Increase In Sound Level Research Articles

Physiological responses to the pulsation threshold paradigm. I: Pulsation threshold patterns do not reproduce physiological rate profiles of high-pass and low-pass noise maskers.

This article compares psychophysical measures of human processing of acoustic stimuli with one neurophysiological representation (normalized discharge rate profiles) of those stimuli. Psychophysical pulsation threshold patterns (PTPs) were derived for high-pass and low-pass noise maskers. Spectral features of both maskers are clearly evident in the PTPs. However, while the representation of high-pass noise in the PTPs becomes sharper with increasing masker level, the representation of low-pass noise degenerates as masker level is increased. One assumption that has been used previously to interpret pulsation threshold data is that PTPs reflect the profile of activity in primary neural elements in response to the masking stimulus. To investigate this hypothesis, normalized-rate profiles of responses to both maskers were derived from populations of auditory-nerve fibers in cats. Normalized-rate profiles do not exhibit the same behavior as PTPs for high-pass noise maskers in that the neural representation of the band edge degenerates as sound level increases. Furthermore, the distinction between the passband and the stop band is lost in the neural rate profiles, whereas the distinction improves in the high-pass noise PTPs.

Sensitivity to amplitude modulated sounds in the anuran auditory nervous system

Auditory responses were recorded from single units in the eighth nerve and in the midbrain torus semicircularis of the leopard frog (Rana pipiens). Acoustic stimuli included sinusoidally amplitude-modulated (AM) tones and noise, as well as pure tones. Mean spike rates were measured at various rates of AM, and the degree to which a unit's spikes were restricted to a particular phase of the modulation cycle was described by a synchronization coefficient. The firing rate of eighth-nerve fibers was largely independent of the rate of AM over the modulation range 10 to 150 Hz. Further, the general shape of the spike rate vs. AM-rate function was invariant with either depth of modulation or sound-pressure level (SPL). Although virtually all eighth-nerve fibers exhibited significant synchronization to the envelope of AM, the shape of the synchronization function depended on the unit's best-excitatory frequency (BEF). Fibers with highest BEF's, presumed to innervate the basilar papilla, generally showed greater synchronization as the AM rate was increased (up to 100-150 Hz). Fibers tuned to the low-and midfrequency region, which innervate the amphibian papilla, exhibited low-pass synchronization characteristics. As the depth of modulation was reduced, the degree of synchronization of eighth-nerve fibers decreased. For a given depth of modulation an increase in sound level tended to decrease the degree of synchronization, but significant synchronization could still be observed at stimulus intensities at least 65 dB above threshold. On the basis of the spike rate vs. AM-rate functions, the temporal selectivity of single cells in the torus could be characterized by five response types: AM nonselective (spike rate was largely independent of the AM rate); AM high-pass (activity increased as the AM rate was increased); AM low-pass (response was greatest for slow AM rates and decreased at high rates); AM band-suppression (these neurons responded well to low and high AM rates, but responded weakly to intermediate rates); and AM-tuned (spike rate was greatest over a narrow range of modulation rates). In these measurements the depth of modulation was held constant at 100%. The five response categories are not discrete, but rather reflect representative examples along a continuum with regard to temporal selectivity. The temporal selectivity exhibited by toral units in their firing rates was not evident in their AM-synchronization functions.(ABSTRACT TRUNCATED AT 400 WORDS)

Electroacoustic assistance of parish church organ music

When the new organist at St. George's‐by‐the‐River church in Rumson, New Jersey complained that his greatest efforts at filling the church with music seemed futile because the reverberation time was too low, we attempted to quantify this feeling and explore low‐cost remedies. The church is of modest size, a 8.1×9.6‐m chancel area and a 19.7×17.8‐m nave. We measured an average reverberation time near 1.5 s (measured in third octave bands up to 8 kHz), observed inefficient coupling of sound energy from the pipe organ chamber via the chancel to the congregation, due to location of the sole acoustic feed high in the side wall of the chancel. To augment the acoustic coupling a microphone was positioned in front of the organ chamber, and the signal was digitally delayed by 82 ms, amplified, and fed into a pair of powerful loudspeakers positioned high and against the rear corners of the nave. This produced a substantial increase in sound level (>6 dB over 3 octaves). Both we and the organist found the natural character of the pipe organ with this mild electroacoustic assist quite gratifying.

