Analytic and synthetic pitch of two-tone complexes

An experiment was performed in which subjects had to judge whether the pitch of two sequential sounds went up or down. The sounds were harmonic two-tone complexes. They were constructed in such a way that the frequency of one harmonic remained fixed, the frequency of the other went up or down, and the missing fundamental moved in the opposite direction. Results show that, for partials of low harmonic order, most subjects tend to follow the frequency of the moving partial, whereas for partials of order 6 or higher, responses are divided more or less equally between tracking of the moving partial and tracking of the missing fundamental.     

Pitch identification of simultaneous dichotic two-tone complexes

The optimum processor theory of Goldstein can, in principle, account for pitch perception phenomena involving simultaneous dichotic complex tones. The frequency-coding noise function, which is the only free parameter of the model, was estimated with pitch identification data of two simultaneous two-tone complexes presented to different ears. This "sigma" function was found to have a shape similar to that of the function derived from data on identification performance for single pitches. The sigmas in the simultaneous pitch identification experiment are larger by an amount that differs from subject to subject. By using different methods of data analysis it was found that the pitch estimation processes for the two tones are independent for most subjects. This allows a simple extension of Goldstein's optimum processor theory.     

Pitch identification of simultaneous diotic and dichotic two-tone complexes

This study examines subjects' ability to recognize the pitches of two missing fundamentals in two simultaneous two-tone complexes whose partials are distributed in various ways between subjects' ears. The data show that identification performance is affected on different levels. Limited frequency resolution in the peripheral auditory system can degrade performance, but only if none of the four stimulus partials is aurally resolved. Identification performance is only weakly dependent on the manner of distributing partials between the ears. In some cases it was found that, probably at a very central level (e.g., attention), the identification processes of both simultaneous pitches interfere with one another. Some subjects are more likely to identify the pitch of one two-tone complex when the harmonic order of the other complex is higher than when this harmonic order is lower. Finally, some subjects tend to hear the complex tones analytically, i.e., perceive pitches of single partials instead of the missing fundamentals for some distribution of partials between the ears.     

中国现代二-音钟的振动方式

用全息干涉法对苏州乐器厂制造的扁钟的振动方式进行了研究。发现钟的非圆形状产生了许多成对的方式,其中一对的一个方式的节线在钟的隆起上,另一个方式在那里则是腹线。两个最低方式的频率比值为1.188,接近于小三度(1.189),这部分是由于钟上铸有六条调音槽的结果。     

Effect of signal phase and masker separation on two-tone masking

The detectability of a sinusoid masked by two sinusoids was studied as a function of signal phase and the frequency separation between the two maskers. The signal frequency fs was equal to the arithmetic mean of the two masker frequencies, fl and fh, where fl less than fh. Signal frequencies of 1 and 4 kHz, eight signal phases, and 12 values of r = (fh-fl)/fs from 0.01-1.0 were used. The data could be divided into three regions. For large masker separations, r greater than 0.4, no consistent effects of signal phase were observed. For r less than 0.4, an effect of signal phase was evident at both signal frequencies. However, the effect of signal phase was different for the two regions 0.03 less than r less than 0.4 and r less than 0.03. For moderate masker separations, 0.03 less than r less than 0.4, masked thresholds were lowest at phases of 0 degrees and 180 degrees and highest at phases of 90 degrees and 270 degrees. For small masker separations, r less than 0.03, masked threshold was highest at 0 degree and the effect of signal phase depended on signal frequency. The different form of the phase effect for these three regions is discussed in terms of the use of different cues, arising from temporal resolution, spectral filtering, combination tones, and envelope spectra.     

Auditory two-tone suppression from a subcritical Hopf cochlea

Cochlear two-tone suppression is the dominant contrast-sharpening phenomenon of hearing and provides a decisive test for the correct implementation of hearing nonlinearities in models of the cochlea. Although critically tuned Hopf amplifiers were shown recently to be fruitful models of intricate phenomena in the physiology of the human ear, we find that only a model based on subcritical Hopf amplifiers is capable of reproducing physiologically measured two-tone suppression data adequately. In addition, we provide a detailed explanation of the two-tone suppression phenomenon, including its quantitative characterization.     

