Frequency glides in the impulse responses of auditory-nerve fibers

Previous reports of frequency modulations, or glides, in the impulse responses of the auditory periphery have been limited to analyses of basilar-membrane measurements and responses of auditory-nerve (AN) fibers with best frequencies (BFs) greater than 1.7 kHz. These glides increased in frequency as a function of time. In this study, the instantaneous frequency as a function of time was measured for impulse responses of AN fibers in the cat with a range of BFs (250-4500 Hz). Impulse responses were estimated from responses to wideband noise using the reverse-correlation technique. The impulse responses had increasing frequency glides for fibers with BFs greater than 1500 Hz, nearly constant frequency as a function of time of BFs between 750 and 1500 Hz, and decreasing frequency glides for BFs below 750 Hz. Over the levels tested, the glides for fibers at all BFs were nearly independent of stimulus level, consistent with previous reports of impulse responses of the basilar membrane and AN fibers. Implications of the different glide directions observed for different BFs are discussed, specifically in relation to models for the auditory periphery as well as for the derivation of impulse responses for the human auditory periphery based on psychophysical measurements.     

Time-frequency analysis of auditory-nerve-fiber and basilar-membrane click responses reveal glide irregularities and non-characteristic-frequency skirts

Although many properties of click responses can be accounted for by a single, frequency-dispersive traveling wave exciting a single, characteristic-frequency (CF) resonance, some properties, such as waxing and waning cannot. Joint time-frequency distributions (TFDs) were used to help understand click responses of cat single auditory-nerve (AN) fibers (CFs<4 kHz) and published measurements of chinchilla basilar-membrane (BM) motion. For CFs> 800 Hz, the peak energy of the response decreased in latency and frequency as the level increased, as expected. However, at high levels the trend reversed for AN, but not BM, responses. Normalized TFDs, which show the frequency with the peak energy at each response time, revealed glides, as previously reported. Classical theory predicts smooth, upward glides. Instead, at low CFs there were downward glides, and at other CFs glides had substantial irregularities. Finally, click skirts, defined as the longest-latency part of click responses, sometimes showed deviations from CF for above-threshold sound levels. Most of these phenomena are not explained by a single, frequency-dispersive traveling wave exciting a single CF resonance, but they can be accounted for by the interaction of two (or more) excitation drives with different latencies and frequency contents.     

Discrimination of rising and falling simulated single-formant frequency transitions: practice and transition duration effects

Two experiments evaluated discrimination of simulated single-format frequency transitions. In the first experiment, listeners received practice with trial-by-trial feedback in discriminating either rising or falling frequency transitions of three different durations (30, 60, and 120 ms). Transitions either occurred in isolation or were followed by a steady-state sound matched in frequency to the transition end point. Some improvement in discrimination over practice runs occurred for the shortest transitions. Whether performance was evaluated at the beginning or end of practice, there were no differences attributable to transition direction or to whether transitions were followed by steady-state sound. Discrimination, however, was significantly better for the longest transitions. Just noticeable differences (jnd's) for the longest transitions, measured in Hz at transition onsets, were of approximately the same magnitude as jnd's for steady-state sounds that were equal in frequency to the midpoints of the transitions. Subjects of the second experiment discriminated the longer rising and falling transitions, but did not receive extensive practice. Results of experiment 2 replicated results of experiment 1 in showing similar jnd's. Experiment 2 also showed no differences attributable to transition direction or to the presence of the steady-state sound following transitions.     

The effect of temporal asymmetry on amplitude modulation detection using pure-tone carriers (L)

The effect of temporal asymmetry on amplitude modulation detection was studied using sawtooth modulators with rising (ramped) or falling (damped) temporal envelopes within each period of modulation. For pure-tone carriers, damped modulation was more detectable than ramped modulation for a 5-kHz carrier (by a threshold difference of 3.2 dB on average) but not for a 1-kHz carrier. The threshold difference obtained at 5 kHz between the ramped and damped modulators was consistent across modulation rates (8-128 Hz). This carrier frequency dependence suggests that the effect of temporally asymmetry on modulation detection originates from envelope-based, within-channel mechanisms.     

