Impulse Response Measurements Research Articles

Tera-sample-per-second single-shot device analyzer.

With the ever-increasing need for bandwidth in data centers and 5G mobile communications, technologies for rapid characterization of wide-band devices are in high demand. We report an instrument for extremely fast characterization of the electronic and optoelectronic devices with 27 ns frequency-response acquisition time at the effective sampling rate of 2.5 Tera-sample/s and an ultra-low effective timing jitter of 5.4 fs. This instrument features automated digital signal processing algorithms including time-series segmentation and frame alignment, impulse localization and Tikhonov regularized deconvolution for single-shot impulse and frequency response measurements. The system is based on the photonic time-stretch and features phase diversity to eliminate frequency fading and extend the bandwidth of the instrument.

Measurement and Adaptive Identification of Nonstationary Acoustic Impulse Responses

In this work, we present a method of measurement of nonstationary acoustic impulse responses identified by the fast version of the Recursive Least Squares algorithm (FRLS), using professional acoustic equipment. This measurement bench realized in a deaf room presents several tests of capability of adaptive algorithm to tracking the nonstationarities of true system to be identified. The tests of tracking capability obtained are stronger compared to what is encountered in real life and can be used in several applications.

Millimeter-Wave Base Station Diversity for 5G Coordinated Multipoint (CoMP) Applications

Millimeter-wave (mmWave) will be used for fifth-generation (5G) wireless systems. While many recent empirical studies have presented propagation characteristics at mmWave bands, macrodiversity and Coordinated Multipoint (CoMP) have not been carefully studied. This paper describes a large-scale mmWave base station diversity measurement campaign at 73 GHz in an urban microcell (UMi) in downtown, Brooklyn, NY, USA, and provides the first detailed analysis of CoMP and macrodiversity performance based on extensive measurements. The research employed nine different base station locations in a 200 m by 200 m area and considered 36 individual transmitter-receiver combinations for extensive co- and cross-polarized varying directional beam channel impulse response measurements. From the measured data, hypothesis testing with cross-validation shows that large-scale shadow fading of directional path loss at an RX from multiple base stations can be modeled as being independent. To consider life-like human blockage in CoMP and macrodiversity analysis, simulated human blockage traces are superimposed on the directional measurements to quantitatively show that a user that is served by multiple base stations undergoes dramatically less outage in the presence of rapid fading events, compared to a single serving base station. Moreover, the base station diversity measurements are used to determine the effectiveness of downlink precoding techniques for mmWave CoMP. While results show that the coordination can improve network performance by suppressing interference when it exists, nearly half of the 680 000 directional CoMP measurements (~43%) result in no interference for either user, meaning that macrodiversity alone may offer sufficient link and capacity improvement and that CoMP may not be necessary for interference coordination at mmWave when narrow directional beams are used.

Archaeoacoustic Examination of Lazarica Church

The acoustic analysis provides additional information on building tradition and related indoor practice that includes sound, thus deepening our understanding of architectural heritage. In this paper, the sound field of the Orthodox medieval church Lazarica (Kruševac city, Serbia) is examined. Lazarica is a representative of Morava architectural style, developed in the final period of the Serbian medieval state, when also the chanting art thrived, proving the importance of the aural environment in Serbian churches. The church plan is a combination of a traditional inscribed cross and a triconch. After the in situ measurement of acoustic impulse response using EASERA software, we built a computer model in the acoustic simulation software EASE and calibrated it accordingly. Following the parameters (reverberation time (T30), early decay time (EDT) and speech transmission index (STI)), we examined the acoustic effect of the space occupancy, central dome and the iconostasis. In all the cases, no significant deviation between T30 and EDT parameter was observed, which indicates uniform sound energy decay. Closing the dome with a flat ceiling did not show any significant impact on T30, but it lowered speech intelligibility. The height of iconostasis showed no significant influence on the acoustics of Lazarica church.

