摘要:

A widely used experimental version of the acoustic monopole consists of an acoustic drive of restricted opening forced by a discrete frequency oscillator. To investigate the effects of forward motion on this source, it was mounted above an automobile and driven over an asphalt surface at constant speed past a microphone. The received signal was compared to results computed from an analysis of a fluctuating‐mass‐type point source moving above a finite impedance reflecting plane. Good agreement was found between experiment and theory when a complex normal impedance representative of a fairly hard acoustic surface was used in the analysis. Nonuniform motion of the source was also considered by analyzing the monopole moving with constant acceleration in free space. Computation of the observed signal indicates teat deviations from the constant velocity case become noticeable only at rather large values of acceleration.

ISSN:0001-4966    

DOI:10.1121/1.2003042

出版商:Acoustical Society of America    

年代:1976

数据来源: AIP

摘要:

The reciprocity principle defines a general relationship between transmission and reception in an acoustical system. By applying this principle, the transformation of sound pressure level from a diffuse sound field to the eardrum can be expressed in terms of the frequency. the radiation impedanceZradof the external ear looking outward from the eardrum position, and the load impedanceZdpresented by the eardrum. The formula, which contains no assignable constants, has been used to calculate the diffuse field response curve for a physical model of the external ear combined with an eardrum impedance simulator. An impedance tube was used to measureZradandZd. The magnitude of the response and the frequencies of the resonance peaks are in excellent agreement with other measurements. The diffuse field pressure gain at the primary resonance frequency (2.7 kHz) is approximately 18 dB.

ISSN:0001-4966    

DOI:10.1121/1.2003044

出版商:Acoustical Society of America    

年代:1976

数据来源: AIP

摘要:

Tone‐on‐tone masking patterns from simultaneous and forward masking paradigms are dramatically different. It has been suggested that some of this difference is an effect of suppression, presumably present only in the simultaneous‐masking data. To study this. suggestion psychophysical tuning curves were measured using simultaneous and forward‐masking techniques and measures of suppression were obtained from the same subjects using Houtgast's two‐component forward‐masking paradigm. Both normal and hearing‐impaired listeners were tested. With normal listeners, simultaneous and forward‐masked tuning curves were different in the frequency regions where suppression was most evident. Similar results were obtained from hearing‐impaired listeners in regions of normal sensitivity. However, in regions of decreased sensitivity, simultaneous and forward‐masking tuning curves were the same and no suppression was evident. These results suggest that much of the difference between simultaneous and forward‐masking data is a result of suppression. [Work supported in part by NIH Grant NS12045.]

ISSN:0001-4966    

DOI:10.1121/1.2003055

出版商:Acoustical Society of America    

年代:1976

数据来源: AIP

摘要:

An experimental model for controlled studies of an acoustic neurinoma will be described. The model employs nonhuman primates. It permits chronic experimentation. It is reversible. Essentially, the preparation is based upon the implantation of an inflatable Silastic rubber balloon in the VII and VIII cranial nerves in the internal auditory meatus of the monkey. Prior to and following such preparation, a systematic study of the contralaterally evoked stapedius reflex was performed. Afferent and efferent limbs of the reflex arc were studied. The effects of balloon inflation and deflation were examined. Variables studied included threshold across frequency, dynamic range, habituation, rate of rise, and recovery time. Normative data indicate the characteristics of the monkey stapedius reflex are comparable to man. Implantation reversibly affected all variables except habituation which was permanently affected. Changes in all variables were reversibly influenced by balloon inflation and deflation. The time course and quantitative changes observed will be described. Clinical implications and possible basic mechanisms underlying the effects of the acoustic neurinoma on auditory function will be discussed. [Work supported by NS08181 and RR00166.]

ISSN:0001-4966    

DOI:10.1121/1.2003060

出版商:Acoustical Society of America    

年代:1976

数据来源: AIP

摘要:

A series of measurements were performed to compare the performance of handsets and supra‐aural and ear‐insert‐type headsets on standard and modified couplers, and on the KEMAR ear simulator. These measurements have yielded data enabling comparisons to be made of the frequency response of earphones referred to the same location in the ear, at the eardrum, The effects of ear canal resonances on the upper frequencies, as well as the effect of the imperfect seal that the earphone makes with the ear on the receiver's low‐frequency response, are thus evidenced. One of the measured effects of the imperfect seal is a reduced low frequency response. The other measure of effect is leakage of room noise into the ear covered by the headphone. These effects are related to a lowering of speech transmission quality ratings as the room noise is increased, where headset types are differentially affected. Finally, data will be presented on the equivalent free‐field SPL's to SPL's measured at the eardrum for the various headset types.

ISSN:0001-4966    

DOI:10.1121/1.2003063

出版商:Acoustical Society of America    

年代:1976

数据来源: AIP

摘要:

We developed a vibration pick‐up‐type ear microphone which was formerly reported at the 90th ASA Meeting. After evaluating its function and comparing it with other conventional microphones, we concluded as follows; It is possible to obtain remarkable sensibility without closing the ear canal and to obtain high intelligibility voice in level over 95% of sound articulation. There was no significant difference between voice intelligibility with a mask and that without a mask. Sound articulation in high ambient noise of the vibration pick‐up type ear microphone (110 dB—96%, 125 dB—84%) is much higher than that of noise cancelling microphone (110 dB—87%, 125 dB—77%) and sound pressure type ear microphoen with ear muff (110 dB—85%, 125 dB—68%). By use of the earphone‐microphone, we can simultaneously talk and hear through the ear, thanks to no necessity of obstruction of the ear canal. Applications of the vibration pick‐up type ear microphone are (1) howlingless microphone, (2) free hand microphone, (3) mask microphone, and (4) microphone for voice communication in high ambient noise. We have made communication systems with the vibration pick‐up‐type ear microphone and evaluated in various environments.

