The effect of loading on disturbance sounds of the Atlantic croaker Micropogonius undulatus: air versus water

Physiological work on fish sound production may require exposure of the swimbladder to air, which will change its loading (radiation mass and resistance) and could affect parameters of emitted sounds. This issue was examined in Atlantic croaker Micropogonius chromis by recording sounds from the same individuals in air and water. Although sonograms appear relatively similar in both cases, pulse duration is longer because of decreased damping, and sharpness of tuning (Q factor) is higher in water. However, pulse repetition rate and dominant frequency are unaffected. With appropriate caution it is suggested that sounds recorded in air can provide a useful tool in understanding the function of various swimbladder adaptations and provide reasonable approximation of natural sounds. Further, they provide an avenue for experimentally manipulating the sonic system, which can reveal details of its function not available from intact fish underwater.     

Roughness of organ pipe sound due to frequency comb

In the sound spectrum of flue organ pipes in addition to the usual harmonic partials, sometimes a series of equidistant but not harmonic lines can be found. This phenomenon has been observed in the recorded sound of pipes from different pipe ranks. The second set of spectral lines is similar to "frequency combs" used in optics for accurate measurement of optical frequencies. Analysis of measured sound spectra with and without frequency comb and simulations are presented and discussed in the paper. The appearance of frequency combs in the sound spectrum is explained by a model that assumes the presence of a mouth tone in addition to the pipe sound. Mouth tone bursts are generated when the oscillating air jet passes the upper lip. The burst repetition frequency is locked to the fundamental frequency of the pipe and the bursts are coherent with a pulse-to-pulse phase shift. The phase shift explains the observed frequency offset of the frequency comb to the harmonic frequencies. The simulations also show that weak and fluctuating mouth tones cannot generate frequency comb due to a lack of coherence.     

Underwater sound pressure variation and bottlenose dolphin (Tursiops truncatus) hearing thresholds in a small pool

Studies of underwater hearing are often hampered by the behavior of sound waves in small experimental tanks. At lower frequencies, tank dimensions are often not sufficient for free field conditions, resulting in large spatial variations of sound pressure. These effects may be mitigated somewhat by increasing the frequency bandwidth of the sound stimulus, so effects of multipath interference average out over many frequencies. In this study, acoustic fields and bottlenose dolphin (Tursiops truncatus) hearing thresholds were compared for pure tone and frequency modulated signals. Experiments were conducted in a vinyl-walled, seawater-filled pool approximately 3.7 x 6 x 1.5 m. Acoustic signals were pure tone and linear and sinusoidal frequency modulated tones with bandwidths/modulation depths of 1%, 2%, 5%, 10%, and 20%. Thirteen center frequencies were tested between 1 and 100 kHz. Acoustic fields were measured (without the dolphin present) at three water depths over a 60 x 65 cm grid with a 5-cm spacing. Hearing thresholds were measured using a behavioral response paradigm and up/down staircase technique. The use of FM signals significantly improved the sound field without substantially affecting the measured hearing thresholds.     

Auditory stream segregation in monkey auditory cortex: effects of frequency separation, presentation rate, and tone duration

Auditory stream segregation refers to the organization of sequential sounds into "perceptual streams" reflecting individual environmental sound sources. In the present study, sequences of alternating high and low tones, "...ABAB...," similar to those used in psychoacoustic experiments on stream segregation, were presented to awake monkeys while neural activity was recorded in primary auditory cortex (A1). Tone frequency separation (AF), tone presentation rate (PR), and tone duration (TD) were systematically varied to examine whether neural responses correlate with effects of these variables on perceptual stream segregation. "A" tones were fixed at the best frequency of the recording site, while "B" tones were displaced in frequency from "A" tones by an amount = delta F. As PR increased, "B" tone responses decreased in amplitude to a greater extent than "A" tone responses, yielding neural response patterns dominated by "A" tone responses occurring at half the alternation rate. Increasing TD facilitated the differential attenuation of "B" tone responses. These findings parallel psychoacoustic data and suggest a physiological model of stream segregation whereby increasing delta F, PR, or TD enhances spatial differentiation of "A" tone and "B" tone responses along the tonotopic map in A1.     