Integrity Testing of Cast In Situ Concrete Piles Based on an Impulse Response Function Method Using Sine-Sweep Excitation by a Shaker

In this study, an Impulse Response Function analysis of pile response to sine-sweep excitation by a low cost, portable shaker was used to identify defects in piles. In straightforward impact-echo methods, echoes from the pile toe and defects are visible in the time domain measurements. However, these echoes are not present in the time domain records of piles subjected to sine-sweep excitations, due to interactions between the input and output signals. For this reason, the impulse response function in the time domain has been calculated and is able to identify the echoes from pile impedance changes. The proposed methodology has been evaluated both numerically and experimentally. A one-dimensional pile-soil interaction system was developed, and a finite difference method used to calculate the pile response to sine-sweep excitation. The numerical simulations indicate that impulse response measurements with a synthesized logarithmic, sine-sweep excitation could be an effective tool for detecting defects in piles. The methodology was further tested with field trials on 6 cast in situ concrete test piles including 1 intact pile and 5 defective piles subjected to sine-sweep excitations by a shaker. In 5 of the 6 cases the echoes from the pile toe could be identified in the deconvoluted waveforms—the impulse response functions. Damage detection is more difficult and dependent on the selection of the optimal regularization parameter. Further research and optimization of the deconvolution process is needed to evaluate the effectiveness compared to standard pile integrity testing methods.

A Compact Model for Si-Ge Avalanche Photodiodes Over a Wide Range of Multiplication Gain

Silicon-germanium (Si-Ge) avalanche photodiodes (APDs) have superior gain bandwidth product due to the low impact ionization ratio of silicon. To enable efficient optical transceiver systems, cosimulation environments are essential for optimization of optical devices and transceiver circuitry. A compact Si-Ge APD circuit model, which captures both electrical and optical dynamics over a wide range of multiplication gain, is presented. This model includes effects of carrier transit time, avalanche buildup time and electrical parasitics. Model parameters are extracted by small-signal measurement and impulse response measurement where three gain regimes are discussed corresponding to the different mechanisms of carrier transit time and electrical parasitics. Simulated and measured bandwidth versus gain have a good agreement for APD multiplication gains from M = 1 to M = 17. Excellent matching between simulated and measured 25 Gb/s eye diagrams at M = 2 and M = 5.9 is achieved.

Simultaneous mode-by-mode impulse response measurement of multi-mode optical systems based on linear optical sampling.

Linear optical sampling is presented as a useful method to characterize mode-by-mode impulse responses or the spectral transfer matrix of multimode optical systems. In a two non-degenerate linear-polarization (LP) mode transmission line, which actually supported six independent spatial modes, 6 × 6 spectral transfer functions were simultaneously measured using multiplexed mode-by-mode impulse responses in series. According to the singular value analysis of the matrix, the mode-dependent loss spectrum was analyzed over a frequency bandwidth of several hundred GHz, which was determined by the spectra of the probe and reference pulses. The technique would be useful for characterizing various multi-spatial-mode fiber systems that are intensively being developed to overcome the limit in capacity of single-mode optical fibers.

Measurement Stand and Methodology for Research of the Off-Body and Body-to-Body Radio Channels in WBANs with Different Diversity Schemes

The concept of an experimental test bed for system loss and channel impulse response measurements for off-body and body-to-body radio channels in wireless body area networks (WBANs) is fully described. The possible measurement scenarios that may occur in investigation of off-body and body-to-body channels are classified and described in detail. Additionally, an evaluation is provided of the standard and expanded uncertainties of the presented measurement stand and methodology. Finally, the exemplary results are presented and discussed, in order to point out the need for further investigations of different diversity schemes and their applications in WBANs.