The acoustic features of vervet monkey grunts

East African vervet monkeys give short (125 ms), harsh-sounding grunts to each other in a variety of social situations: when approaching a dominant or subordinate member of their group, when moving into a new area of their range, or upon seeing another group. Although all these vocalizations sound similar to humans, field playback experiments have shown that the monkeys distinguish at least four different calls. Acoustic analysis reveals that grunts have an aperiodic F0, at roughly 240 Hz. Most grunts exhibit a spectral peak close to this irregular F0. Grunts may also contain a second, rising or falling frequency peak, between 550 and 900 Hz. The location and changes in these two frequency peaks are the cues most likely to be used by vervets when distinguishing different grunt types.     

Relationship Between Weight, Speaking Fundamental Frequency, and the Appearance of Phonational Gaps in the Adolescent Male Changing Voice

This 12-month prospective longitudinal study used acoustic analysis to identify phonational gaps in the vocal range of adolescent boys undergoing voice change and to investigate the relationship between the appearance of phonational gaps, weight gain, and changes in speaking fundamental frequency (SF0). Eighteen pubescent boys were recorded producing three descending and three ascending glides over their physiological voice range using the vowel "ah." Recordings were digitized over the range 0-16 kHz and then analyzed to determine both the frequency range and appearance and frequency characteristics of the phonational gaps. Data were plotted against changes in weight and SF0 both as an indicator of pubertal development and to test the hypothesis that changes in weight and SF0 were related to the appearance of phonational gaps. Results indicated that minimum F0 decreased significantly over the time period and phonational gaps increased significantly, but there were no significant changes in maximum F0 or range. Individual data indicated the initial appearance of a lower-frequency gap followed by a higher-frequency gap before the long-term establishment of a midrange gap. At time 5, all boys in the weight range 42.7-44.9 kg had either low- or high-range gaps. The SF0 for this group varied from 117 to 216 Hz. All boys heavier than 54.8 kg had highly variable phonational gaps. SF0 range for this group was 99.5-151 Hz. Transitory low- then high-frequency phonational gaps appeared before the establishment of a midrange phonational gap. In this study, these phonational gaps were associated with certain weight ranges and rapid weight gain, with changes to boys' speaking voices, and with loss of ability to use the mid- and falsetto vocal range.     

Relative weights for frequency glide detection using narrowband noise

Narrowband noise stimuli were used to derive relative weights for detecting frequency glides in a yes/no procedure. One stimulus set was restricted to the duration of the glide. For the second stimulus set, there were fringe noise bands preceding and following the glide. For both sets, the center frequency of the linear glide was either fixed at 1000 Hz or randomly chosen on each trial from the range of 800-1200 Hz. Relative weights as a function of time were derived using a linear model and the linear classification method [A. Ahumada, J. Vis., 2, 121-131 (2002)]. Sensitivity was better for the fixed- than random-frequency conditions, and weight patterns from the random-frequency conditions were less reliable than those obtained from the fixed-frequency conditions. The magnitudes of the relative weights tended to be larger for the second half of the stimulus, suggesting that subjects paid more attention to the later than the earlier parts of stimuli. In the random-frequency conditions, the linear model failed to account for subjects' performance unless the stimuli were expressed in terms of relative changes in frequency rather than absolute frequency.     

Discrimination of frequency transitions by human infants

Difference limens (DLs) for linear frequency transitions using a 1.0-kHz pulsed-tone standard were obtained from 6- to 9-month-old human infants in a series of three experiments. A repeating standard "yes-no" operant headturning technique and an adaptive staircase (tracking) procedure were used to obtain difference limens from a total of 71 infants. The DLs for 300-ms upward and downward linear frequency sweeps were approximately 3%-4% when the repeating standard was an unmodulated 1.0-kHz pulsed tone of 300-ms duration. These DLs for frequency sweeps were not significantly different from DLs for frequency increments and decrements using 330-ms pulsed tones [J. M. Sinnott and R. N. Aslin, J. Acoust. Soc. Am. 78, 1986-1992 (1985)]. The DLs for frequency sweeps of 50 ms appended to the beginning or the end of a 250-ms unmodulated 1.0-kHz tone were approximately 6%-7%. This greater DL for brief frequency sweeps was confirmed by varying the duration but not the extent of the sweep. Finally, DLs were greater than 50% when the repeating standard was a 50-ms rising or falling frequency sweep appended to the beginning of a 250-ms unmodulated 1.0-kHz tone. These results suggest that rapid frequency transitions are much more difficult to discriminate from frequency transitions of the same category (rising or falling) than from either a frequency transition of the opposite category (falling or rising) or an unmodulated tone.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of the salience of pitch and periodicity information on the intelligibility of four-channel vocoded speech: implications for cochlear implants

Recent simulations of continuous interleaved sampling (CIS) cochlear implant speech processors have used acoustic stimulation that provides only weak cues to pitch, periodicity, and aperiodicity, although these are regarded as important perceptual factors of speech. Four-channel vocoders simulating CIS processors have been constructed, in which the salience of speech-derived periodicity and pitch information was manipulated. The highest salience of pitch and periodicity was provided by an explicit encoding, using a pulse carrier following fundamental frequency for voiced speech, and a noise carrier during voiceless speech. Other processors included noise-excited vocoders with envelope cutoff frequencies of 32 and 400 Hz. The use of a pulse carrier following fundamental frequency gave substantially higher performance in identification of frequency glides than did vocoders using envelope-modulated noise carriers. The perception of consonant voicing information was improved by processors that preserved periodicity, and connected discourse tracking rates were slightly faster with noise carriers modulated by envelopes with a cutoff frequency of 400 Hz compared to 32 Hz. However, consonant and vowel identification, sentence intelligibility, and connected discourse tracking rates were generally similar through all of the processors. For these speech tasks, pitch and periodicity beyond the weak information available from 400 Hz envelope-modulated noise did not contribute substantially to performance.     

Novel 53/106 GHz Dual-Band MMW LC Oscillator Implemented in SiGe BiCMOS Technology

In this Paper, we present a fully integrated millimeter wave LC voltage-controlled oscillator (VCO), which employs a novel topology, operating at dual-band frequency of 53.22 GHz-band and 106.44 GHz-band. The low-phase noise performance of –107.3 dBc/Hz and –106.1 dBc/Hz at the offset frequency of 600 kHz, –111.8 dBc/Hz and –110.6 dBc/Hz at the offset frequency of 1 MHz around 53.22 GHz and 106.44 GHz are achieved using IBM BiCMOS-6HP technology, respectively. Two tuning ranges, of 52.7 - 53.8 GHz and 105.4 - 107.6 GHz for the proposed LC VCO are obtained. The output voltage swing of this VCO is around 1.8 V_p-p at the operation frequency of 53.22 GHz and 0.45 V_p-p at 106.44 GHz; the total power consumption is about 16.5 mW. To our knowledge, this is the first oscillator which operates at dual-band frequency above 50 GHz with the best preformance.     

High-synchrony cochlear compound action potentials evoked by rising frequency-swept tone bursts

The auditory compound action potential (CAP) represents synchronous VIIIth nerve activity. Clicks or impulses have been used in the past to produce this synchrony under the assumption that the wide spectral spread inherent in transient signals will activate a large portion of the cochlear partition. However, the observation that only auditory nerve units tuned above 3 kHz contribute to synchronous activity in the N1P1 complex of the CAP [Dolan et al., J. Acoust. Soc. Am. 73, 580-591 (1983)] suggests that temporal delays imposed by the traveling wave result in an asynchronous pattern of VIIIth nerve activation. In order to determine if units tuned below 3 kHz could be recruited into the CAP response, the present study uses tone bursts of exponentially rising frequency to hypothetically activate synchronous discharges of VIIIth nerve fibers along the length of the cochlear partition. The equations defining the frequency sweeps are calculated to be the inverse of the delay-line characteristics of the guinea pig cochlear partition. The resultant sweeps theoretically cause a constant phase displacement of a large portion of the cochlear partition at one time. Compound action potentials recorded in response to the rising frequency sweeps were compared to CAPs evoked by corresponding falling frequency sweeps and clicks. Analysis of the CAP waveforms showed narrower N1 widths and larger N1 and P1 amplitudes for rising sweeps when compared to falling sweeps. This is consistent with the hypothesis of increased synchrony. A further test of the hypothesis was made by using high-pass masking noise to evaluate the contributions of discrete cochlear locations to the CAP ("derived" CAP). Latency functions of the derived CAPs for clicks and falling frequency sweeps showed progressive increases in latency as the cutoff frequency of the high-pass filter was lowered. The latency of the derived CAP for these stimulus conditions reflects traveling wave delays [Aran and Cazals, "Electrocochleography: Animal studies," in Evoked Electrical Activity in The Auditory Nervous System (Academic, New York, 1978)]. In contrast, derived CAPs obtained from rising sweeps showed no change in latency for any cutoff frequencies, indicating a constant delay of response for fibers with different characteristic frequencies (CFs). These results support the theoretical premise underlying the derivation of the rising sweep: Spectral energy with the appropriate temporal organization, dictated by basilar membrane traveling wave properties, will increase CAP synchrony.     

Long-range multi-carrier acoustic communication in deep water using a towed horizontal array

During a recent long-range acoustic communication experiment carried out in deep water, multi-carrier Orthogonal Frequency Division Multiplexing (OFDM) communication signals were transmitted with a 50 Hz bandwidth (225-275 Hz) at various source-receiver ranges from 100 to 700 km. The experiment consisted of two mobile components: (1) a source towed slowly at a speed of 2-3 knots at ～75 m depth and (2) a horizontal line array towed at 3.5 knots at a depth of ～200 m. In addition to beamforming, an interleaver gain is exploited to compensate for low signal-to-noise ratio at the expense of data rate while providing diversity in the frequency domain. Error-free performance is shown at effective data rates of 15 and 7.5 bits/s at ranges of 550 km and 700 km, respectively, by combining interleaved repetitions with low-density parity-check coding after beamforming, demonstrating the feasibility of multi-carrier OFDM communications in deep water using a towed horizontal array.     

Pitch perception of concurrent harmonic tones with overlapping spectra

Fundamental frequency difference limens (F0DLs) were measured for a target harmonic complex tone with nominal fundamental frequency (F0) of 200 Hz, in the presence and absence of a harmonic masker with overlapping spectrum. The F0 of the masker was 0, ± 3, or ± 6 semitones relative to 200 Hz. The stimuli were bandpass filtered into three regions: 0-1000 Hz (low, L), 1600-2400 Hz (medium, M), and 2800-3600 Hz (high, H), and a background noise was used to mask combination tones and to limit the audibility of components falling on the filter skirts. The components of the target or masker started either in cosine or random phase. Generally, the effect of F0 difference between target and masker was small. For the target alone, F0DLs were larger for random than cosine phase for region H. For the target plus masker, F0DLs were larger when the target had random phase than cosine phase for regions M and H. F0DLs increased with increasing center frequency of the bandpass filter. Modeling using excitation patterns and "summary autocorrelation" and "stabilized auditory image" models suggested that use of temporal fine structure information can account for the small F0DLs obtained when harmonics are barely, if at all, resolved.     