Blue whale (Balaenoptera musculus) sounds from the North Atlantic

Sounds of blue whales were recorded from U.S. Navy hydrophone arrays in the North Atlantic. The most common signals were long, patterned sequences of very-low-frequency sounds in the 15-20 Hz band. Sounds within a sequence were hierarchically organized into phrases consisting of one or two different sound types. Sequences were typically composed of two-part phrases repeated every 73 s: a constant-frequency tonal "A" part lasting approximately 8 s, followed 5 s later by a frequency-modulated "B" part lasting approximately 11 s. A common sequence variant consisted only of repetitions of part A. Sequences were separated by silent periods averaging just over four minutes. Two other sound types are described: a 2-5 s tone at 9 Hz, and a 5-7 s inflected tone that swept up in frequency to ca. 70 Hz and then rapidly down to 25 Hz. The general characteristics of repeated sequences of simple combinations of long-duration, very-low-frequency sound units repeated every 1-2 min are typical of blue whale sounds recorded in other parts of the world. However, the specific frequency, duration, and repetition interval features of these North Atlantic sounds are different than those reported from other regions, lending further support to the notion that geographically separate blue whale populations have distinctive acoustic displays.     

Behavioral avoidance threshold level of a harbor porpoise (Phocoena phocoena) for a continuous 50 kHz pure tone

The use of ultrasonic sounds in alarms for gillnets may be advantageous, but the deterring effects of ultrasound on porpoises are not well understood. Therefore a harbor porpoise in a large floating pen was subjected to a continuous 50 kHz pure tone with a source level of 122+/-3 dB (re 1 microPa, rms). When the test signal was switched on during test periods, the animal moved away from the sound source. Its respiration rate was similar to that during baseline periods, when the sound was switched off. The behavior of the porpoise was related to the sound pressure level distribution in the pen. The sound level at the animal's average swimming location during the test periods was approximately 107+/-3 dB (re 1 microPa, rms). The avoidance threshold sound pressure level for a continuous 50 kHz pure tone for this porpoise, in the context of this study, is estimated to be 108+/-3 dB (re 1 microPa, rms). This study demonstrates that porpoises may be deterred from an area by high frequency sounds that are not typically audible to fish and pinnipeds and would be less likely masked by ambient noise.     

Sounds, source levels, and associated behavior of humpback whales, southeast Alaska

Humpback whales in Southeast Alaskan waters produced five categories of sounds: moans, grunts, pulse trains, blowhole-associated sounds, and surface impacts. Frequencies (Hz) of moans and grunts were 20-1900. Major energy in low-frequency pulse trains was in a band of 25-80 Hz with pulse duration of 300-400 ms. Blowhole-associated sounds, recorded as transiting whales encountered one another, were of two types: shrieks, 555-2000 Hz, and trumpetlike horn blasts with fundamental at 414 Hz (median). Pulses and spread spectrum noise were associated with gas bubble formation and explosive bursts, respectively, in connection with spiral feeding maneuvers. Surface impacts resulted from fluke or flipper slaps in sequences of 3-21 sounds. Source levels ranged from 162 (low-frequency pulse trains) to 192 dB (surface impacts), re: 1 microPa, 1 m. Songs, commonly heard on winter breeding grounds, were absent from our recordings. Feeding and perhaps certain other whale activities can be monitored based on sound production.     