Harmonic detection with tunable diode lasers —two-tone modulation

The minimum absorption detectable by a tunable diode laser spectrometer utilising harmonic techniques is often limited by interference fringes generated by scattered light. The sensitivity of the spectrometer to absorption can be increased by applying a jitter modulation. In this paper, the theory of harmonic response for single- and two-tone modulation over optical fringes and Lorentzian absorption lines is developed and compared to experimental measurements. A simple analytic expression for the two-tone harmonic line shape is derived. This expression provides a physical understanding of the effects of the second modulation, and a means to unravel the effects of the second modulation on the linewidth and line shape. For a specific choice of the jitter frequency and phase, it is possible to simultaneously minimise the fringe signal and increase the harmonic absorption signal. The results of this investigation are applicable to trace gas detection using tunable diode lasers, and to other areas of spectroscopy and magnetic resonance where harmonic techniques are used.This work was supported by the Natural Sciences and Engineering Research Council of Canada, and the Ontario Ministry of the Environment     

Electrophysiological evidence of nonlinear distortion products to two-tone stimuli

Spectral analysis of auditory-evoked potential recordings from ten normal-hearing subjects to two-tone signals revealed energy at difference tone (DT = f2-f1) and cubic difference (CDT = 2f1-f2) frequencies that was not present in the acoustic signal. Control experiments and calibrations provided substantial evidence supportive of the biological nature of these auditory nonlinearities, suggesting that they are not the result of electromagnetic, acoustic, or analytic artifact. Amplitudes of DT- and CDT-evoked responses were evaluated for rarefaction and condensation signals with f1 = 510 and 800 Hz across frequency ratios (f2/f1) of 1.16, 1.26, 1.36, and 1.46. Additionally, time-domain summation and subtraction of separately collected evoked responses to rarefaction and condensation signals were performed to demonstrate that these electrophysiological DT and CDT responses reflect their expected quadratic and cubic nature. Suggestions for development of clinical applications of assessing auditory nonlinearities using this methodology are provided.     

Prediction of the two-tone suppression and intermodulation performance of auditory systems

Using a model based on subcritical Hopf amplifiers, closed form expressions are obtained for two-tone suppression and the third-order intermodulation performance of the human auditory system. The proposed model approximates the Hopf amplifier characteristic using Fourier-series expansion. The parameters of the Fourier-series approximation can be easily obtained without recourse to sophisticated curve-fitting techniques. The results are compared with previously reported observations.     

Bandwidth of spectral resolution for two-formant synthetic vowels and two-tone complex signals

Spectral integration refers to the summation of activity beyond the bandwidth of the peripheral auditory filter. Several experimental lines have sought to determine the bandwidth of this "supracritical" band phenomenon. This paper reports on two experiments which tested the limit on spectral integration in the same listeners. Experiment I verified the critical separation of 3.5 bark in two-formant synthetic vowels as advocated by the center-of-gravity (COG) hypothesis. According to the COG effect, two formants are integrated into a single perceived peak if their separation does not exceed approximately 3.5 bark. With several modifications to the methods of a classic COG matching task, the present listeners responded to changes in pitch in two-formant synthetic vowels, not estimating their phonetic quality. By changing the amplitude ratio of the formants, the frequency of the perceived peak was closer to that of the stronger formant. This COG effect disappeared with larger formant separation. In a second experiment, auditory spectral resolution bandwidths were measured for the same listeners using common-envelope, two-tone complex signals. Results showed that the limits of spectral averaging in two-formant vowels and two-tone spectral resolution bandwidth were related for two of the three listeners. The third failed to perform the discrimination task. For the two subjects who completed both tasks, the results suggest that the critical region in vowel task and the complex-tone discriminability estimates are linked to a common mechanism, i.e., to an auditory spectral resolving power. A signal-processing model is proposed to predict the COG effect in two-formant synthetic vowels. The model introduces two modifications to Hermansky's [J. Acoust. Soc. Am. 87, 1738-1752 (1990)] perceptual linear predictive (PLP) model. The model predictions are generally compatible with the present experimental results and with the predictions of several earlier models accounting for the COG effect.     

Musical pitch of two-tone complexes and predictions by modern pitch theories.

Most studies of the musical pitch of harmonic tone complexes have utilized signals comparing two or more successive harmonics. The present study provides systematic data on melodic interval recognition by three musically experienced subjects with sounds whose missing fundamentals were represented by two nonsuccessive harmonics nf0,(n + m)f0, delivered to separate ears. Data were obtained in the ranges 1 less than or equal to n less than or equal to 9, 2 less than or equal to m less than or equal to 4, and 200 Hz less than or equal to f0 less than or equal to 1000 Hz. The data are interpreted in the light of three theories, the "optimum processor theory," the "virtual pitch theory," and the "pattern transformation theory." For each theory, a constraint on preformance is proposed based on interference between the "analytic" and "synthetic" pitch perception modes. The former is obtained with large spacings between harmonics, where listeners are more likely to perceive harmonics as individual tones, each having their own pitch. This degrades the listener's ability to hear the fundamental pitch.     