Oscillatory rise of bubbles in wormlike micellar fluids with different microstructures

Previous observations of the nontransient oscillations of rising bubbles and falling spheres in wormlike micellar fluids were limited to a single surfactant system. We present an extensive survey of rising bubbles in another system, an aqueous solution of cetylpyridinium chloride and sodium salicylate, with and without NaCl, across a range of concentrations and temperatures. Two different types of oscillations are seen in different concentration ranges, each with its own temperature dependence. Rheological data identify these different hydrodynamic states with different fluid microstructures.     

Discrimination of formant transition onset frequency: psychoacoustic cues at short, moderate, and long durations

Two experiments determined the just noticeable difference (jnd) in onset frequency for speech formant transitions followed by a 1800-Hz steady state. Influences of transition duration (30, 45, 60, and 120 ms), transition-onset region (above or below 1800 Hz), and the rate of transition were examined. An overall improvement in discrimination with duration was observed suggesting better frequency resolution and, consequently, better use of pitch/timbre cues with longer transitions. In addition, falling transitions (with onsets above 1800 Hz) were better discriminated than rising, and changing onset to produce increments in transition rate-of-change in frequency yielded smaller jnd's than changing onset to produce decrements. The shortest transitions displayed additional rate-related effects. This last observation may be due to differences in the degree of dispersion of activity in the cochlea when high-rate transitions are effectively treated as non-time-varying, wideband events. The other results may reflect mechanisms that extract the temporal envelopes of signals: Envelope slope and magnitude differences are proposed to provide discriminative cues that supplement or supplant weaker spectrally based pitch/timbre cues for transitions in the short-to-moderate duration range. It is speculated that these cues may also support some speech perceptual decisions.     

A psychophysical pitch function determined by absolute magnitude estimation and its relation to the musical pitch scale

A psychophysical pitch function, describing the relation of perceived magnitude of pitch to the frequency of a pure tone, was determined by absolute magnitude estimation. Pitch estimates were made by listeners with relative pitch and by absolute pitch possessors for 27 tones spanning a frequency range of 31.5-12,500 Hz in 1/3 octave steps. Results show that the pitch function, plotted in log-log coordinates, is steeper below 200 Hz than at higher frequencies. It is hypothesized that the pitch function's bend may reflect the diversity of neurophysiological mechanisms of pitch encoding in frequency ranges below and above 200 Hz. The variation of the function's slope implies that pitch distances between tones with the same frequency ratios are perceived as larger below 200 Hz than at higher frequencies. It is argued that this implication may apply only to a purely sensory concept of pitch distance and cannot be extended to the perception of musical intervals, a phenomenon governed by musical cognitive principles. The results also show that pitch functions obtained for listeners with relative and absolute pitch have a similar shape, which means that quantitative pitch relations determined for both groups of listeners do not differ appreciably along the frequency scale.     

The pitch of short-duration fundamental frequency glissandos.

Pitch perception for short-duration fundamental frequency (F0) glissandos was studied. In the first part, new measurements using the method of adjustment are reported. Stimuli were F0 glissandos centered at 220 Hz. The parameters under study were: F0 glissando extents (0, 0.8, 1.5, 3, 6, and 12 semitones, i.e., 0, 10.17, 18.74, 38.17, 76.63, and 155.56 Hz), F0 glissando durations (50, 100, 200, and 300 ms), F0 glissando directions (rising or falling), and the extremity of F0 glissandos matched (beginning or end). In the second part, the main results are discussed: (1) perception seems to correspond to an average of the frequencies present in the vicinity of the extremity matched; (2) the higher extremities of the glissando seem more important; (3) adjustments at the end are closer to the extremities than adjustments at the beginning. In the third part, numerical models accounting for the experimental data are proposed: a time-average model and a weighted time-average model. Optimal parameters for these models are derived. The weighted time-average model achieves a 94% accurate prediction rate for the experimental data. The numerical model is successful in predicting the pitch of short-duration F0 glissandos.     

Predicted effects of sensorineural hearing loss on across-fiber envelope coding in the auditory nerve

Cross-channel envelope correlations are hypothesized to influence speech intelligibility, particularly in adverse conditions. Acoustic analyses suggest speech envelope correlations differ for syllabic and phonemic ranges of modulation frequency. The influence of cochlear filtering was examined here by predicting cross-channel envelope correlations in different speech modulation ranges for normal and impaired auditory-nerve (AN) responses. Neural cross-correlation coefficients quantified across-fiber envelope coding in syllabic (0-5 Hz), phonemic (5-64 Hz), and periodicity (64-300 Hz) modulation ranges. Spike trains were generated from a physiologically based AN model. Correlations were also computed using the model with selective hair-cell damage. Neural predictions revealed that envelope cross-correlation decreased with increased characteristic-frequency separation for all modulation ranges (with greater syllabic-envelope correlation than phonemic or periodicity). Syllabic envelope was highly correlated across many spectral channels, whereas phonemic and periodicity envelopes were correlated mainly between adjacent channels. Outer-hair-cell impairment increased the degree of cross-channel correlation for phonemic and periodicity ranges for speech in quiet and in noise, thereby reducing the number of independent neural information channels for envelope coding. In contrast, outer-hair-cell impairment was predicted to decrease cross-channel correlation for syllabic envelopes in noise, which may partially account for the reduced ability of hearing-impaired listeners to segregate speech in complex backgrounds.     

基于FPGA的高速电光选通系统设计

介绍了一种获取高速调制电信号的新方法－基于FPGA的高速电光选通系统.此系统分为选通脉冲和高压调控两个模块.选通脉冲模块由高速信号放大、FPGA延时、可控延迟传输线三个部分组成.利用FPGA高密度、高可靠性、可反复擦写和可以现场编程、灵活调制的特点,将整个系统的主要控制部分集成在FPGA中,并将延时分为数字延时和模拟延时两部分.然后利用FPGA实现数字延时,可控延时线实现模拟延时.经试验检测,高压部分可以产生重复频率1 Hz~1 kHz,步进1 Hz,延时范围为0~1 μs,步进为1 ns,幅度为8 000 V,前沿和后沿小于10 ns,抖动小于1 ns的高压矩形电脉冲,从而满足各种电光调制系统中的需要.     

Auditory brainstem responses with optimized chirp signals compensating basilar-membrane dispersion

This study examines auditory brainstem responses (ABR) elicited by rising frequency chirps. The time course of frequency change for the chirp theoretically produces simultaneous displacement maxima by compensating for travel-time differences along the cochlear partition. This broadband chirp was derived on the basis of a linear cochlea model [de Boer, "Auditory physics. Physical principles in hearing theory I," Phys. Rep. 62, 87-174 (1980)]. Responses elicited by the broadband chirp show a larger wave-V amplitude than do click-evoked responses for most stimulation levels tested. This result is in contrast to the general hypothesis that the ABR is an electrophysiological event most effectively evoked by the onset or offset of an acoustic stimulus, and unaffected by further stimulation. The use of this rising frequency chirp enables the inclusion of activity from lower frequency regions, whereas with a click, synchrony is decreased in accordance with decreasing traveling velocity in the apical region. The use of a temporally reversed (falling) chirp leads to a further decrease in synchrony as reflected in ABR responses that are smaller than those from a click. These results are compatible with earlier experimental results from recordings of compound action potentials (CAP) [Shore and Nuttall, "High synchrony compound action potentials evoked by rising frequency-swept tonebursts," J. Acoust. Soc. Am. 78, 1286-1295 (1985)] reflecting activity at the level of the auditory nerve. Since the ABR components considered here presumably reflect neural response from the brainstem, the effect of an optimized synchronization at the peripheral level can also be observed at the brainstem level. The rising chirp may therefore be of clinical use in assessing the integrity of the entire peripheral organ and not just its basal end.