Index of content:
Volume 30, Issue 8, August 1958
Changes in Cochlear Endolymphatic Oxygen Availability, Action Potential, and Microphonics during and following Asphyxia, Hypoxia, and Exposure to Loud Sounds30(1958); http://dx.doi.org/10.1121/1.1909734View Description Hide Description
In order to evaluate the role played by endolymphatic hypoxia on deafness due to exposure to loud sounds, continuous recordings of oxygen availability, action potential, and microphonics were taken during asphyxia, “chronic hypoxia,” and after loud sounds. The curves so obtained are compared and show that hypoxia may play an important contributory role in the temporary losses of heating following loud sounds. Possible mechanisms of auditory trauma are reviewed briefly.
30(1958); http://dx.doi.org/10.1121/1.1909736View Description Hide Description
Solutions of glucose oxidase and its substrate were injected into the scalae to render the organ of Corti hypoxic without affecting oxygen tension in the stria vascularis. It was thus possible to depress action potentials and microphonics, leaving the dc potential largely unaffected, to suppress entirely the action potential of a tone pip of 12 000 cps without similarly suppressing that of 1000 cps, and to diminish the microphonics in one turn without detecting the decrease with an electrode placed in another turn or against the round window. These results were taken to show that the dc potential originates in the stria vascularis, that a tone of 12 000 cps elicits an action potential only in the first cochlear turn, and that a unipolar electrode records only from a limited distance.
30(1958); http://dx.doi.org/10.1121/1.1909738View Description Hide Description
What is the “trading relationship” between intensity and duration of exposures to loud sound in producing a given magnitude of temporary threshold shift (TTS)? Examination of the literature led to the hypothesis that duration is about twice as important as intensity: Two exposures should produce the same TTS if one exposure were one‐fourth the sound level (6 db less) and twice the duration of the other exposure. The hypothesis was tested on 12 human ears with thermal noise exposures ranging from 130 db SPL for 1 min to 94 db SPL for 64 min. In this series each doubling of duration was associated with a fourfold or 6 db decrease in sound level. TTS was measured at 2000, 4000, 6000, and 8000 cps. If the hypothesis were true, all exposures should have produced the same TTS. Actually the obtained average TTS, 5 min after exposure, described an inverted U‐shaped function when plotted by increasing duration of exposure. The conditions from 118 db for 4 min through 100 db for 32 min produced roughly similar amounts of TTS, while the other conditions produced substantially less TTS. The shapes of the recovery curves differed systematically: At 4000 cps, the TTSs 20 sec after exposure were in perfect rank‐order agreement with intensity of exposure, while from about 2 min to 10 min the inverted‐U rank order was apparent.
30(1958); http://dx.doi.org/10.1121/1.1909740View Description Hide Description
Forward and backward curved blade centrifugal fans as noise sources were subjected to an extensive study, measurements being made in a duct with an acoustic termination. The data obtained support the following conclusions:
(1) The noise output from each homologous series of fans can be defined by one V‐shaped specific noise power vs log specific speed curve, with minimum close to maximum static efficiency.
(2) Fan outlet noise power at maximum fan efficiency approximates 10−5 times the input fan power.
(3) The noise origin is primarily blade and air flow boundary turbulence.
30(1958); http://dx.doi.org/10.1121/1.1909742View Description Hide Description
The mechanical recognition of ten spoken words (the digits) with near‐perfect precision has been demonstrated under laboratory conditions for a single talker after optimum circuit adjustment for his voice. Such word recognition points to the possibility of automatic voice writing and other voice‐controlled operations.
The device described is based on two principles—the recognition of sustainable patterns of power versus frequency in speech, and the recognition of the durations of such phonetic patterns in words.
An alphabet of only ten patterns is proven adequate for limited word recognition, at least in the case of a single talker. The successful performance of the ten‐word digit recognizer for voice dialing of telephone numbers was recorded on a motion picture film shown in the oral presentation. Data from the film are discussed in this paper.
This paper describes a working model of a phonetic pattern recognizer built at Bell Telephone Laboratories based on a detailed power‐frequency spectrum analysis. Tests, to be discussed, indicate that this device, which supersedes an earlier model, leads to almost perfect digit recognition when set for a particular voice. The device also offers outstanding possibilities in speech transmission. The former application will be described in this paper and the latter in a companion paper.