Coding of amplitude-modulated signals in the cochlear nucleus of a grass frog

To study the mechanisms that govern the coding of temporal features of complex sound signals, responses of single neurons located in the dorsal nucleus of the medulla oblongata (the cochlear nucleus) of a curarized grass frog (Rana temporaria) to pure tone bursts and amplitude modulated tone bursts with a modulation frequency of 20 Hz and modulation depths of 10 and 80% were recorded. The carrier frequency was equal to the characteristic frequency of a neuron, the average signal level was 20–30 dB above the threshold, and the signal duration was equal to ten full modulation periods. Of the 133 neurons studied, 129 neurons responded to 80% modulated tone bursts by discharges that were phase-locked with the envelope waveform. At this modulation depth, the best phase locking was observed for neurons with the phasic type of response to tone bursts. For tonic neurons with low characteristic frequencies, along with the reproduction of the modulation, phase locking with the carrier frequency of the signal was observed. At 10% amplitude modulation, phasic neurons usually responded to only the onset of a tone burst. Almost all tonic units showed a tendency to reproduce the envelope, although the efficiency of the reproduction was low, and for half of these neurons, it was below the reliability limit. Some neurons exhibited a more efficient reproduction of the weak modulation. For almost half of the neurons, a reliable improvement was observed in the phase locking of the response during the tone burst presentation (from the first to the tenth modulation period). The cooperative histogram of a set of neurons responding to 10% modulated tone bursts within narrow ranges of frequencies and intensities retains the information on the dynamics of the envelope variation. The data are compared with the results obtained from the study of the responses to similar signals in the acoustic midbrain center of the same object and also with the psychophysical effect of a differential sensitivity increase in the process of adaptation.     

Obtaining calibrated sound pressure levels from consumer digital audio recorders

Audio recording of environmental sound is an increasingly efficient method for autonomously sensing many ecological and anthropogenic processes. The increasing capabilities of consumer digital audio recorders (DARs), especially increases in storage capacity and reductions in power consumption, enable continuous audio recordings exceeding 1 month in duration with packages that are relatively small and inexpensive. To augment the ability of these systems to document the range of sounds present at a location, this paper examines two methods for calibrating recorders to measure sound levels. Compressed audio recorded by a DAR can be processed to yield relatively consistent measures of one-third octave band L_eq values within a limited frequency and dynamic range. This was evaluated by synchronizing data with a Type-1 sound level meter. The calibration is stable over a 23 day deployment outdoors with wide variation in ambient temperature and humidity. When considering aggregate acoustic metrics over time or a wide bandwidth such as an hourly A-weighted L₅₀, the results can be quite accurate (within 1 dBA).     

Intracellular recordings from supporting cells in the guinea-pig cochlea: AC potentials

Supporting cells and hair cells from the low-frequency region of the guinea-pig cochlea were studied in vivo using intracellular recording and horseradish peroxidase marking techniques. Response characteristics of the support cells to tone bursts at various sound levels, frequencies, and durations were compared to hair-cell responses and potentials recorded in the organ of Corti fluid spaces. Findings suggest that the fundamental component of the support-cell response accrues from hair-cell-generated currents. This component of the support-cell response probably results from the flow of receptor currents across support-cell membranes through nonspecialized membrane patches, or across nonspecialized membranes and through gap junctions that couple adjacent support cells. Findings suggest a lack of electrotonic coupling between hair cells and neighboring support cells.     

Enhancing a tone by shifting its frequency or intensity

When a test sound consisting of pure tones with equal intensities is preceded by a precursor sound identical to the test sound except for a reduction in the intensity of one tone, an auditory "enhancement" phenomenon occurs: In the test sound, the tone which was previously softer stands out perceptually. Here, enhancement was investigated using inharmonic sounds made up of five pure tones well resolved in the auditory periphery. It was found that enhancement can be elicited not only by increases in intensity but also by shifts in frequency. In both cases, when the precursor and test sounds are separated by a 500-ms delay, inserting a burst of pink noise during the delay has little effect on enhancement. Presenting the precursor and test sounds to opposite ears rather than to the same ear significantly reduces the enhancement resulting from increases in intensity, but not the enhancement resulting from shifts in frequency. This difference suggests that the mechanisms of enhancement are not identical for the two types of change. For frequency shifts, enhancement may be partly based on the existence of automatic "frequency-shift detectors" [Demany and Ramos, J. Acoust. Soc. Am. 117, 833-841 (2005)].     

