摘要:

This paper describes a scheme for the rule synthesis of speech in which words spoken in isolation were spliced after they were modified by rule. The input to this scheme consists of a typed text accompanied by phrase boundary information. The words spoken in isolation were recorded and analyzed into parameters from which these words can be synthesized after they have been modified. These modifications consisted of (1) a compression of word duration appropriate for continuous speech: however, the same shortened duration is used in all contexts; (2) minimal changes for amplitude and between‐word coarticulation; and (3) pitch determined by context‐dependent pitch rules. Pitch rules have been developed to deal with complex sentences whose phrase structure is known. The resulting paragraph is played as an example of the quality of synthetic speech.

ISSN:0001-4966    

DOI:10.1121/1.3437990

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

An automatic voice response system is described which is capable of servicing up to ten independent output channels in real time. The system is implemented on a NOVA 800 minicomputer. Individual words and phrases are coded at a 24 000 bits/sec rate using adaptive, differential pulse‐code modulation (ADPCM) techniques, and are stored on a fixed‐head disk as a random‐access vocabulary. The system was designed so that it is possible to create a new vocabulary for the system automatically from an analog tape recording with minimal operator intervention. Initial applications of the system are in computer‐aided voice wiring and automatic directory assistance.

ISSN:0001-4966    

DOI:10.1121/1.3437998

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

Noise control programs in production metal machining and forging operations produced significant reductions of noise levels. Interaction with production engineering personnel contributed very much to the achieved successes. Operator exposure to high noise levels was the result of overlapping intermittent sources. Principal noise offenders were airjets, hydraulics, steel impact on steel tables and conveyers, furnace airjets, metal machining, TEFC electric motors, and fans. Management strived to meet 85 dBA (U. S. Army Tech. Bull. MED 251) and 90 dBA (OSHA) levels without regard for exposure time. Operator exposure and source identification was obtained by taping and statistically analyzing noise levels at operator positions. Thorough testing was undertaken before implementation. In the cases studied, increased room absorption was of little value regardless of distance. This was determined through studies of sound field from portable sound sources, impulse techniques, and standard calculations. Reductions of 20 dBA were achieved by installing small resistive and dispersive mufflers on pneumatic controls. Steel impact noise was reduced 15 dBA with combined low durometer rubber and unconstrained viscoelastic damping. Furnace fan noise was reduced by using low‐pressure mufflers on the fan intake, and by relocating fans. Directional electric motor fan noise was reduced by using mufflers.

ISSN:0001-4966    

DOI:10.1121/1.3438002

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

Authority for the implementation of hearing conservation programs within the Department of the Army is established in Army Regulation 40‐5, “Preventive Medicine.” This regulation directs all Army installations to institute and administer active hearing conservation programs subject to frequent inspection and review. In addition, Department of the Army Circular 40‐2 places command emphasis on all phases of the program. Guidance and policies for the conduct of hearing conservation programs are set forth in Technical Bulletin (Medical) 251, “Noise and Conservation of Hearing.” TB MED 251 specifies (1) noise exposure criteria more stringent than those of OSHA, (2) noise hazard evaluation methodology, (3) engineering noise control techniques, (4) personnel protective measures, (5) administrative and clinical procedures for audiometric evaluations, (6) organization of health education program, and (7) the role of command, medical, and supervisory personnel in the conduct of the program. Although these policies are prescribed primarily for occupational noise exposure, there is overlap into nonoccupational activities of personnel. Additional Army documents provide noise emission standards for the procurement of Army equipment.

ISSN:0001-4966    

DOI:10.1121/1.3438006

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

Jamming experiments were conducted to assess the effectiveness of several different types of signals for interfering with the ability of echolocating bats (Eptesicus fuscus) to discriminate target range. Random interfering noise covering the bat's sonar bandwidth of 25–50 kHz must be sufficiently intense for the echo signal‐to‐noise ratios to approach 0 dB before marked breakdown of echolocation occurs. This is true for continuous noise, intermittent noise, and for noise incorporating internal correlation at the same period as the travel time of sounds going to and from the targets. FM interference is 30 to 40 dB more effective in jamming the bat than random noise of the same spectrum. The results suggest that the bat's sonar receiver applies frequency‐sweep criteria to incoming sounds to decide whether potential echoes are present. Neurons with properties appropriate to this filtering function, analogous to motion detection in vision, are known to exist in the bat's auditory nervous system.