Impact of Structural Parameters on the Auditory Perception of Musical Sounds in Closed Spaces: An Experimental Study

This study attempts to investigate the impact of structural parameters (volume, shape, and the wall absorption coefficient) in closed space on the auditory perception of three different musical sound types. With binaural audibility technology and room impulse response measurement (RIR), this paper first verifies the reliability of using ODEON software in simulating simplified closed-space auditory scenes. Then, 96 music binaural signals produced in eight simulated closed spaces with different structural parameters are synthesized. Finally, auditory perception experiment is conducted on the synthesized binaural signals by using pair comparison method, and variance analysis is also made on the experimental results. It is concluded that (1) a hemispherical cabin with a small volume and large wall sound absorption coefficient is most suitable for playing a single instrument, such as the flute or violin, and (2) a cabin with large volume is suitable for playing multiple instruments music such as symphony, but the walls should not be totally reflective. The experimental scheme and results of current study provide guidance for designing the inner structure of the concert hall to achieve preferable auditory perception in practice.

Impulse response of weakly-coupled multicore fiber measured by using high-dynamic-range linear optical sampling

Abstract We report the impulse response measurement of weakly-coupled homogeneous multicore fiber accomplished by coherence-recovered linear optical sampling, which simultaneously realizes a picosecond-level time resolution and a dynamic range of over 70 dB. The observed core-by-core impulse responses include a directly transmitted pulse and plateaus that are yielded by inter-core couplings. A consideration of the observed results suggests that the group velocities are perturbed, and the core with the slowest group velocity alters along the fiber. We also found that the polarization states of the plateaus alter in the time axis of the impulse response chart, with a correlation width as short as the pulse width: we presume that this phenomenon is observed because the polarization change that occurs during propagation is transferred to the coupled signals with the shrinkage of the time axis. Next, we selected a 100 m-long piece of fiber, and measured the group delay of each core. We found that the variation of the core-by-core group delays was not similar to that of the long fiber, and it may change considerably with bending induced in the fiber. These results also suggest a variation in the local group delays over the length of the fiber.

Perceptual evaluation of headphone auralization of rooms captured with spherical microphone arrays with respect to spaciousness and timbre.

A listening experiment is presented in which subjects rated the perceived differences in terms of spaciousness and timbre between a headphone-based headtracked dummy head auralization of a sound source in different rooms and a headphone-based headtracked auralization of a spherical microphone array recording of the same scenario. The underlying auralizations were based on measured impulse responses to assure equal conditions. Rigid-sphere arrays with different amounts of microphones ranging from 50 to up to 1202 were emulated through sequential measurements, and spherical harmonics orders of up to 12 were tested. The results show that the array auralizations are partially indistinguishable from the direct dummy head auralization at a spherical harmonics order of 8 or higher if the virtual sound source is located at a lateral position. No significant reduction of the perceived differences with increasing order is observed for frontal virtual sound sources. In this case, small differences with respect to both spaciousness and timbre persist. The evaluation of lowpass-filtered stimuli shows that the perceived differences occur exclusively at higher frequencies and can therefore be attributed to spatial aliasing. The room had only a minor effect on the results.

A round robin on room acoustical simulation and auralization.

A round robin was conducted to evaluate the state of the art of room acoustic modeling software both in the physical and perceptual realms. The test was based on six acoustic scenes highlighting specific acoustic phenomena and for three complex, "real-world" spatial environments. The results demonstrate that most present simulation algorithms generate obvious model errors once the assumptions of geometrical acoustics are no longer met. As a consequence, they are neither able to provide a reliable pattern of early reflections nor do they provide a reliable prediction of room acoustic parameters outside a medium frequency range. In the perceptual domain, the algorithms under test could generate mostly plausible but not authentic auralizations, i.e., the difference between simulated and measured impulse responses of the same scene was always clearly audible. Most relevant for this perceptual difference are deviations in tone color and source position between measurement and simulation, which to a large extent can be traced back to the simplified use of random incidence absorption and scattering coefficients and shortcomings in the simulation of early reflections due to the missing or insufficient modeling of diffraction.

Evaluating patient and staff perceptions of soundscape conditions within three hospitals

Hospitals can present challenging soundscapes due to the continuous activity found within these environments. Routinely, this leads to poor perceptions of acoustical conditions from both patients and staff, such as in nationally reported HCAHPS patient surveys or hospital-administered staff surveys. In fact, it has been found that patient satisfaction of in-room soundscape conditions is highly related to the overall hospital rating and that staff job performance and satisfaction can be negatively affected by the acoustical environments in which they work. This research addressed these issues by collecting acoustical measurements within 38 patient rooms from 11 units of three individual hospitals, comparing results with patient and staff survey information. Data collected included 24-h occupied sound monitoring of patient rooms and nursing stations, unoccupied BNL sound levels from 20 patient rooms, and impulse response measurements of hospital unit hallways. Results from statistical analyses between measured acoustical data and patient/staff surveys will be reported, along with lessons learned applicable across all three hospitals. Taken as a whole, this study provided new insights into patient and staff perceptions of hospital noise, and could ultimately aid in the design process of new hospitals to improve patient and staff satisfaction.

Auralization of virtual concerts: A subjective evaluation comparing binaural and ambisonic rendering

Auralization renderings have reached a sufficient level of maturity that simulated auralizations can be comparable to measured ones. These auralizations can be rendered over a variety of sound systems, potentially combined with a visual model through VR interfaces. This study presents a perceptual evaluation of auralizations of a small ensemble virtual concert rendering, comparing a tracked binaural rendering to 2nd order Ambisonic rendering over a 32 loudspeaker array. The geometrical acoustic model of several actual performance spaces were created and then calibrated using in situ omni-directional room impulse response measurements. The performance stimuli consisted of 3 extracts of jazz anechoic recordings comprising trios and quartet ensembles, augmented by three-dimensional visual point-clouds of the musicians playing on stage. Participants of the listening test included a range of listening expertise level (acousticians, architects, students). Several room acoustical parameters were evaluated between rendering systems, seating positions, and rooms.

Adaptive reuse of unconventional spaces for performance: Music in a museum and opera in a warehouse

Taking a space designed for one purpose and creating an acoustically sound space for musical performance presents unique challenges. A local opera company has undertaken two projects that involve such modifications for this performance season and have sought guidance on the unique acoustic complications involved. The first project was a percussive musical playground in a large art museum, adjacent to sound-sensitive exhibits. The second involved the adaptation of an existing warehouse into a space suitable for the performance of a ballet-opera. Researchers worked with set designers early in the process and throughout set construction. In order to better understand the spaces, impulse responses were taken and analyzed. Impulse response measurement results, acoustic models with suggested modifications, and auralizations at key listening positions are presented to address unique challenges associated with these unconventional spaces. An emphasis has been placed on reaching target values for reverberation time within limited time and resource constraints. Additionally, sound isolation for the two spaces has been addressed with special regard to adjacencies and noises in industrial downtown locations.

A method for conversational signal-to-noise ratio estimation in real-world sound scenarios

The analysis of conversational signal-to-noise ratios (SNRs) measured in real-world scenarios can provide vital insight into people's communicative strategies and difficulties and guide development of hearing devices. However, measuring SNRs accurately and realistically is challenging in typical recording conditions, where only a mixture of sound sources is captured. This study introduces a novel method for realistic in situ SNR estimation, where the speech signal of a person in natural conversation is captured by a cheek-mounted microphone, adjusted for free-field conditions, and convolved with a measured impulse response to estimate the clean speech component at the receiver. A microphone near the receiver computes the noise-only component by applying a voice activity detector. Obtained SNR values are analyzed using in situ recordings of a real-world workspace meeting. It is shown that the temporal resolution is increased, and fluctuations in the speech level are more accurately tracked compared to a typical spectral-subtraction-derived method. The application of the proposed SNR estimation method may be valuable for compensation procedures in hearing instruments that take conversational dynamics into account.

EVALUATION OF RAILWAY BALLAST LAYER CONSOLIDATION AFTER MAINTENANCE WORKS

The results of the study of the ballast layer consolidation after the work of ballast-tamping machines of different types are given in the article. The existing methods of determining the degree of consolidation of the ballast layer are analysed. The seismic method was improved by means of a complex dynamic and kinematic interpretation of the impulse response. For the dynamic interpretation with the use of statistical analysis, the features are selected so that they correspond to the degree of consolidation of the ballast layer. On the basis of researches, a device and software were developed that allow an automated evaluation of the ballast layer consolidation based on the kinematic and dynamic analysis of the measured impulse response. The measurements of the degree of the ballast layer consolidation after an operation of ballast-consolidation machines in different sequences allowed establishing the efficiency of the consolidation and the feasibility of the machines’ application.

Real-Time Geometry-Based Wireless Channel Emulation

Connected autonomous vehicles and industry 4.0 production scenarios require ultrareliable low-latency communication links. The varying positions of transmitter, reflecting objects, and receiver cause a nonstationary time- and frequency-selective fading process. In this paper, we present the necessary hardware architecture and signal processing algorithms for a real-time geometry-based channel emulator, that is needed for testing of wireless control systems. We partition the nonstationary fading process into a sequence of local stationarity regions and model the channel impulse response as sum of propagation paths with time-varying attenuation, delay, and Doppler shift. We implement a subspace projection of the propagation path parameters, to compress the time-variant channel impulse response. This enables a low data-rate link from the host computer, which computes the geometry-based propagation paths, to the software defined radio unit, that implements the convolution on a field programmable gate array (FPGA). With our new architecture, the complexity of the FPGA implementation becomes independent of the number of propagation paths. Our channel emulator can be parametrized by all known channel models. Without loss of generality, we use a parameterization by a geometry-based stochastic channel model, due to its nonstationary nature. We provide channel impulse response measurements of the channel emulator, using the RUSK Lund channel sounder for a vehicular scenario with 617 propagation paths. A comparison of the time-variant power delay profile and Doppler spectral density of simulated and emulated channel impulse response showed a close match with an error smaller than -35 dB. The results demonstrate that our channel emulator is able to accurately emulate nonstationary fading channels with continuously changing path delays and Doppler shifts.

Modelovanje frekvencijski zavisnog modela stubnog uzemljivača na osnovu merenja impulsnog odziva

Modelovanje frekvencijski zavisnog modela stubnog uzemljivača na osnovu merenja impulsnog odziva

Recent Advances in the Hardware of Visible Light Communication

Visible light communication (VLC) is an emerging technology that can transform lighting facilities into access points for wireless communication. Its development is bottlenecked by the cut-off frequencies (e.g., -6-dB electrical cut-off frequency f c and -3-dB electrical cut-off frequency f -3 dB ) of hardware, such as light-emitting diodes (LEDs), color converters, and photodetectors (PDs). In the past decade, especially in 2018, many materials and devices have been tested for properties related to VLC, such as f c , response time, and transmission data rates, which are listed and analyzed here to get an updated overall picture. The f -3 dB for the latest blue LED and color converter can reach up to 1485 and 470 MHz, respectively, which are great improvements from <;5 MHz for conventional white LEDs. Among the new PDs, the largest characterized f c is 4.2 MHz. Moreover, the smallest response time of these PDs is 0.95 ns, which is promising to have f c of hundreds of megahertz. The limitation in the field of view when the active area is reduced to enlarge f c of the PD can be partially overcome with novel fluorescent antenna, whose f c is more than 40 MHz. These increments in the f c or f -3 dB of hardware not only enlarge the channel capacity of the VLC but also facilitate the channel impulse response measurement, and the system becomes more susceptible to changes in the environment. These advances will shed light on the future development of the VLC with faster speed, more portable devices, and more applications for the Internet of Things.