30(1958); http://dx.doi.org/10.1121/1.1909744View Description Hide Description
Syllabic spectral patterns of continuous speech have been classified into a finite alphabet through an automatic recognition process built into a “phonetic vocoder.” The classified spectra were then used to synthesize corresponding sounds approximating the original phonetic content, within broad limits. The principle of phonetic recognition can be applied to realize a maximally efficient coding of speech, considering only the phonetic content. The corresponding frequency band is about 50 cps, a 6‐fold reduction over the frequency‐band vocoder. Also, the recognition process assures that spoken words can be printed automatically as phonetic text.
Speech processed with the phonetic vocoder described here was obtained using an alphabet of only four consonants and six vowels. Nonetheless, limited vocabulary transmission was demonstrated over a band of about 100 cps indicating the feasibility of this coding method. Articulation figures of over 95% were measured using the spoken digits as test material. For a larger vocabulary of monosyllabic words, about 50% intelligibility was found in a limited test. Spectrograms of the vocoder input and output are compared.
30(1958); http://dx.doi.org/10.1121/1.1909746View Description Hide Description
A basic method of speech synthesis is described in which discrete segments of recorded utterances are joined together to produce continuous speech. The segments are characterized as (a) containing parts of two phones with their mutual influence in the middle of the segment, and (b) beginning and ending at the phonetically most stable position of each phone. All segments containing the same articulatory sequence have been defined as a dyad. The method of synthesis described includes not only articulatory phones, but also intonation, stress, and duration. A large number of segments is required and various techniques of obtaining the segments for speech synthesis are discussed. The method is limited to a specific dialect, and practically it is limited to a single speaker.
30(1958); http://dx.doi.org/10.1121/1.1909747View Description Hide Description
The inventory of segments required to synthesize an idiolect of American speech from recorded utterances has been partially investigated. A total of 43 phonetic units, including a unit of silence, is found essential. These units represent some of the major allophones of the phonemes of the idiolect. To obtain the segments, utterances are contructed with the desired sequence of the two phonetic units and with the proper intonation and stress environment. The utterances are recorded on magnetic tape, and the desired boundaries of the segments are determined by means of a technique employing a sound spectrograph. An attempt is made to match harmonics, formants, and amplitude envelopes between adjacent segments. To synthesize the idiolect it is estimated that an inventory of about 8500 segments is required. A sentence synthesized from over 40 such segments is demonstrated.
30(1958); http://dx.doi.org/10.1121/1.1909749View Description Hide Description
Magnetostrictive properties of cobalt‐substituted nickel ferrous‐ferrite were investigated to determine its suitability for use in electromechanical transducers. Toroidal samples were sintered at 1400°C and cooled by quenching in air. The following parameters were measured and compared with the corresponding parameters of previously investigated magnetostrictivematerials: electromechanical coupling coefficient, reversible permeability, dynamic magnetostrictive constant, maximum stress, and the product of characteristic frequency times the thickness squared.
The results of the investigation indicate that a ferrite having the formula with 0.015 ⩽ x ⩽ 0.04 and 0.02 ⩽ y 0.065 moles per mole of ferrite meets the requirements for transducer applications. The electromechanical coupling coefficient for this range of compositions varies from 0.28 to 0.37. The value of the characteristic frequency times the thickness squared (4200) is approximately 1700 times that of nickel. The maximum stress increases with ferrous iron, reaching a value of 68×106 dynes/cm2 for 0.06 mole of FeO per mole of ferrite as compared with 32×106 dynes/cm2 for no ferrous iron.
30(1958); http://dx.doi.org/10.1121/1.1909751View Description Hide Description
The optical method used by Loeber and Hiedemann for the study of stationary ultrasonic waves has been adapted to the study of progressive waves. Three methods are described by which one may determine the presence of distorted wave forms in liquids. Distorted wave forms caused by finite amplitude effects are shown to be present in liquids and the increase of wave form distortion with distance is shown for water and carbon tetrachloride.
