摘要:

The intelligibility of the speech received over a communication system is usually expressed in terms of one or another measure such as the vowel or the consonant articulation, the average speech sound articulation, the syllable articulation, the word articulation, or the sentence intelligibility. The present paper establishes relationships among several of these measures and the articulation index. Relationships based upon statistical considerations are compared with the results of observations. Functions are developed which permit the calculation of articulation index and hence of articulation for communication systems which include a wide variety of responseversusfrequency characteristics and of noise conditions, as well as several special types of distortion. Although the treatment is predominantly empirical, the functions and processes are closely related to various fundamental properties of speech and hearing. Four principal series of articulation tests are cited in detail, some of which have been described in published articles by various persons. The response and the noise, if any, are given for each of these cases and the observed articulations are compared with values calculated by the method here presented. The application of the computational method to the perception of speech by deafened persons is reserved for a subsequent paper. A “Foreword” to the present paper describes the historical importance of articulation tests in the Bell Telephone System.

ISSN:0001-4966    

DOI:10.1121/1.1906605

出版商:Acoustical Society of America    

年代:1950

数据来源: AIP

摘要:

The physiological motions involved in speaking can be indicated to the eye or to the ear. For the eye suitably chosen symbols may be written to indicate the physiological positions assumed informing each sound; for the ear synthetic sounds may be produced by motions in a mechanism built to simulate the speech organs. The degree of phonetic success may be estimated in the case of the visible symbols by listening to sounds formed when the indicated physiological processes are carried out, and in the case of the speech‐simulating mechanism by comparing the synthetic speech produced to normally spoken speech. Significant advances along both the visual and the aural lines are described from earliest times down to the present.Wolfgang von Kempelen produced the first speaking machine worthy of the name around 1780. This paper gives his background, a description of the apparatus he built, and a discussion of the methods used in producing the various sounds, fitting his work into the over‐all picture of speech‐imitating devices from the speaking of idols of ancient times down to the automatic electrical reconstructing of speech in the vocoder. For portraying to the eye the physiological characteristics of speech there are discussed the more outstanding methods from claimed symbolic alphabets of ancient languages down to the recent spectrographic visible speech.

ISSN:0001-4966    

DOI:10.1121/1.1906583

出版商:Acoustical Society of America    

年代:1950

数据来源: AIP

摘要:

This paper concerns the effects of interrupting speech waves—turning them on and off intermittently or masking them with intermittent noise—upon their intelligibility. The effects were studied with various rates of interruption and with the speech left undisturbed various percentages of the time. Tests were conducted (1) with speech turned on and off in quiet, (2) with continuous speech masked by interrupted white noise, and (3) with speech and noise interrupted alternately, the speech wave being turned on as the noise wave was turned off, and vice versa.(1) When the speech wave is turned on and off infrequently, the percentage of the message that is missed is approximately the same as the percentage of time the speech is off. When the interruptions are periodic and occur more often than 10,000 times per second, the interruptions do not interfere with the reception of the message. In the quiet it is easy to understand conversational speech so long as the interruptions occur more than 10 times per second.(2) When continuous speech waves are masked by noise that is interrupted more than 200 times per second, intelligibility is independent of the interruption frequency and of the percentage of time the noise is on, provided the ratio of average speech power to average noise power is held constant. Interrupted masking noise impairs intelligibility least if the frequency of interruption is about 15 per second.(3) When interrupted speech and interrupted noise alternate at frequencies below 10 alternations per second, the noise does not impair intelligibility. At higher frequencies of alternation the temporal spread of masking becomes appreciable.The general features of these results are approximately the same whether the interruptions occur periodically or at random.

ISSN:0001-4966    

DOI:10.1121/1.1906584

出版商:Acoustical Society of America    

年代:1950

数据来源: AIP

摘要:

Groups of 23 males read 12 test phrases in each of eight rooms. The rooms represented two sizes, shapes, and reverberation times. Microphones led to two meters that registered vocal intensity and, in one instance, duration of the phrases. Each set of measurements was treated by analysis of variance. Both rate and intensity of reading were affected by the size and reverberation time of the room and not by the shape. Rate was significantly slower in the larger and the less reverberant rooms. Apparently vocal intensity was greater in the smaller and less reverberant rooms; and readers consistently increased their intensity as they read the 12 phrases in the less reverberant rooms. Differences in this regard, occasioned by the sound treatment of the rooms, were highly significant.

ISSN:0001-4966    

DOI:10.1121/1.1906585

出版商:Acoustical Society of America    

年代:1950

数据来源: AIP

摘要:

In the past loudness patterns have been based on the masking effect of one sound on another. For complex sounds having distributed energy spectrums this method appears to be valid. For sounds with single frequency components the method is thought to be in error due to the formation of beats and modulation products between the primary tone for which a pattern is desired and the probe tone which is used to determine the pattern details. To avoid these difficulties in the present tests, the probe tone was presented after the primary tone was turned off. The resulting residual masking patterns differ in a number of important respects from patterns based on the simultaneous masking procedure.A comparison between the loudness of a primary tone, as evidenced by the magnitude of its residual masking pattern, with the results of loudness judgment tests was made. This was done by replacing the physical scales of pressure level and frequency by the subjective scales of loudness and position. A reasonably good check of computed and measured loudness values was obtained. Patterns for a 1000‐cycle tone were measured to show how the loudness of the standard reference tone is distributed and how this distribution changes as the level of the tone is increased.

ISSN:0001-4966    

DOI:10.1121/1.1906586

出版商:Acoustical Society of America    

年代:1950

数据来源: AIP

摘要:

In investigations of binaural hearing in which the interaural phase difference has been studied, either (1) the stimuli have been pure tones, in which case there is just one interaural phase difference, or (2) no attempt has been made to vary separately the several or many phase differences that exist, one for each frequency component, when both ears are stimulated by complex waves. In the present observations, we have studied the effect of varying the interaural phase relations in the simplest of complex waves: two superposed sinusoids of equal amplitudes. A two‐component tone was presented binaurally, and the interaural phase differenceof one of the componentswas switched alternately from 0 to 180 degrees. The effect of the phase reversal upon the listener's subjective experience and the frequency dependence of the effect are described.

ISSN:0001-4966    

DOI:10.1121/1.1906587

出版商:Acoustical Society of America    

年代:1950

数据来源: AIP

摘要:

The binaural masked threshold for speech depends upon the relation between the interaural phase angles of the speech and those of the noise. When these phase angles are the same, the threshold is high, and both speech and noise appear to be in the same place. When the interaural phase angle of the speech is reversed relative to that of the noise, the threshold is low and the speech and noise appear to be in different places. These relations have been clearly demonstrated with earphones, and they suggest that in free‐field listening the threshold of intelligibility might be affected by the relative locations of the sources of speech and of masking noise. It was found that when the azimuths of the sources of speech and of noise are changed relative to each other, the threshold of intelligibility changes by small but consistent amounts. When the sources are close together, the threshold is high; when the sources are far apart, the threshold is reduced.Although this relation is partially confounded by the effect of azimuth on the sound pressure levels at the ears, the factor of localization appears to play a significant role, especially when two ears are used and when the head is allowed to move. In order that the hard‐of‐hearing may take advantage of these effects, they must have a hearing aid with two separate microphones mounted near the ears and connected each to a separate earphone.

ISSN:0001-4966    

DOI:10.1121/1.1906588

出版商:Acoustical Society of America    

年代:1950

数据来源: AIP

摘要:

In the recent past a program was initiated to survey vehicle, traffic, and industrial noise in the Chicago area. The phase on noise of vehicles has been completed. The investigation included street, elevated, and subway cars; diesel, steam, and electric trains; and motor buses, trucks, and automobiles.Measurements were made of over‐all and octave band levels. Inside of the vehicles, flat network over‐all levels ranged from 85 db in a new “L” car to 95 db in subway cars. The readings in the 400–800 c.p.s. band ranged from 68 db in an automobile to 91 db in subway cars. Outside of and close to vehicles, the flat network over‐all levels ranged from 78 db for automobiles to 94 db for subway trains. Observations in the 400–800 c.p.s. band ranged from 66 db for automobiles to 87 db for subway trains.Variations in the over‐all levels inside of vehicles ranged from ±1 to ±5 db. Variations the 400–800 c.p.s. band ranged from ±2 to ±5 db. Outside of the vehicles, variations ranged from ±2 to ±6 db in both the over‐all and 400–800 c.p.s. band levels.