ISSN:0001-4966    

DOI:10.1121/1.2003065

出版商:Acoustical Society of America    

年代:1976

数据来源: AIP

摘要:

We present a new coefficient‐coding method of linear predictive coding (LPC) of speech. It employs piecewise linear quantization and requires statistical properties of the LPC reflection coefficient {ki}. In coding the coefficients we first construct histograms of the distribution of each coefficient values obtained from analysis of many different speakers. Then, rather than making quantization levels uniform throughout the range of coefficient values, we divide the range of each coefficient or its transformed version into three regions and assign a different number of quantization levels to each region. Before the range of each coefficient is divided, the minimum valueR0and the maximum valueR3of eachkiare set on the basis of experimental observations. Division of each range into three regions is made by specifyingR1andR2according to the distribution of coefficient values and desired quantization accuracy in each region. Although the piecewise linear coding places its importance on the density of frequencies of the coefficient values, it does not neglect the importance of the spectral sensitivity aspect. In our informal subjective listening test it was observed that the quality of synthetic speech with the transmission rate of 2.4 kbits/sec coded by piecewise quantization was equivalent to the quality with the rate of 3 kbits/sec coded by linear quantization. The piecewise linear quantization scheme can also be used for the arc sine and log area ratio coding methods that normally employ linear quantization. In this case one can expect approximately the same amount of saving of transmission rate as for the nontransformed reflection coefficients.

ISSN:0001-4966    

DOI:10.1121/1.2003074

出版商:Acoustical Society of America    

年代:1976

数据来源: AIP

摘要:

A synthetic signal was formed by passing a burst of energy through an all‐pole digital filter, and Gaussian noise was added to the output. (This is the model of speech production that best recursive fit (BRF) was designed to analyze.) Both linear predictive coding (LPC) and BRF were used to try to recover the filter parameters; at all significant levels of noise BRF is an order of magnitude more effective than LPC. A similar experiment was done on real speech; both LPC and BRF were done (pitch synchronously) on voiced speech, then noise was added to the speech and LPC and BRF were done again. Recovered pole frequencies and bandwidths vary as noise is added; the expected “error” is less for BRF than for LPC. BRF analysis and resynthesis of speech will be demonstrated by the playing of a short passage.

ISSN:0001-4966    

DOI:10.1121/1.2003075

出版商:Acoustical Society of America    

年代:1976

数据来源: AIP

摘要:

When speech is transmitted in a packet‐switched network the variability in packet delays inherent in such a net tends to produce occasional anomalies or “glitches” in the output speech when packets fail to arrive at the destination in a timely fashion. While the frequency of occurrence of these anomalies can be minimized at the expense of buffering and increased overall speech delay, it is likely that a practical network design would represent a compromise which allowed some degradation of the output speech under worst case load conditions. To provide some basic data on the subjective effects of such anomalies a series of listening and communicability tests has been undertaken using speech in which anomaly effects have been introduced by simulation techniques. Anomalies resulting from packet losses due to delay dispersion as well as variation in average delay are introduced at controlled rates in simulated networks using a variety of speech encoding techniques and packetization strategies. Preliminary test results will be presented and a tape with examples of some anomaly effects will be played. [This work was sponsored by the Defense Communications Agency for the Department of Defense.]

ISSN:0001-4966    

DOI:10.1121/1.2003081

出版商:Acoustical Society of America    

年代:1976

数据来源: AIP

摘要:

Courses in elementary acoustics taught at many universities provide introductions to the following six topics: physical acoustics, environmental acoustics, the physiology of hearing, auditory psychophysics, musical acoustics, and the nature of human speech. Electronic demonstrations can be used to enhance instruction in each of the six areas. For example, the modules of an electronic music synthesizer together with an audio system and conventional electronic instrumentation form a versatile laboratory for experiments in sound. Among the demonstrations which can be done are the following. Wave interference can be demonstrated by extracting the separate signals from a stereo recording of signals A + B and A − B. Tone and noise bursts can be used to find the speed of sound, echo and reverberation times. Filter banks, set according to mean audiometric presbycusis data, can show the effects of aging on the frequency response of human hearing. Gently nonlinear electronic devices aid the recognition of combination tones normally generated by the inner ear. Analog delay lines can create repetition pitch from a source of white noise. Sine wave signals from many oscillators can be summed and varied to study the perception of pitch of an inharmonic tone complex like that of a chime. The phase variation of a single rectangular wave with pseudorandom pulse width modulation simulates chorus effect. Much of the effect of nonlinear mode mixing in conventional musical instruments can be simulated by patched of linear electronic components, transient generators and voltage controlled signal processing modules. Three resonant filters allow the synthesis of vowel sounds. Frequency shifted or ring modulated speech sounds can exhibit the importance of vowel formant transitions. Intelligibility experiments with chopped speech serve as an introduction to redundancy, autocorrelation and information theory. We note that one does not pursue this informal experimenting with signal processing equipment for long before one discovers effects which are hard to understand. Further pursuit can lead to new results. For example, our intelligibility experiments with chopped speech suggest that redundancy, measured in spoken English text agrees with that found by Shannon for written text.

ISSN:0001-4966    

DOI:10.1121/1.2003093

出版商:Acoustical Society of America    

年代:1976

数据来源: AIP