ISSN:0001-4966    

DOI:10.1121/1.3438009

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

Sixteen vocalizations from four parakeets were acoustically analyzed. A call usually lasted 140–160 msec and contained between seven and nine notes. The power spectrum of the call indicated that most of the energy was contained in a narrow band of frequencies between 2.0 and 4.0 kHz. These frequencies were also the region of best sensitivity in the parakeet audibility curve. A time‐frequency spectrum was also obtained by measuring the frequency of the first cycle in successive 1.0‐msec steps throughout the call. This analysis revealed that the calls could be discriminated on the basis of whether the first or last note contained relatively pure frequencies. The “constancy of intonation” (Δf/f) was determined for these notes by calculating the standard deviation of the within‐note frequency variations (Δf) and dividing it by the center frequency (f). The “constancy of intonation” was only one to two times larger than the frequency DLs in this species and supports the hypothesis that vocalization performance is related to hearing capacity in birds.

ISSN:0001-4966    

DOI:10.1121/1.3438016

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

This study is part of an overall effort to understand the evolution of the central auditory system. The tree shrew was studied because of its unique status in phylogeny—it resembles some of the earliest primates. Three methods of defining auditory cortex were compared: (1) cytoarchitecture of the cortex, (2) projections from the medial geniculate nucleus to the cortex, and (3) evoked potentials at the cortex in response to auditory stimuli. Analysis of cytoarchitecture revealed an area of neocortex that resembles primary auditory cortex in other mammals. Anterograde degeneration techniques showed that the projections from the medial geniculate nucleus to the cortex were coextensive with the area defined by cytoarchitecture. The main projection within this cortical area was to layer IV. Using macroelectrodes to record evoked potentials, it was found that this area of neocortex has a short latency response to auditory stimuli. We conclude that we have identified primary auditory cortex in the tree shrew. [Supported by grants from NSF and NIH.]

ISSN:0001-4966    

DOI:10.1121/1.3438019

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

Measurements of the ambient noise background have been made with a string of seven hydrophones 200 ft long. Data were collected at a number of depths throughout the water column at a deep water site north of St. Croix, Virgin Islands. The time delay correlograms obtained confirm a binary model for the sources of ambient noise: a low‐frequency type arriving preferentially from near‐horizontal directions, and a high‐frequency type arriving from near‐vertical directions. No variation in coherence with depth was observed. The correlograms constantly fluctuate in amplitude and peak time delay, indicating that the coherence and therefore the directionality are time‐variable properties of the ambient background. Coherence measurements are an alternate, and in some ways a preferable, approach to obtaining the data needed for the optimum design of arrays to operate in the real‐world noise background.

ISSN:0001-4966    

DOI:10.1121/1.3438024

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

A towed array is modeled as a periodic arrangement of identical fluid‐filled hose modules supporting two types of longitudinal waves —extensional waves in the hose wall and resonant breathing waves in the hose‐and‐fluid combination [D. Chase, BBN Rep. 2408 (1972)]. These waves are coupled at the module termini (end shells) where velocities in both types of waves coincide. The net force on an end shell is the sum of forces due to the arrival of both types of waves generated by vibrations of the two adjacent end shells. This dual‐wave model is analogous to a system of masses connected by two springs of different stiffness. End shell motions are described by a superposition of “velocity amplitude waves” of frequency‐dependent phase velocity propagating through them. If resonant breathing waves are lightly damped, in certain frequency intervals these waves are highly damped due to force cancellation. Within such stop bands, an array will be quiet in a narrow‐band sense. Many features of measured low‐frequency self noise are predicted by this model. [Supported by Naval Ship Systems Command.]

ISSN:0001-4966    

DOI:10.1121/1.3438030

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

The effectiveness of highway noise barriers and the effect of highway noise on high buildings depend on the directivity of the noise source. An experiment was designed to determine the directivity pattern of trucks at highway speeds in a vertical plane. An array of microphones was placed on a vertical tower and was used to record the noise generated by trucks driving by on a nearby freeway. The speed was measured and the characteristics of each vehicle were noted. The results show that trucks exhibit an almost omnidirectional pattern, at least up to 45° from the horizontal, independently of the type of truck or type of exhaust. This conclusion is compatible with the results obtained elsewhere for passenger cars. [This study was supported by the National Cooperative Highway Research Program Project 3‐7. The opinions and findings expressed or implied in this paper are those of the author. They are not necessarily those of the Highway Research Board, the National Academy of Sciences, the Federal Highway Administration, the American Association of State Highway Officials, nor of the individual states participating in the National Cooperative Highway Research Program.]

ISSN:0001-4966    

DOI:10.1121/1.3438035

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP