Francis M. Wiener

Bio: Francis M. Wiener is an academic researcher. The author has contributed to research in topics: Diffraction & Sound pressure. The author has an hindex of 8, co-authored 14 publications receiving 430 citations.

The Pressure Distribution in the Auditory Canal in a Progressive Sound Field

Abstract: The variation of the sound pressure along the auditory canal was determined experimentally on a number of subjects, male and female, placed in a progressive sound field This was accomplished by insertion of a small flexible probe microphone at various positions along the auditory canal The subjects were placed in front of a loudspeaker in a room free from acoustic wall reflections The free sound field at the subjects' location was essentially that of a plane progressive wave The measurements were carried out over the significant range of audiofrequencies for various orientations in azimuth of the subjects with respect to the sound source The sound pressure at the eardrum is found to be greater than the free‐field pressure The average ratio of these two quantities is a function of frequency, and reaches values of about 20 db in the vicinity of 3000 cps The human ear is thus an effective acoustic “amplifier” The increase in sound pressure at the eardrum over the free‐field pressure is caused by a combination effect of diffraction by the head and pinna and resonance in the auditory canal The measurements of the sound pressures at several other positions along the auditory canal serve to separate these two phenomena to a certain extent and to furnish additional information about the pressure distribution Most of the data were obtained with a group of male subjects, but measurements on a few women did not show any marked discrepancies

Sound Diffraction by Rigid Spheres and Circular Cylinders

Abstract: The results of calculations of the pressure distribution on the surface of a stationary rigid sphere and a stationary rigid circular cylinder of infinite length, when exposed to a plane progressive sound wave, are compared with experiment. A small probe microphone was used to measure the sound pressures on the surface of the obstacles in a room essentially free from acoustic wall reflections under a variety of experimental conditions. The sound pressures p on the surface are conveniently expressed relative to the free‐field pressure p0 in the undisturbed incident wave.In the case of the sphere, reasonably good agreement was obtained between theory and experiment in the range of 13

The Diffraction of a Progressive Sound Wave by the Human Head

Abstract: An earlier paper described the distribution of sound pressure in the auditory canals of a number of subjects in a plane progressive sound field. At a given frequency, the ratio of the sound pressures at the eardrum and at the entrance to the ear canal was found to be greater than unity and essentially independent of the orientation of the observer with respect to the sound source, as might be expected from theory. With this ratio known, it is possible to determine, with relative ease, the sound pressures at the eardrum as a function of azimuth from pressure measurements near the entrance to the auditory canal. By positioning a probe microphone at the entrance to the ear canal and comparing the sound pressures there with the free‐field pressures at the subject's location an estimate of the obstacle effect of head and pinna is arrived at. Adding the known pressure increase in the auditory canal yields a measure of the total obstacle effect of the human head and auditory canal. The subjects were placed in front of a loudspeaker in a room essentially free from acoustic wall reflections. The measurements of the sound pressure at the entrance of the left auditory canal and in the free field in the absence of the subject were carried out by means of a small probe microphone in the frequency range extending from 200–6000 c.p.s. A range of azimuths of 360 degrees was covered in 45‐degree steps. If it is assumed that the two auditory canals are alike and that the head is symmetrical about the median plane, the ratio of the sound pressures at the left and right eardrums can be readily computed from these data. This ratio is of importance in the mechanism of binaural localization. The average for six male subjects was compared with the values obtained by Sivian and White from threshold measurements and was found to be in fair agreement.

On the Intelligibility of Bands of Speech in Noise

Abstract: Articulation tests were conducted with a large number of communication systems having band widths ranging from about one‐half octave to a system covering the entire range of speech frequencies. The systems were linear and their responses were approximately uniform over the pass band, with sharp cut‐offs at either end. The acoustic gain of the systems was expressed relative to the transmission of speech through one meter of air between talker and listener. Two spectra of masking noise were used, and each system was tested over a wide range of speech‐to‐noise ratios. In one group of experiments the speech was filtered before mixing with noise and in the other group both the speech and the noise were passed through the same filter. For each of the band‐pass systems a relation between syllable articulation and level of received speech was obtained. From these gain functions, families of equal‐articulation contours may be derived. These contours show, for example, how the gain must be changed for a given change in the band width of a system in order to maintain a constant articulation score.

In Search of the Missing 6 Db

Abstract: The unexplained difference in sound pressure in the ear canal which appears to exist when equally loud low frequency tones are presented alternately from an earphone and from a loudspeaker has bedeviled acousticians for many years and, unfortunately, still continues to do so. There are presented here the results of some of the measurements carried out at the Bell Telephone Laboratories which show the magnitude of the effect and various attempts at explaining it. While no satisfactory explanation has been found, it is hoped that publication of these results will stimulate interest in the problem.

Speech Analysis, Synthesis and Perception

Abstract: The first edition of this book has enjoyed a gratifying existence. 1s sued in 1965, it found its intended place as a research reference and as a graduate-Ievel text. Research laboratories and universities reported broad use. Published reviews-some twenty-five in number-were universally kind. Subsequently the book was translated and published in Russian (Svyaz; Moscow, 1968) and Spanish (Gredos, S.A.; Madrid, 1972). Copies of the first edition have been exhausted for several years, but demand for the material continues. At the behest of the publisher, and with the encouragement of numerous colleagues, a second edition was begun in 1970. The aim was to retain the original format, but to expand the content, especially in the areas of digital communications and com puter techniques for speech signal processing. As before, the intended audience is the graduate-Ievel engineer and physicist, but the psycho physicist, phonetician, speech scientist and linguist should find material of interest."

Headphone simulation of free‐field listening. I: Stimulus synthesis

Abstract: This article describes techniques used to synthesize headphone-presented stimuli that simulate the ear-canal waveforms produced by free-field sources. The stimulus synthesis techniques involve measurement of each subject's free-field-to-eardrum transfer functions for sources at a large number of locations in free field, and measurement of headphone-to-eardrum transfer functions with the subject wearing headphones. Digital filters are then constructed from the transfer function measurements, and stimuli are passed through these digital filters. Transfer function data from ten subjects and 144 source positions are described in this article, along with estimates of the various sources of error in the measurements. The free-field-to-eardrum transfer function data are consistent with comparable data reported elsewhere in the literature. A comparison of ear-canal waveforms produced by free-field sources with ear-canal waveforms produced by headphone-presented simulations shows that the simulations duplicate free-field waveforms within a few dB of magnitude and a few degrees of phase at frequencies up to 14 kHz.

Virtual pitch and phase sensitivity of a computer model of the auditory periphery. I: Pitch identification

Abstract: Licklider made his original suggestion in an attempt to explain the human ability to perceive the pitch of a complex tone even though that tone contained no spectral component corresponding to that pitch. He rejected the prevailing theory (Fletcher, 1924) that distortion products of nonlinear cochlear responses could wholly explain the phenomenon. He pointed to the fact that the waveform envelope of unresolved harmonic components could be used to extract pitch information if an autocorrelation analysis could be performed. He thought that this might be achieved by a delay line mechanism at a low level in the auditory nervous system. His theory depended on the idea that the harmonic com

Range dependence of the response of a spherical head model

Abstract: The head-related transfer function (HRTF) varies with range as well as with azimuth and elevation. To better understand its close-range behavior, a theoretical and experimental investigation of the HRTF for an ideal rigid sphere was performed. An algorithm was developed for computing the variation in sound pressure at the surface of the sphere as a function of direction and range to the sound source. The impulse response was also measured experimentally. The results may be summarized as follows. First, the experimental measurements were in close agreement with the theoretical solution. Second, the variation of low-frequency interaural level difference with range is significant for ranges smaller than about five times the sphere radius. Third, the impulse response reveals the source of the ripples observed in the magnitude response, and provides direct evidence that the interaural time difference is not a strong function of range. Fourth, the time delay is well approximated by well-known ray-tracing formula due to Woodworth and Schlosberg. Finally, except for this time delay, the HRTF for the ideal sphere appears to be minimum-phase, permitting exact recovery of the impulse response from the magnitude response in the frequency domain.

Head-Related Transfer Functions of Human Subjects

Abstract: Head-related transfer functions (HRTFs) were measured on 40 human subjects for 97 directions of sound incidence, covering the entire sphere Individual HRTF data for the median, horizontal, and frontal planes are presented in the frequency domain Measurements were made synchronously at both ears, thus making the time representations, that is, the head-related impulse responses (HRIRs), valid also when interaural time differences are considered The measurements were made at the entrance to the blocked ear canal Sound at this point contains full spatial information, and the interindividual variation is lower than at the open ear canal