This paper gives HRTF magnitude data in numerical form for 43 frequencies between 0.2---12 kHz, the average of 12 studies representing 100 different subjects. However, no phase data is included in the tables; group delay simulation would need to be included in order to account for ITD. In 3-D sound applications intended for many users, we want might want to use HRTFs that represent the common features of a number of individuals. But another approach might be to use the features of a person who has desirable HRTFs, based on some criteria. (One can sense a future 3-D sound system where the pinnae of various famous musicians are simulated.) A set of HRTFs from a good localizer (discussed in Chapter 2) could be used if the criterion were localization performance. If the localization ability of the person is relatively accurate or more accurate than average, it might be reasonable to use these HRTF measurements for other individuals. The Convolvotron 3-D audio system (Wenzel, Wightman, and Foster, 1988) has used such sets particularly because elevation accuracy is affected negatively when listening through a bad localizers ears (see Wenzel, et al., 1988). It is best when any single nonindividualized HRTF set is psychoacoustically validated using a 113 statistical sample of the intended user population, as shown in Chapter 2. Otherwise, the use of one HRTF set over another is a purely subjective judgment based on criteria other than localization performance. The technique used by Wightman and Kistler (1989a) exemplifies a laboratory-based HRTF measurement procedure where accuracy and replicability of results were deemed crucial. A comparison of their techniques with those described in Blauert (1983), Shaw (1974), Mehrgardt and Mellert (1977), Middlebrooks, Makous, and Gree...

The development of an alternative medium for displaying information in complex humanmachine interfaces is described. The three-dimensional virtual acoustic display is a means for accurately transfering information to a human operator using the auditory modality; it combines directional and semantic characteristics to form naturalistic representations of dynamic objects and events in remotely-sensed or simulated environments. Although the technology can stand alone, it is envisioned as a component of a larger multisensory environment and will no doubt find its greatest utility in that context. The general philosophy in the design of the display has been that the develop-ment of advanced computer interfaces should be driven first by an understanding of human perceptual requirements, and later by technological capabilities or constraints. In expanding on this view, the paper addresses current and potential uses of virtual acoustic displays, characterizes such dis-plays, reviews recent approaches to their implementation and application, describes the research project at NASA Ames in some detail, and finally outlines some critical research issues for the future.

This paper describes a method of presenting structured audio messages, earcons, in parallel so that they take less time to play and can better keep pace with interactions in a human-computer interface. The two component parts of a compound earcon are played in parallel so that the time taken is only that of a single part. An experiment was conducted to test the recall and recognition of parallel compound earcons as compared to serial compound earcons. Results showed that there are no differences in the rates of recognition between the two groups. Non-musicians are also shown to be equal in performance to musicians. Some extensions to the earcon creation guidelines of Brewster, Wright & Edwards (1992) are put forward based upon research into auditory stream segregation. Parallel earcons are shown to be an effective means of increasing the presentation rates of audio messages without compromising recognition rates. 1.

This paper describes the design of user-interface widgets that include non-speech sound. Previous research has shown that the addition of sound can improve the usability of human-computer interfaces. However, there is little research to show where the best places are to add sound to improve usability. The approach described here is to integrate sound into widgets, the basic components of the human-computer interface. An overall structure for the integration of sound is presented. There are many problems with current graphical widgets and many of these are difficult to correct by using more graphics. This paper presents many of the standard graphical widgets and describes how sound can be added. It describes in detail the usability problems with the widgets and then the non-speech sounds to overcome them. The non-speech sounds used are earcons. These sonically-enhanced widgets allow designers who are not sound-experts to create interfaces that effectively improve usability and have coherent and consistent sounds.

Introduction Auditory processing is often given minimal attention when designing virtual environments or simulations. This lack of attention is unfortunate since auditory cues play a crucial role in everyday life. Auditory cues increase awareness of surroundings, cue visual attention, and convey a variety of complex information without taxing the visual system. The entertainment industry has long recognized the importance of sound to create ambience and emotion, aspects that are often lacking in virtual environments. In short, placing someone in a virtual world with an improperly designed auditory interface is equivalent to creating a "virtual" hearing impairment for the user. Auditory perception, especially localization, is a complex phenomenon affected by physiology, expectation, and even the visual interface. Different methods for creating auditory interfaces will be considered. As will be discussed later in this chapter, spatialized audio using headphones is the only audio te

Current user interfaces typically utilise the visual sensory channel to deliver most (if not all) of their information. Given the large quantities of data that are delivered via software application user interfaces,

The current MIDI-based sound system for the distributed virtual environment of NPSNET can only generate aural cues via free-field format in two dimensions. To increase the effectiveness of the auditory channel in NPSNET, a sound system is needed which can generate aural cues via free-field format in three dimensions. The approach taken was to build upon the current NPSNET sound system: NPSNET-PAS [ROES94]. Hardware limitations of NPSNET-PAS sound generating equipment were identified and more capable off-the-shelf sound equipment was procured. In software, a new algorithm was developed which properly distributes the total volume of a virtual sound source to a cube-like configuration of eight loudspeakers. A second algorithm, based on the Precedence Effect, was also developed in an attempt to enhance one s ability to localize a sound source. Synthetic reverberation using digital signal processors was added to enhance perceptual distance of the generated aural cues. The result of this research is a MIDI-based free-field sound system consisting of off-the-shelf sound equipment and computer software capable of generating aural cues in three dimensions for use in NPSNET. This sound system was tested during numerous demonstrations of NPSNET and proved capable of generating eight independent audio channels required for potential output to a cube-like configuration of eight loudspeakers laying the foundation for increasing one s level of immersion in NPSNET.

An empirical study explored the extent to which people can map locations in auditory space to locations on a visual display for four different transformations (or mappings) between auditory and visual surfaces. Participants were trained in each of four transformations: horizontal square, horizontal arc, vertical square, and vertical spherical surface. On each experimental trial, a sound was played through headphones connected to a spatialized sound system that uses a non-individualized head-related transfer function. The participant’s task was to determine, using one transformation at a time, which of two objects on a visual display corresponded to the location of the sound. Though the two vertical transformations provided a more direct stimulus-response compatibility with the visual display, the two horizontal transformations made better use of the human auditory system’s ability to localize sound, and resulted in better performance. Eye movements were analyzed, and it was found that the horizontal arc transformation provided the best auditory cue for moving the eyes to the correct visual target location with a single saccade. 1 Auditory displays are routinely used to keep an operator abreast of what is happening in the visual periphery. Auditory alerts often direct attention to visual displays in cars, aircraft,

A vibrotactile N-back task was used to generate cognitive load while participants were guided along virtual paths without vision. As participants stepped in place, they moved along a virtual path of linear segments. Information was provided en route about the direction of the next turning point, by spatial language (“left, ” “right, ” or “straight”) or virtual sound (i.e., the perceived azimuth of the sound indicated the target direction). The authors hypothesized that virtual sound, being processed at direct perceptual levels, would have lower load than even simple language commands, which require cognitive mediation. As predicted, whereas the guidance modes did not differ significantly in the no-load condition, participants showed shorter distance traveled and less time to complete a path when performing the N-back task while navigating with virtual sound as guidance. Virtual sound also produced better N-back performance than spatial language. By indicating the superiority of virtual sound for guidance when cognitive load is present, as is characteristic of everyday navigation, these results have implications for guidance systems for the visually impaired and others.

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