Effects of nonlinearities on speech encoding in the auditory nerve

The representation of steady-state vowels in terms of both average rate and temporal aspects of the discharge patterns of populations of auditory-nerve fibers is discussed. The effects of auditory-nerve nonlinearities on this representation is emphasized. Aspects of two rate-related nonlinearities, rate saturation and two-tone suppression, are reviewed. At low sound levels, profiles of discharge rate versus characteristic frequency in populations of auditory-nerve fibers show well-defined peaks at frequencies corresponding to the formants of a vowel stimulus. At levels above about 60 dB SPL, these peaks are not seen because of a combination of rate saturation and two-tone suppression. Units with spontaneous rates less than 1/s show the effects of suppression more dramatically than do units with higher spontaneous rates; nonetheless, this population can retain formant peaks in its rate profiles up to levels at least 20 dB higher than does the higher spontaneous rate population. Aspects of phase-locking to tones and two-tone combinations, including synchrony suppression, are reviewed. Temporal patterns of responses to vowels are analyzed in terms of interval histograms. This analysis shows that in general, phase-locking to the formant frequencies is stronger than locking to other harmonics of the stimulus. As sound level increases, synchrony to the formant frequencies saturates. However, responses to nonformant harmonics are suppressed by responses to the formant harmonics. This synchrony suppression allows the phase-locking to the formant frequencies to remain dominant even at high levels. The exception to this behavior is locking to harmonics and intermodulation products of the first two formant frequencies (2F1, 3F1, F2-F1, etc.) which increases rapidly in amplitude at higher sound levels. These distortion products are, to some extent, a consequence of the rectification inherent in hair cell/nerve fiber transduction and may also reflect the presence of propagating combination tones.

Effects of nonlinearities on speech encoding in the auditory nerve

In this paper we will consider some effects of auditory-nerve nonlinearities on the representation of complex stimuli such as vowels. At low sound levels, profiles of discharge rate versus characteristic frequency in populations of auditory-nerve fibers show well-defined peaks at frequencies corresponding to the formants of a vowel stimulus. At levels above about 60 dB SPL, these peaks are not seen, primarily because of effects of rate saturation. In addition, effects related to two-tone suppression act strongly on units with characteristic frequencies in the vicinity of the second and third formants, suppressing their responses at high levels and contributing to the loss of distinct peaks in this region. Units with spontaneous rates less than about 1/s show the effects of suppression more dramatically than do higher spontaneous units; despite the suppression, however, this population retains formant peaks in its rate profiles up to levels at least 20 dB higher than does the higher spontaneous rate population. The temporal patterns of response of auditory-nerve fibers contain considerable information about the spectrum of a steady state vowel. In general, phaselocking to the formant frequencies is stronger than locking to other harmonics of the stimulus. As sound level increases, synchrony to the formant frequencies saturates. However, responses to nonformant harmonics are suppressed by responses to the formant harmonics. This synchrony suppression allows the phaselocking to the formant frequencies to remain dominant even at high levels. The exception to this behavior is locking to harmonics and intermodulation products of the first two formant frequencies (2F1, 3F1, F2−F1, etc.) which increases rapidly in amplitude at higher sound levels. These distortion products are, to some extent, a consequence of the rectification inherent in hair cell/nerve fiber transduction and may also reflect the presence of propagating combination tones. [Supported by grants from the National Institute of Neurological and Communicative Disorders and Stroke.]