Assessment of the change in similarity judgements of auralized engine sounds caused by changes in frequency resolution of transfer functions

Auralization facilitates aural examination of contributions from different sound sources, individually and as parts of a context. Auralizations can be created by filtering sounds of the perceptually most salient sources through binaural transfer functions (BTFs) from source positions to a listening position. When psychoacoustic analysis is based on auralizations, the auralizations need to give the same impression as real sounds. The objective of this study was to determine the frequency resolution required for auralizations to be perceptually equivalent to recordings made with an artificial head. Auralizations of the contribution of engine sounds to interior sounds of a truck were examined. In listening tests auralizations based on simplified BTFs were compared to artificial head recordings. The BTFs were simplified by lowering the frequency resolution and by smoothing in the frequency domain. Auralizations made through BTFs with a resolution of 4 Hz or higher or smoothed with maximum 1/96 octave moving average filters were perceived as similar to artificial head recordings.     

Frequency-dependent changes in absolute hearing threshold caused by perception of a previous sound

This study investigated effects of a previous sound presentation at the absolute threshold of hearing. Changes in threshold were measured when a pure tone at 60 dB SPL preceded a test tone in the contra- or ipsilateral ear. When the previous and test sounds both had the same frequency of 500 Hz, threshold decreased approximately 2 dB in the contralateral ear, and increased slightly in the ipsilateral ear. On the other hand, when the frequency of the previous sound differed from that of the test sound, the threshold was decreased slightly in the ipsilateral ear.     

Effects of mid-frequency active sonar on hearing in fish

Caged fish were exposed to sound from mid-frequency active (MFA) transducers in a 5 × 5 planar array which simulated MFA sounds at received sound pressure levels of 210 dB SPL(re 1 μPa). The exposure sound consisted of a 2 s frequency sweep from 2.8 to 3.8 kHz followed by a 1 s tone at 3.3 kHz. The sound sequence was repeated every 25 s for five repetitions resulting in a cumulative sound exposure level (SEL(cum)) of 220 dB re 1 μPa(2) s. The cumulative exposure level did not affect the hearing sensitivity of rainbow trout, a species whose hearing range is lower than the frequencies in the presented MFA sound. In contrast, one cohort of channel catfish showed a statistically significant temporary threshold shift of 4-6 dB at 2300 Hz, but not at lower tested frequencies, whereas a second cohort showed no change. It is likely that this threshold shift resulted from the frequency spectrum of the MFA sound overlapping with the upper end of the hearing frequency range of the channel catfish. The observed threshold shifts in channel catfish recovered within 24 h. There was no mortality associated with the MFA sound exposure used in this test.     

Sound radiation around a flying fly

Many insects produce sounds during flight. These acoustic emissions result from the oscillation of the wings in air. To date, most studies have measured the frequency characteristics of flight sounds, leaving other acoustic characteristics--and their possible biological functions--unexplored. Here, using close-range acoustic recording, we describe both the directional radiation pattern and the detailed frequency composition of the sound produced by a tethered flying (Lucilia sericata). The flapping wings produce a sound wave consisting of a series of harmonics, the first harmonic occurring around 190 Hz. In the horizontal plane of the fly, the first harmonic shows a dipolelike amplitude distribution whereas the second harmonic shows a monopolelike radiation pattern. The first frequency component is dominant in front of the fly while the second harmonic is dominant at the sides. Sound with a broad frequency content, typical of that produced by wind, is also recorded at the back of the fly. This sound qualifies as pseudo-sound and results from the vortices generated during wing kinematics. Frequency and amplitude features may be used by flies in different behavioral contexts such as sexual communication, competitive communication, or navigation within the environment.     

