Dorte Hammersho

Three-dimensional point-cloud room model in room acoustics simulations

Telepresence applications require communication with the feeling of being together and sharing the same environment. One important task in these applications is to render the acoustics of the distant room for the telepresence system user. This paper presents a fast method for the room geometry acquisition and its representation with a 3D point-cloud model, as well as utilization of such a model for the room acoustics simulations. A room is scanned with a commercially available input device (Kinect for Xbox360) in two different ways; the first one involves the device placed in the middle of the room and rotated around the vertical axis while for the second one the device is moved within the room. Benefits of both approaches were analyzed. The devices depth sensor provides a set of points in a three-dimensional coordinate system which represents scanned surfaces of the room interior. These data are used to build a 3D point-cloud model of the room. Several models are created to meet requirements of differen...

Effects of personal stereo use: pilot results from 20 university students

Modern personal stereo systems have the ability to store thousands of music files in small, relatively low‐cost, compact devices. The popularity and widespread presence of the MP3 player cannot go unnoticed in contemporary society. Given a sufficient noise level and listening duration, consumers are at risk of developing a noise‐induced hearing loss. A study into the effects of personal stereo use will be carried out with the intention of investigating common noise exposure levels in realistic settings, user listening habits and the hearing status in a group of listeners. Noise exposure levels are to be obtained by using the manikin technique described in the ISO 11904‐2 standard. The questionnaire to be presented to interested participants is designed to report personal stereo listening habits and to screen subjects for the hearing status evaluation. The hearing status of selected subjects will be evaluated through the use of conventional and possibly extended high‐frequency audiometry, transient‐evoked ...

Capturing blocked-entrance binaural signals from open-entrance recordings

Binaural recordings enable us to capture all sound attributes including spatial information, room effect, and source characteristics in a given environment. It has been shown that blocked‐entrance binaural recordings provide advantages over open‐entrance recordings, primarily because the blocked‐entrance recordings is not influenced by the ear canal acoustics of the individual for which it is recorded. However, blocking the ear canal for recoding imposes an obvious disruption to normal hearing conditions, which may be unacceptable for applications in which binaural audio capturing is desired but without interfering the individuals hearing and doing. In this work we propose a strategy for the recording of binaural audio with minimal hearing interference, and for transforming these recordings to blocked‐entrance versions that are more suitable for analysis and reproduction of binaural audio in a more general context. To this purpose, equalization filters are derived from the ratio between blocked and open ...

Review of literature on hearing damage by personal stereo

In the 1980s and 1990s there was a general concern for the high levels that personal stereo systems were capable of producing. At that time no standardized method for the determination of exposure levels existed, which could have contributed to overly conservative conclusions. With the publication of ISO 11904‐1:2002 and 11904‐2:2004, previous studies can be viewed in a different light, and the results point, in our opinion, at levels and listening habits that are of hazard to the hearing. The present paper will review previous studies that may shed light over the levels and habits of contemporary personal stereo systems, which can produce even higher levels and are of even wider use.

Evaluation of artificial head recording systems

Artificial head (or dummy head) recording and playback systems are increasingly used. The main advantage of these systems is their ability to reproduce three‐dimensional spatial aspects of sound. However, the exact reproduction of direction has been questioned from time to time. The study presents an objective and subjective evaluation of eight artificial heads. In the objective test, the head‐related transfer functions of the heads were compared to those of humans. Significant deviations were seen for all heads, and none of them can be characterized as a mean, median, or typical head. In the subjective test a panel of listeners indicated direction and distance to sound sources recorded by the head and reproduced by means of carefully equalized headphones. The reproduction of direction was in general poor, especially in the median plane.