Sound propagation in industrial spaces

Sound fields in industrial halls and open plants have been investigated. Point sources are considered to contribute via direct sound. specularly reflected sound. and diffusely reflected or scattered sound. The diffuse sound field is calculated from solutions of the differential equation describing diffusion processes in homogeneous media filled with absorptive scatterers. Simplified approximations are found from a combination of the farfield solution of diffusion processes and the direct field. From consideration of boundary conditions at reflecting and absorbing planes, complete descriptions are derived for the sound propagation in shallow halls with different acoustical treatment of the ceiling. The theoretical results are consistent with data obtained from model studies and field investigations of industrial halls. Relative to free‐field conditions an increase in sound level is observed due to scattering and specular reflection at distances up to a few free path lengths from the source. At larger dista...

Sound level increase close to enclosure' boundaries

The increase of the average of the potential sound energy density close to enclosure's boundaries (and the corresponding sound level) is theoretically studied, showing that in the corners this value is greater than the 9 dB commonly accepted one. This is due to the presence of interference terms. The study was made on the basis of the eigenmode model applied to a room with hard walls, which allows for stationary waves, in which we suppose a sound diffuse field, and a range of frequencies as large as to excite the normal frequencies of the room and consider them as independent. Finally, the work shows explicitly the expressions for the oblique, the tangential, and the axial modes.

Nonlinear Interaction of Sound with a Resonator in a Duct

An acoustic resonator with a resistive load is attached to a side wall of a duct and is excited by a sound wave. For wavelengths greater than the maximum dimension of the duct cross section, the plane-wave treatment is employed to calculate the absorbed, transmitted, and reflected fractions of the incident power. The results are subsequently compared to experimental findings. It is found that as the sound level increases, the absorbed and reflected fractional powers decrease while the transmitted power increases. [This work was supported by Grant Agreement DOT-OS-30011 with the U. S. Department of Transportation.]

Testing for "recruitment" by electrocochleography. Preliminary results.

Normal electrocochleographic (E.Co.G.) tracings were compared with those showing characteristics which resemble audiometric recruitment. The normal E.Co.G. shows two major features as click levels are raised: 1) Over the intensity range from 0–80 dB H.L., for the click, the VIII nerve action potential (AP) latency decreases from approximately 4 to 1.5 msec; and 2) at low click levels, the AP wave-form is diphasic, and shows a slow growth with increasing intensity, while at higher levels, the AP wave-form is monophasic and increases more rapidly with increases in sound level. Yoshie has referred to the low and high intensity portions of the AP amplitude curve as the L and H curves, respectively. In patients showing the “recruiting responses”, the threshold for the click is elevated and the latency is reduced at threshold. The wave-form of AP is diphasic over the entire intensity range, and AP amplitude grows much more rapidly than in the normal case. It appears that these “recruiting” responses represent the H curve of Yoshie with the L curve removed. The differences between normal and “recruiting” E.Co.G. responses can be given a tentative interpretation based on current findings on the structure and function of the peripheral auditory receptor.

Regulation of middle ear sound transmission in the nonanesthetized rabbit.

AbstractThe regulation of sound transmission through the middle ear of nonanesthetized rabbits was quantitatively investigated by comparing the excitation of the cochlea before and after surgical inactivation of m. stapedius and/or m. tensor tympani in the stimulated ear. The crossed middle ear reflex was used as a measure of the excitation of the cochlea to stimulation with pure tones in the range from 0.5 to 8.0 kHz at intensities up to 125 dB SPL. Sounds through this frequency range were attenuated above a level of 90 to 100 dB SPL. Low frequency tones (0.5 kHz) were attenuated by all levels of activity in the m. stapedius and m. tensor tympani. High frequencies were attenuated only by m. stapedius activity at high intensity levels above reflex threshold (20–30 dB). The m. tensor tympani had no influence on high frequencies, above 2.0 kHz. Improved sound transmission due to reflex activity was not regularly found. The efficiency of the regulation was regarded as high: a 1.0 dB increase in sound level in the ear canal gave only a 0.3 dB increase in the excitation of the cochlea (i.e. the regulating efficiency of the closed‐loop system was 0.7 dB attenuation per 1.0 dB increase in stimulus sound intensity). The regulating efficiency of the open‐loop system was about 2 dB/dB. The open‐loop gain was estimated to 4 during steady‐state. The oscillations in the middle ear reflex response were found to be generated in the m. stapedius feed‐back loop regulating the sound transmission through the middle ear. It was concluded that the function of the acoustic middle ear reflexes can be described as extending the dynamic range of the cochlea and adaptation and it may also be compared with the effect of lateral inhibition.

