Average Group Delay Research Articles

Wideband coplanar waveguide to edges-even broadside-coupled stripline transition

A wideband transition between a coplanar waveguide (CPW) and an edges-even broadside-coupled stripline (EEBCS) is proposed. The simple transition is composed of a linear tapered line on the top layer and an electromagnetically-coupled Y-shaped stub on the bottom layer. A back-to-back, 50 Ω CPW to 100 Ω EEBCS transition is simulated, fabricated and measured. It is reported that a maximum insertion loss of 2.4 dB, a return loss better than −10 dB and average group delay of about 0.5 ns are obtained from 1.1 to 11.2 GHz for the transition.

All-Order Polarization-Mode-Dispersion (PMD) Compensation at 40 Gb/s via Hyperfine Resolution Optical Pulse Shaping

For the first time, we report lightwave system experiments testing a concept for all-order polarization-mode-dispersion (PMD) compensation based on optical pulse shaping. Our results demonstrate compensation of PMD with > 50-ps average differential group delay, well into the all-order regime, in a 40-Gb/s return-to-zero on-off keying experiment.

Middle ear function and cochlear input impedance in chinchilla

Simultaneous measurements of middle ear-conducted sound pressure in the cochlear vestibule P(V) and stapes velocity V(S) have been performed in only a few individuals from a few mammalian species. In this paper, simultaneous measurements of P(V) and V(S) in six chinchillas are reported, enabling computation of the middle ear pressure gain G(ME) (ratio of P(V) to the sound pressure in the ear canal P(TM)), the stapes velocity transfer function SVTF (ratio of the product of V(S) and area of the stapes footplate A(FP) to P(TM)), and, for the first time, the cochlear input impedance Z(C) (ratio of P(V) to the product of V(S) and A(FP)) in individuals. mid R:G(ME)mid R: ranged from 25 to 35 dB over 125 Hz-8 kHz; the average group delay between 200 Hz and 10 kHz was about 52 mus. SVTF was comparable to that of previous studies. Z(C) was resistive from the lowest frequencies up to at least 10 kHz, with a magnitude on the order of 10(11) acoustic ohms. P(V), V(S), and the acoustic power entering the cochlea were good predictors of the shape of the audiogram at frequencies between 125 Hz and 2 kHz.

Voice conversion by mapping the speaker-specific features using pitch synchronous approach

The basic goal of the voice conversion system is to modify the speaker-specific characteristics, keeping the message and the environmental information contained in the speech signal intact. Speaker characteristics reflect in speech at different levels, such as, the shape of the glottal pulse (excitation source characteristics), the shape of the vocal tract (vocal tract system characteristics) and the long-term features (suprasegmental or prosodic characteristics). In this paper, we are proposing neural network models for developing mapping functions at each level. The features used for developing the mapping functions are extracted using pitch synchronous analysis. Pitch synchronous analysis provides the estimation of accurate vocal tract parameters, by analyzing the speech signal independently in each pitch period without influenced by the adjacent pitch cycles. In this work, the instants of significant excitation are used as pitch markers to perform the pitch synchronous analysis. The instants of significant excitation correspond to the instants of glottal closure (epochs) in the case of voiced speech, and to some random excitations like onset of burst in the case of nonvoiced speech. Instants of significant excitation are computed from the linear prediction (LP) residual of speech signals by using the property of average group-delay of minimum phase signals. In this paper, line spectral frequencies (LSFs) are used for representing the vocal tract characteristics, and for developing its associated mapping function. LP residual of the speech signal is viewed as excitation source, and the residual samples around the instant of glottal closure are used for mapping. Prosodic parameters at syllable and phrase levels are used for deriving the mapping function. Source and system level mapping functions are derived pitch synchronously, and the incorporation of target prosodic parameters is performed pitch synchronously using instants of significant excitation. The performance of the voice conversion system is evaluated using listening tests. The prediction accuracy of the mapping functions (neural network models) used at different levels in the proposed voice conversion system is further evaluated using objective measures such as deviation ( D i ) , root mean square error ( μ RMSE ) and correlation coefficient ( γ X , Y ). The proposed approach (i.e., mapping and modification of parameters using pitch synchronous approach) used for voice conversion is shown to be performed better compared to the earlier method (mapping the vocal tract parameters using block processing) proposed by the author.

Integrated Bluetooth and UWB Antenna

A small-sized, low-profile, and planar integrated Bluetooth and ultrawideband (UWB) antenna is presented. The antenna exhibits a dual-band operation covering 2400-2484 MHz (Bluetooth) and 3100-10600 MHz (UWB) frequency bands. It is fed by a microstrip line and built on a FR-4 substrate with 42times46 mm2 surface area. The impedance, radiation, phase linearity, and impulse response properties of the antenna are studied both theoretically and experimentally. The calculated and measured results agree well. The antenna shows acceptable gain flatness with stable omnidirectional radiation patterns across the integrated Bluetooth and UWB bands. The average group delay is approximately 0.2 ns across UWB frequencies. The impulse response is very good, with some level of ringing observed.

Distributed PMD Compensation Experiment Using Polarizers

We experimentally demonstrated polarization-mode dispersion (PMD) compensation by distributing polarizers with only 1 degree of freedom (DOF) along the transmission line. The average power penalty was measured to be 0.4 dB by inserting four compensators, where average differential group delay was 47% of bit period.