Recovery of distortion product otoacoustic emissions (DPOAE) with high time-resolution from a moderate monaural-exposure to 2-kHz in human subjects

The amplitude of distortion product otoacoustic emissions (DPOAE) decreases temporarily after exposure to a sound of moderate level. These changes show similarities to the changes observed in absolute hearing thresholds after similar sound exposures. This paper presents the experimental protocol to study how DPOAEs in human subjects are affected after a monaural exposure of ten minutes to a pure tone of 2 kHz. The experimental protocol allows to measure fine structures of the DPOAE with high time‐resolution in a limited frequency range. Thus, the results give a detailed description of the DPOAE recovery process and can be used to develop a mathematical model of the recovery. This is the first approximation to study the recovery of more complex exposures. [Work supported by the Danish Research Council for Technology and Production.]

Does overexposure modify the fine structure of distortion product otoacoustic emissions

It is investigated, whether the pattern of distortion product otoacoustic emission (DPOAE) fine structure (quasiperiodic variations across frequency) is altered by an acoustical overexposure. DPOAE fine structures are determined in 16 normal‐hearing humans using a high frequency‐resolution and primary levels of L1/L2=65/45 dB. DPOAEs are measured both before and after the subjects are monaurally exposed to a 1 kHz tone lasting for 3 min at an equivalent threshold sound pressure level of 105.5 dB. After the exposure the DPOAE levels are shifted to lower values and recover to the initial levels within 20 min. The DPOAE fine structure pattern is analyzed by an automatic classification algorithm, which determines ripple center frequency, ripple spacing, ripple height, and ripple prevalence. For some individuals, an alteration of some of the parameters could be observed after the exposure, i.e., either a more pronounced or a less pronounced fine structure could be observed after the exposure. Across subjects, ...

Distortion product otoacoustic emission fine structure as an early hearing loss predictor

Otoacoustic emissions (OAEs) are a promising method to monitor early noise‐induced hearing losses. When distortion product otoacoustic emissions (DPOAEs) are obtained with a high‐frequency resolution, a ripple structure across frequency can be seen, called DPOAE fine structure. In this study DPOAE fine structures are obtained from 74 normal‐hearing humans using primary levels of L1/L2=65/45 dB. The subjects belong to groups with different ages and exposure histories. A classification algorithm is developed, which quantifies the fine structure by the parameter’s ripple place, ripple width, ripple height, and ripple prevalence. Temporary changes of the DPOAE fine structure are analyzed by measuring DPOAE both before and after exposing some of the subjects to an intense sound. The characteristic patterns of fine structure can be found in the DPOAE of all subjects, though they are individual and vary from subject to subject within groups. The results do not indicate that the DPOAE fine structure alters with t...

Influence of the sweeping direction of the primaries f1 and f2 in the assessment of distortion product otoacoustic emissions (DPOAEs) fine structure

It was studied if the sweeping direction of the primaries f1 and f2 influences fine structure measurements of the 2f1−f2 distortion product otoacoustic emission (DPOAE). Two different methodologies named DPOAE5ASC (ascending sweep) and DPOAE5DES (descending sweep) were implemented with the commercial system ILO96. Both methods perform fine structure measurements in the same frequency range (1.4–6 kHz) with L1/L2=65/45 dB, f2/f1=1.22 and 0.7 s averaging time per primary presented. DPOAE fine structures were measured in the right ear of 14 normal‐hearing subjects with both methods in a balanced experiment and without refitting the sound probe. Results showed that the two methods are highly repeatable and able to detect fine structures even in subjects with low S/N. However, when DPOAE5ASC measurements are compared with DPOAE5DES, fine structures appear shifted and the level contour is altered. A minor level difference was inadvertently induced due to differences in the level calibration procedure of the two...

Time characteristics of distortion product otoacoustic emissions recovery function after moderate sound exposure

Exposure to sound of moderate level temporarily attenuates the amplitude of distortion product otoacoustic emissions (DPOAEs). These changes are similar to the changes observed in absolute hearing thresholds after similar sound exposures. To be able to assess changes over time across a broad frequency range, a detailed model of the recovery time characteristics is necessary. In the present study, the methodological aspects needed in order to monitor changes in DPOAEs from human subjects measured with high time resolution are presented. The issues treated are (1) time resolution of the measurements, (2) number of frequency points required, and (3) effects in fine structures, are they affected with the exposure? [Work supported by the Danish Research Council for Technology and Production.]