Experimental studies on sound and vibration of a two-tone Chinese Peace Bell

In order to examine whether the characteristics of the bell are coincident with the design and make some constructive suggestions for the tuning of bell, the frequency characteristics of sound and the vibrational modes of a two-tone Chinese Peace Bell have been studied. With Welch's spectral estimate, the main partials of radiated sound of the bell have been found out. With time-frequency analysis, the changes of the spectrum with time have been shown. By conditional mean frequency (CMF) of the spectrogram of the sound, the change in the pitch of the bell has been discussed. With an accelerator, the vibration distributions on the different points of the bell have been measured. With short time spectrum analysis, the vibrational modes at different frequencies have been reconstructed.     

Simultaneous spectrum and coherent combining by active phasing dual two-tone all-fiber MOPA chains

We present a new approach for simultaneous spectral and coherent combining in a master oscillator power amplifier (MOPA) configuration with active phasing. Spectrally combined single-frequency seed lasers are employed as a master oscillator for the all-fiber power amplifier chain, which provides robust performance suppressing of the stimulated Brillouin scattering effect, while coherent combining of spectrally combined amplifiers with active phase control provides stable in-phase combining, despite the strong phase fluctuation. In experiments, two spectrally combined seed MOPA chains are coherently combined with a total output power of 390 W. The power of the main lobe in the closed loop is two times of that value in the open loop, and visibility of more than 75% of the long-exposure interference pattern at the receiving plane is obtained.     

Tunable diode lasers and two-tone frequency modulation spectroscopy applied to atmospheric gas analysis

In this paper, we discuss the main features of a class of gas analyzers based on spectroscopic techniques with the aim of realizing fully automated systems which can be used for practical purposes. The technique we deal with is based on semiconductor diode laser as sources, emitting in the near infrared region of the electromagnetic spectrum, and the two-tone frequency modulation spectroscopy as the detection technique. We will describe the main features of a typical device and two particular apparata for industrial and biological applications.     

Auditory temporal processing: two-tone flutter fusion and a model of temporal integration

Auditory temporal processing was examined using a flutter-fusion paradigm in which two tones were separated by a silent interval. The listener's task was to judge when the two tones, presented in a background noise, fused perceptually. The fusion point was studied in a series of six experiments. In the first five experiments, the duration of the first stimulus (T1) was the dependent variable. In the last experiment, the duration of the second stimulus (T2) was the dependent variable. An inverse relationship was found between T1 duration and the interstimulus interval (ISI) such that, when ISI was decreased, T1 duration had to be increased to maintain fusion. When ISI was plotted as a function of T1 duration, the data were represented by a negative exponential equation. Increasing the level of the tones, increasing the bandwidth of the background noise, or presenting the stimuli dichotically lowered the duration of T1 necessary for fusion. Changing the frequency of the tones had no effect on fusion. Decreasing the duration of T2 and holding T1 constant also resulted in fusion. A neurophysiological model implicating ON and OFF neural response interactions is postulated to account for the data.     

Harmonic and intermodulation distortions and noise associated with two-tone modulation of high-speed semiconductor lasers

We present results of modeling and simulation of the harmonic and intermodulation distortions as well as the intensity noise of high-speed semiconductor lasers under two-tone modulation. Multiple quantum-well lasers are considered, which are characterized by large differential gain and a modulation bandwidth of about 25GHz. The study is based on the rate equation model of semiconductor lasers excited by injection current with two sinusoidal tones separated by a radio frequency. The modulated laser signal is modeled in both the time and frequency domains. The time domain characteristics include the fluctuating waveform, while the frequency domain characteristics include the frequency spectrum of the relative intensity noise (RIN), carrier-to-noise ratio, modulation response, harmonic distortion, and the second- and third-order intermodulation distortions (IMD2 and IMD3). The analysis is performed for three frequencies of 5, 15, and 24 GHz, which are, respectively, lower, comparable, and higher than the laser relaxation frequency. The range of the modulation depth covers the regimes of small and large-signal modulation. We show that both RIN and IMD3 of two-modulated laser are minimum when the modulation frequency is 5GHz, and maximum when the modulation frequency is 24 GHz. The second-order harmonic distortion, IMD2, and IMD3 values are larger in the vicinity of relaxation oscillations and increase with the modulation index, especially under large-signal modulation.     

增益竞争双波长放大单频光纤放大器理论研究

引入增益竞争是抑制单频光纤放大器中受激布里渊散射(SBS)的有效方式. 在单频光纤放大器的基础上, 推导了描述增益竞争双波长放大单频掺镱双包层光纤放大器的稳态速率方程组, 建立了增益竞争双波长放大单频光纤放大器的理论模型; 利用建立的理论模型模拟分析了信号光波长间隔、 信号光种子功率比、 抽运方式和增益光纤长度等因素对放大器的单频激光输出 效率以及SBS抑制效果的影响.