30(1958); http://dx.doi.org/10.1121/1.1909753View Description Hide Description
Three optical methods, formerly only used for isotropic media, are applied to find the ultrasonic velocities in sapphire. From the results the elastic constants are calculated for this crystal. The elastic moduli are determined from measurements of ultrasonic velocities in different crystallographic directions, and Young's modulus is plotted as function of these directions.
30(1958); http://dx.doi.org/10.1121/1.1909755View Description Hide Description
The effect on the generation of jet noise by the secondary air induction of a modified jet nozzle is analyzed. It is shown that the combination of the secondary air with the primary jet air creates a new jet stream of larger area, lower velocity, and lower noise generation. The decrease in noise radiation is found in terms of the area of the combined jet stream. Detailed check of the theory is not possible at present because measurements of the areas of the combined jet streams have not been generally made along with measurements of the noise. However, it is possible to estimate the upper limit of the appropriate jet stream area in order to obtain the upper limit on noise reduction. The upper limit on noise reduction obtained from the theory is consistent with existing measurements. Qualitative conclusions from the theory with respect to the spectrum and directivity of the noise radiated by jets with modified nozzles are in accord with measurements.
30(1958); http://dx.doi.org/10.1121/1.1909757View Description Hide Description
Observations were made on audio‐frequency sounds propagating through a gaseous medium containing small solid particles in suspension. Two effects were observed, the attenuation and the dispersion. The measurements were carried out by sending short trains of sine waves through the particle‐filled gas and observing the changes in the transmitted train of waves after the particles settled out of the gas. The variation in arrival time of the pulse was used to determine the velocity change caused by the suspended particles. Changes in the amplitude of the received pulse made it possible to determine the additional attenuation due to the suspended particles.
The variations of the attenuation and velocity with frequency due to the particle‐filled gas were obtained and the results compared with theory. The measured attenuation was found in good agreement with existing theory. The observed dispersion satisfactorally accounted for by a theory that is introduced in this paper. The attenuation theory takes into account enhanced viscous and thermal losses caused by the suspended particles. The dispersion theory predicts the velocity shift resulting from changes of the heat capacity and density of the gas containing the suspended particles,
30(1958); http://dx.doi.org/10.1121/1.1909759View Description Hide Description
This study deals with the scattering of plane compressional and shear elastic waves incident obliquely on an infinitely long nondissipative cylindrical elastic discontinuity in an isotropic solid.Equations whose solutions are the coefficients in series expressions for the scatteredwaves are derived for the case of scattering at an elasticsolid cylinder embedded in a different solid medium. From these equations are obtained those governing scattering at a fluid‐filled cylindrical bore, and at an empty bore.
In general, when a wave of either the compressional or shear type is incident on an elastic discontinuity, scatteredwaves of both types are produced, a process known as “mode conversion.” A simple relation is shown to exist between the two far‐zone distributions‐in‐angle, and between the two scattering cross sections for the waves undergoing mode conversion in the scattering of compressional and normally polarized shear waves incident normally upon either a fluid‐filled or an empty bore.
For an empty bore whose diameter was comparable with a wavelength in the solid, computed distributions‐in‐angle for the scattering of normally incident compressional and normally polarized shear waves were verified experimentally. Measurements were also made of the scattering of compressional waves at a fluid‐filled bore in a solid, and of the far‐zone directivity patterns of some compressional and shear wave piezoelectric source crystals radiating into a solid medium.
30(1958); http://dx.doi.org/10.1121/1.1909761View Description Hide Description
The plane‐strain vibrations of a thick‐walled hollow cylinder are investigated in the framework of the linear theory of elasticity. Approximate expressions for the frequencies of free modes are derived for moderately thick shells. The transition from the shell vibrations to the Pochhammer vibrations of a solid cylinder is investigated by means of a numerical solution of the frequency equation using an IBM 704 digital computer.
30(1958); http://dx.doi.org/10.1121/1.1909763View Description Hide Description
The role that is played by a schematic diagram in the analysis of a mechanical system is discussed. Having defined the function of these diagrams, it is then possible to collect together those ideas and principles on the basis of which a systematic technique for constructing these diagrams can be evolved. Illustrations of the process are given.