ISSN:0001-4966    

DOI:10.1121/1.1906589

出版商:Acoustical Society of America    

年代:1950

数据来源: AIP

摘要:

Direct‐radiator loudspeakers are often mounted with the back of the diaphragm working into a completely enclosed space. Conventional theory states that when the maximum linear dimension of such an enclosure is small compared with the wave‐length, the pressure is uniform throughout, and the acoustical impedance presented to the loudspeaker is ‐j/ω(V/ρc2), whereVis the enclosed volume. Although it has not been clearly established how small an enclosure must be before it is “small compared with the wave‐length,” the foregoing expression is generally used, at low audiofrequencies, to calculate the acoustical impedance of closed loudspeaker housings.It is shown here that while the acoustical impedance of a closed rectangular housing is capacitive at very low frequencies, it passes through zero as the frequency increases and becomes that of an inertance as the frequency of the first normal mode is approached. For a typical housing 11 in. × 22 in. × 22 in., the frequency at which the impedance presented to a very small speaker passes through zero is in the vicinity of 70 c.p.s.; at this frequency, the maximum linear dimension of the enclosure is less than one‐seventh of the wave‐length.These results are obtained by using the methods given by Morse for determining the pressure distribution in a room. A point‐source loudspeaker is assumed and the pressure at the source is calculated as the summation of the pressures due to the normal modes of the enclosure, losses being neglected. Measurements of the pressure within the enclosure support this analysis.From measurements of the pressure distribution over the surface of the loudspeaker diaphragm, it may be deduced that the magnitude of the acoustical impedance which the enclosure presents to the loudspeaker diaphragm and the frequency at which the impedance becomes zero depend upon the dimensions of the loudspeaker diaphragm as well as the dimensions of the enclosure.

ISSN:0001-4966    

DOI:10.1121/1.1906590

出版商:Acoustical Society of America    

年代:1950

数据来源: AIP

摘要:

In his theory of streaming caused by sound waves, Eckart shows that time independent streams necessarily follow as part of the solution of the complete wave equatoin, taking into account viscosity and second‐order terms. His treatment is mainly valid for liquids and it proves that the driving force of the streams is proportional to frequency squared. The effect, therefore, is especially important in the ultrasonic region (crystal winds). However, he suggests that slow streams might also be carried in air at audio frequencies.Studies of acoustical streaming phenomena around orifices have been made by the use of smoke particles in a 3‐in. diameter circular tube. These studies covered a range of orifices from thicknesses of 0.5 mm to 19 mm and diameters of 3.5 mm to 20 mm. The frequency lay between 150 to 1000 c.p.s. Velocities in the orifice cover the range of 0 to 700 cm/sec.Close studies of the flow patterns have disclosed that there exist four definite regions of flow as the particle velocity in the orifice is increased. These regions have been represented by “phase diagrams.” Photographs of the various flow patterns in each region of the “phase diagram” have been taken for a number of orifices. Under each observed condition, the acoustic impedance of the orifice is determined by a conventional standing‐wave measurement in the tube.It is shown that the nonlinear properties of the acoustic impedance of an orifice is closely connected with the circulation effects. Quantitative check in one of the circulation regions and a good qualitative over‐all agreement indicate that the nonlinear properties of the impedance is due to the interaction between the sound field and the circulatory effects.

ISSN:0001-4966    

DOI:10.1121/1.1906591

出版商:Acoustical Society of America    

年代:1950

数据来源: AIP