Prosody modification using instants of significant excitation

Prosody modification involves changing the pitch and duration of speech without affecting the message and naturalness. This paper proposes a method for prosody (pitch and duration) modification using the instants of significant excitation of the vocal tract system during the production of speech. The instants of significant excitation correspond to the instants of glottal closure (epochs) in the case of voiced speech, and to some random excitations like onset of burst in the case of nonvoiced speech. Instants of significant excitation are computed from the linear prediction (LP) residual of speech signals by using the property of average group-delay of minimum phase signals. The modification of pitch and duration is achieved by manipulating the LP residual with the help of the knowledge of the instants of significant excitation. The modified residual is used to excite the time-varying filter, whose parameters are derived from the original speech signal. Perceptual quality of the synthesized speech is good and is without any significant distortion. The proposed method is evaluated using waveforms, spectrograms, and listening tests. The performance of the method is compared with linear prediction pitch synchronous overlap and add (LP-PSOLA) method, which is another method for prosody manipulation based on the modification of the LP residual. The original and the synthesized speech signals obtained by the proposed method and by the LP-PSOLA method are available for listening at http://speech.cs.iitm.ernet.in/Main/result/prosody.html.

Enhanced polarization mode dispersion tolerance by optimizing receiver bandwidth

We report our theoretical analysis on polarization mode dispersion (PMD) tolerance of the return-to-zero transmission system under error-free [bit error rate (BER) 10–12] conditions. The results show that the tolerable PMD cannot be further enhanced by increasing the receiver power margin when forward error correction is used. The investigation also reveals that optimal receiver bandwidth for minimum BER should be increased accordingly when the accumulated PMD is increased. By designing the receiving filter with adaptive bandwidth, the acceptable average differential group delay can be improved by up to 2% of the bit interval.

Polarization-mode dispersion compensation in WDM systems

We demonstrate, both experimentally and numerically, polarization-mode dispersion (PMD) compensation in wavelength-division-multiplexing (WDM) systems without wavelength demultiplexing. Our technique improves the overall system performance by reducing the fading probability for the worst-performing channel at any given time. The effectiveness of our approach is based on the fact that, for moderate PMD, the probability that all channels are severely degraded at the same time is extremely small. A single-section PMD compensator reduces the 2% worst-case power penalty for a four-channel 10-Gb/s WDM system with /spl sim/42 ps average differential group delay from 9.6 to 5.3 dB.

Delay analysis in the auditory brainstem of the rat: comparison with click latency

Many cells in the auditory brainstem ‘phase lock’ to tone stimuli. From the changing phase relationship between the stimulus and the neural response in phase-locking cells, the delay between them can be estimated. This delay, however, is consistently greater than the latency measured in response to click stimuli, an important discrepancy. In this paper the different measures of delay, namely phase delay, group delay and signal-front delay are re-examined. An improved method for computing the average group delay is presented, which accounts for the cyclical nature of the phase data. Data were collected from units in successive processing sites of auditory pathway: the auditory nerve, the cochlear nucleus, the trapezoid body and the medial nucleus of the trapezoid body. Low-characteristic frequency (CF) units gave multimodal post-stimulus-time histograms in response to clicks, and showed stepwise decreases in latency with increasing intensity, with the appearance of earlier peaks in the response, rather than shifts in the timing of the peaks. The separation of peaks corresponded to the inverse of the unit’s CF. High-CF units also showed a decline in click latency with intensity, but to a lesser degree than low CF units. We present an analysis which explains the difference between click latency and delay, and which in contrast to previous accounts is experimentally testable. We demonstrate that this new framework accounts for the discrepancy between the two measures of delay, and in addition accounts for the observed stepwise shifts in click latency for low-CF units.

In-field comparison among polarization-mode-dispersion measurement techniques

We report polarization mode dispersion measurements on a 168 km long undersea optical cable, performed with two techniques. From experimental results, statistical behavior of polarization parameters and their time fluctuations have been extracted. An average differential group delay of about 13 ps shows that dispersion-shifted fibers can be affected by a polarization dispersion significantly larger than standard step-index fibers. The correlation length of the polarization-coupling perturbation in the tested fibers is not negligible with respect to the link length.

Systematic errors in indirect estimates of basilar membrane travel times.

There exist in the literature three attempts to derive basilar membrane travel times from the phase versus frequency characteristics of responses to tones in the auditory nerve [Anderson et al., J. Acoust. Soc. Am. 4., 1131-1139 (1971)], cochlear nucleus [Gibson et al., in Psychophysics and Physiology of Hearing, edited by Evans and Wilson (Academic, New York, 1977), pp. 57-68], and basilar membrane [Robles et al., J. Acoust. Soc. Am. 59, 926-939 (1976)]. It is argued in this paper that these derivations probably have overestimated the actual mechanical travel times. Travel time was originally defined by von Békésy as the latency between the onset of a click stimulus and the onset of basilar membrane vibration. For a linear bandpass system, the frequency-domain equivalent of this latency is the high-frequency asymptotoic slope of the phase lag versus frequency characteristic, which is not generally a linear function. In the neural studies (auditory nerve and cochlear nucleus) it was assumed that the phase versus frequency characteristic was a straight line. Slopes derived under a linear assumption are probably closer to the weighted average group delay (i.e., the center of gravity of the click response) than they are to travel time. In the Mössbauer study of basilar membrane mechanics the latency of the response to clicks was compared with the low-frequency slope of the phase characteristic. The comparison should have been made with the high-frequency slope.