Measurement of Acoustic Resistance at Sound-Pressure Levels to 171 dB

Absorbing liners, consisting of arrays of acoustic resonators, are being used successfully to suppress combustion instability in rocket and air-breathing engines. For the design of acoustic liners, information is needed on the variation of acoustic resistance with sound pressure at levels above the linear regime, i.e., approximately 100 dB (re 0.0002 μbar). In the work reported herein, a standard impedance tube driven by a high-intensity sound generator was used, along with an improved data-recording technique, to measure the resistance of Helmholtz-type resonator arrays. Incident sound-pressure levels of 171 dB were obtained, which represents an 11-dB increase in sound level over that reported by another investigator in an earlier, similar experiment. A simple correlation of the nonlinear resistance effects with sound pressure is presented.

Critical Review of Sound-System Design Concepts, Applied to “Difficult” Reinforcement Situations

In addition to fulfilling the traditional objectives in the performance of sound-amplification systems, which include the increase of sound level or the improvement of sound coverage throughout the audience areas, sound systems can also be considered devices aimed at increasing the early-to-reverberant energy ratio. (T. J. Schultz, “Acoustics of the Concert Hall,” IEEE Spectrum 56–57 (June 1965).) This approach seems to be particularly important in large multi-purpose halls with long reverberation characteristics, when used for drama. Not only are directional loudspeaker systems needed in such halls to preserve a high ratio of direct to reverberant energy, but equally strict requirements should be set for an acoustically “dry” microphone pickup. This unfortunately is difficult to achieve, since the occasion usually calls for inconspicuous reinforcement with microphones hidden at remote locations. The analysis of the microphone setup for adequate coverage of a theatrical stage leads one to conclude that the development of a new type of wireless personal microphone could ease the situation considerably.

Noise Surveys of Cocktail Parties

This paper discusses and enlarges on a recent theoretical paper by W.R. MacLean on the acoustics of cocktail parties. The discussion is supported by experimental evidence accumulated during the past two years. MacLean's analysis suggests that there is a critical density of participants above which a “quiet” cocktail party becomes abruptly “noisy.” It would appear that one might actually plan a quiet or noisy party as required (assuming control over the number of participants). Unfortunately the cases studied experimentally do not show this quiet-noisy transition, and it is believed that factors not considered in the theory result in a blurring of the distinction. Indications are that there is a gradual increase in sound level to a saturation value that is independent of the properties of the room, the beverages served, and the number of participants. There is, however, dependence on the sex of the participants.

Noise Surveys of Cocktail Parties

This paper discusses and enlarges on a recent theoretical paper by W. R. MacLean on the acoustics of cocktail parties. The discussion is supported by experimental evidence accumulated during the past two years. MacLean's analysis suggests that there is a critical density of participants above which a “quiet” cocktail party becomes abruptly “noisy.” It would appear that one might actually plan a quiet or noisy party as required (assuming control over the number of participants). Unfortunately the cases studied experimentally do not show this quiet-noisy transition, and it is believed that factors not considered in the theory result in a blurring of the distinction. Indications are that there is a gradual increase in sound level to a saturation value that is independent of the properties of the room, of the beverages served, and of the number of participants. There is, however, dependence on the sex of the participants.