Sound source localization by the plainfin midshipman fish, Porichthys notatus

The aim of this study was to use plainfin midshipman fish (Porichthys notatus) as a general model to explore how fishes localize an underwater sound source in the relatively simple geometry of a monopole sound field. The robust phonotaxic responses displayed by gravid females toward a monopole sound projector (J-9) broadcasting a low-frequency (90 Hz) tone similar to the fundamental frequency of the male's advertisement call were examined. The projector's sound field was mapped at 5 cm resolution azimuth using an eight-hydrophone array. Acoustic pressure was measured with the array and acoustic particle motion was calculated from pressure gradients between hydrophones. The response pathways of the fish were analyzed from video recordings and compared to the sound field. Gravid females at initial release were directed toward the sound source, and the majority (73%) swam to the playback projector with straight to slightly curved tracks in the direction of the source and in line with local particle motion vectors. In contrast, the initial direction of the control (sound-off) group did not differ from random. This paper reports on a comparison of fish localization behavior with directional cues available in the form of local particle motion vectors.     

Multiple scattering in a reflecting cavity: application to fish counting in a tank.

Classical fisheries acoustics techniques are useless in the presence of multiple scattering or reflecting boundaries. A general technique is developed that provides the number and the scattering strength of scatterers in motion placed inside a highly reflecting cavity. This approach is based on multiple scattering theory. The idea is to measure the average effect of the scatterers on the acoustic echoes of the cavity interfaces. This leads to the measure of the scattering mean free path, a typical length that characterizes the scattering strength of the cloud of scatterers. Numerical results are shown to agree with a simple theoretical analysis. Experiments are performed with fish in a tank at two different scales: ultrasonic frequency (400 kHz) in a 1.4-l beaker with 1-cm-long fish as well as fisheries acoustics frequency (12.8 kHz) in a 30-m3 tank with 35-cm-long fish. These results have interesting applications to fish target strength measurement and fish counting in aquaculture.     

20-Hz pulses and other vocalizations of fin whales, Balaenoptera physalus, in the Gulf of California, Mexico.

Low-frequency vocalizations were recorded from fin whales, Balaenoptera physalus, in the Gulf of California, Mexico, during three cruises. In March 1985, recorded 20-Hz pulses were in sequences of regular 9-s interpulse intervals. In August 1987, nearly all were in sequences of doublets with alternating 5- and 18-s interpulse intervals. No 20-Hz pulse sequences of any kind were detected in February 1987. The typical pulse modulated from 42 to 20 Hz and its median duration was 0.7 s (1985 data). Most other fin whale sounds were also short tonal pulses averaging 82, 56, and 68 Hz, respectively, for the three cruises; 89% were modulated in frequency, mostly downward. Compared to Atlantic and Pacific Ocean regions, Gulf of California 20-Hz pulses were unique in terms of frequency modulation, interpulse sound levels, and temporal patterns. Fin whales in the Gulf may represent a regional stock revealed by their sound characteristics, a phenomenon previously shown for humpback whales, birds, and fish. Regional differences in fin whale sounds were found in comparisons of Atlantic and Pacific locations.     

Audio and sound archives as a resource for voice science: A preliminary review

Archives of voice recordings could provide a source of information for voice scientists and clinicians interested in voice analysis and in cultural and historical changes of vocal styles and qualities. Large collections of sound recordings exist that could be used as databases for such inquiries, although no comprehensive list of such collections currently exists. A preliminary survey of major collections is presented. Voice scientists and voice archivists have many common areas of interest in the recording, reproduction, copying, and analysis of sound. The Recording and Research Center, as part of its ongoing research in establishment of standards for voice analysis, has begun an archive of laboratory recordings. A protocol for recording trained, normal, abnormal, and neurologically impaired voices is in development. This survey of sound archives will continue as well.