21 Century… The advent of Communication Acoustics in retrospect 1 Introduction This paper does not present scientific results. It is, in essence, a subjective report by an eye- witness, namely, the author himself, on how he experienced the advent of Communication Acoustics. He had written a PhD thesis and an inaugural thesis on spatial hearing in the 60 th and was, in 1974, appointed professor in Bochum, Germany, with teaching obligations in electrical-field and network theory. When he disclosed to his faculty colleagues that he intended to start a research program in Perceptual Acoustics, they were quite concerned as they did not accept sensory perception as a topic of scientific research. The relevance of this field for the information technologies was not yet recognized, although this author had already proposed the basic idea of perceptual coding [1] at that time. Although it is long established that Acoustics has two aspects to it, the physical, see [2], and the perceptual one, see [3] ─ in fact, the word Acoustics derived from the ancient Greek word for "to hear" (AKOÝEIN ... ak’u:in) ─ engineers had strong reservation regarding the perceptual side of it. Thus, the term Perceptual Acoustics was not accepted, nor was the term Communication Acoustics (sic!), for a research field in engineering, and we had to settle for Electroacoustics. A took years until this attitude changed, and finally the Institute of Communication Acoustics in Bochum was officially established ─ the first of its kind in those days. Nevertheless, this put this author into the position of recognizing his own profes- sional activities as being flanked by two important milestones of modern acoustics, with Com- munication Acoustics right in the middle between the two. 2 Milestone #1 ─ Electroacoustics When this author received his basic university education, most academic teachers in Acoustics were specialized in Electroacoustics ─ for the reason that Acoustics had now taken advantage Figure 1: Milestone #1 − Electrical engineering joined forces with Acoustics of technologies from electrical engineering. However, this could only happen at a large scale after the independent invention of the vacuum triode in by Robert von Lieben and Lee de Forest 2 nd 22 International Congress on Acoustics, ICA 2016 Buenos Aires – 5 to 9 September, 2016 st Acoustics for the 21 Century… [4], although important communication-technology-related inventions (telephone, telegraphone, photographophone) had been made much earlier (Fig. 1). But only now a device was finally available for amplifying “weak” currents. This paved the way for developing applications for a broader public, such as radio, television, public-address systems, and many relevant military applications (e.g., radar). Consequently, the adoption of electrical-engineering technologies by classical acoustics (physical acoustics and perceptual acoustics) marks a milestone of modern acoustics and lead to an enormous upswing in the field. 3 Milestone #2 ─ Communication Acoustics At the beginning of the 60 th , laboratory computers became available, and it was most likely M. Schroeder at Bell Labs, who started their application for acoustic-signal processing at a lar- ger scale. After having listened to his famous talk at the Tokyo ICA (Fig. 2) many of us realized that this will shape the future of acoustics. This author, by the way, spend all his Bochum start- up money (about 600,000 $ in today’s value) for acquiring an 8-bit computer with a one-screen DOS system and 16k (!) floppy disks. For this new field in Acoustics, which developed from an integration of physics, electrical engineering, computers, and perception, the term Communica- tion Acoustics was soon accepted. An operational definition reads as follows: “Communication Acoustics deals with those areas of acoustics which relate to the modern communication and information sciences and technologies.” At least two comprehensive books are meanwhile available in print [5, 6]. Figure 2: Milestone #2 ─ Computers and digital signal processing entered the game Looking at the essence of communication-acoustics research, a foremost task appears to be the analysis and synthesis of auditory objects and scenes, and their representation in parametric form [7, 8]. This leads to two prominent application areas, namely, computational auditory- scene analysis (CASA) and generation of (so-called) virtual reality (VR). We start here with the discussion of the schematic of a bimodal (audio-tactile) VR generator (Fig. 3). Controlled by a world-model, the system renders acoustic and tactile stimuli to the human observer. Thereby it continuously receives information from position trackers [9] mounted on head and hand of the observer. This makes the system interactive ─ what is an important feature, as only interactive 3 nd 22 International Congress on Acoustics, ICA 2016 Buenos Aires – 5 to 9 September, 2016 st Acoustics for the 21 Century… Figure 3: Schematic of a bimodal VR generator [8] systems provide VR ─ what makes them more than just displays. But note that interactivity re- quires fast processing speeds, ideally processing in almost real time. The world model includes parametric representation of the space to be generated, typically based on a tray-tracing [10] or image-source model [11], or a combination of the two [12]. The acoustic signals are presented via headphones [13], and for the tactile rendering a special data glove is needed that employs tactile and thermal actuators. In many applications of virtual-reality generators it is aimed at exposing the observers to situ- ations such that they feel perceptively “present” in them. This is especially important for sce- narios in which the observers are supposed to act intuitively ─ as they would do in a respective real environment. Human–system interfaces which base on the principle of virtual reality have the potency of simplifying human–system interaction considerably. One may think of teleopera- tion systems, design systems and dialog systems in this context, also of computer games. The effort involved in creating perceptual presence is task-depending and depends on user requirements. For example, for vehicle simulators the perceptual requirements are less stringent than for virtual control rooms for sound engineers. In general, virtual reality must appear sufficiently “plausible” to the observer in order to provide perceptual presence. Since VR systems are just about to enter the consumer market, various solutions to this problem can be expected. The schematic shown in Fig. 3 houses, as its core, a “world model”. This is basically a repo- sitory that contains detailed descriptions of the space and of all objects which are to exist in the virtual realty. In one layer of the world model, termed application, rules are listed which regulate the interaction of the virtual objects with respect to the specific applications intended. Further, a central-control layer collects the reactions of the subjects which use the virtual-reality interactively and prompts the system to render appropriate responses. It goes without saying that, in order to render suitable stimuli to the human observer, the system has to make decision based on the actual situation and the tasks assigned to them. Depending on the tasks, this re- quires specific world knowledge and/or capabilities for autonomous learning in order to enable 4 nd 22 International Congress on Acoustics, ICA 2016 Buenos Aires – 5 to 9 September, 2016 st Acoustics for the 21 Century… suitable cognitive functions. Indeed, current implementation of such systems can be distin- guished by the level of intelligence and knowledge that they are furnished with. We shall now discuss the second representative application area of Communication Acoustics as announced

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