Digitally Filtered Research Articles

A Novel Dentary Bone Conduction Device Equipped with Laser Communication in DSP.

In this study, we designed a dentary bone conduction system that transmits and receives audio by laser. The main objective of this research was to propose a complete hardware design method, including a laser audio transmitter and receiver and digital signal processor (DSP) based digital signal processing system. We also present a digital filter algorithm that can run on a DSP in real time. This experiment used the CMU ARCTIC databases’ human-voice reading audio as the standard audio. We used a piezoelectric sensor to measure the vibration signal of the bone conduction transducer (BCT) and separately calculated the signal-to-noise ratio (SNR) of the digitally filtered audio output and the unfiltered audio output using DSP. The SNR of the former was twice that of the latter, and the BCT output quality significantly improved. From the results, we can conclude that the dentary bone conduction system integrated with a DSP digital filter enhances sound quality.

Nonlinear inverse heat conduction: Digitally filtered space marching with phase-plane and cross-correlation analyses

ABSTRACTThis paper utilizes concepts extracted from phase-plane and cross-correlation analyses for estimating the optimal regularization parameter required by a nonlinear space marching inverse heat conduction method. The regularization parameter for this approach is based on the cut-off frequency used in a low-pass Gauss digital filter for preprocessing the in-depth temperature data. The simulation uses two in-depth thermocouples which are representative of a physical experiment. Numerical results indicate a high level of robustness as the best prediction is extracted from the prediction space over the spectrum of cut-off frequencies. The feasibility and effectiveness of phase-plane and cross-correlation analyses are discussed.

A time-domain noise-coupling technique for continuous-time sigma-delta modulators

In this paper, a time-domain noise-coupling technique based on the pulse width modulation is proposed. The time-domain quantization error is digitally extracted and shaped by an asynchronous digital filter. This digitally filtered quantization error is applied to the quantizer input to increase the modulator's noise-shaping order. By using this technique in continuous-time sigma-delta modulators, the modulator's shaping property is significantly enhanced. Comparative analytical calculations and simulation results are presented to estimate the performance of modulators employing the proposed quantizer. System-level simulation results reveal a (L + 2)th order noise-shaping capability of the proposed modulator while it employs only L analog integrators. The effects of main circuit non-idealities in the modulator's performance are analytically investigated and confirmed by the simulation results.

Classification of polymers insulators hydrophobicity basead on digital image processing

Although the hydrophobicity is usually an arduous parameter to be determined in the field, it has been pointed out as a good option to monitor aging of polymeric outdoor insulators. Concerning this purpose, digital image processing of photos taken from wet insulators has been the main technique nowadays. However, important challenges on this technique still remain to be overcome, such as; images from non-controlled illumination conditions can interfere on analyses and no existence of standard surfaces with different levels of hydrophobicity. In this paper, the photo image samples were digitally filtered to reduce the illumination influence, and hydrophobic surface samples were prepared from wetting silicon surfaces with solution of water-alcohol. Furthermore norevious studies triying to quantify and relate these properties in a mathematical function were found, that could be used in the field by the electrical companies. Based on such considerations, high quality images of countless hydrophobic surfaces were obtained and three different image processing methodologies, the fractal dimension and two Haralick textures descriptors, entropy and homogeneity, associated with several digital filters, were compared. The entropy parameter Haralick’s descriptors filtered with the White Top-Hat filter presented the best result to classify the hydrophobicity.

Indian summer monsoon simulation studies with different orographic representations in a spectral GCM

AbstractThe current study focuses on two aspects of the representation of orography in a spectral general circulation model (GCM). The most important issue is the reduction of the ripple effect, especially the oceanic surface deformations, which can create tendency for unrealistic oceanic rainfall patches in the model climate. In this study, seven types of digital filters were tried at horizontal resolution equivalent to spectral truncation at T80 to identify the most effective filter. Digital filtering results in much greater reduction in orographic barrier, and hence, the blocking effect compared to mean orography. The second point is retention of the barrier effect. In the past, several attempts have been made to address this. Techniques have been developed in the past to construct an optimal orography, to enable more region‐specific enhancement of mountains with less impact over oceans and plains. These techniques include site‐specific kernels and the cost‐function‐minimization. An attempt has been made in the current study to develop a digitally filtered, locally enhanced, optimal orography called the Filtered‐Modified Orography (FMO), for its application to Indian summer monsoon simulation. A number of sensitivity experiments have been conducted to determine the possible impacts of FMO on the seasonal simulation and the medium‐range prediction of Indian summer monsoon. Results of this study show that two‐dimensional (2‐D) Lanczos filter is the most effective in reducing the ripples and the associated errors in the orographic representation. FMO is able to enhance the peaks of the Himalayan range and Western Ghats, and in consequence, it produces a better simulation of Indian summer monsoon circulation features and the associated rainfall in the seasonal and medium time scale. This procedure for local enhancement is found to be more beneficial than global enhancement of orography in a spectral GCM so far as the regional weather prediction is concerned. Copyright © 2008 Royal Meteorological Society

Airborne passive Fourier transform infrared remote sensing of methanol vapor from industrial emissions

Passive Fourier transform infrared (FT-IR) remote sensing measurements are applied to the detection of methanol vapor plumes released from a chemical manufacturing facility. With the spectrometer mounted in a downward-looking mode on a fixed-wing aircraft, overflights of the facility are made during the methanol release. Signal processing and pattern recognition methods are applied to the acquired data for the purpose of constructing an automated classification algorithm for the methanol detection. The analysis is based on the use of short, digitally filtered segments of the raw interferogram data collected by the spectrometer. The classifiers are trained with data collected on the ground by use of an experimental protocol designed to simulate background conditions observed from the air. Optimization of the digital filtering and interferogram segment parameters leads to successful classifiers based on 100 or 120 interferogram points. The optimal interferogram segment location is found to be 95-points displaced from the centerburst, and the best performing digital filters are centered on the methanol C-O stretching band at 1036 cm(-1) and have a passband full-width at half-maximum of 100 to 160 cm(-1). The best classifiers achieve classification errors of less than 1% and are observed to be resistant to possible interference effects from species such as ethanol and ozone. This work demonstrates the utility of airborne passive FT-IR remote sensing measurements of volatile organic compounds under complex background conditions such as those encountered while monitoring an operating industrial facility.

Subjective image quality of digitally filtered radiographs acquired by the Dürr Vistascan system compared with conventional radiographs

To compare the different digital filters implemented in the Dürr Vistascan system with conventional film and to analyze the filter specificity to anatomic structures. Ten panoramic image pairs and 10 periapical image pairs (1 digital and 1 conventional) were obtained from 20 patients conventionally and digitally. The display quality of different anatomic image structures was rated subjectively on a 5-point scale. The responses were evaluated using ANOVA and Tukey-Kramer post hoc tests. The intraobserver reliability was evaluated by Cohen's kappa statistics. The display quality of anatomic structures was rated higher by using Caries 1 or 2 filters for periapical and Periodontal 1 or 2 filters for panoramic images, whereas nonfiltered and Noise Reduction-filtered images received the lowest scorings compared to all other digital image modalities (P < or = .0097). The superiority of conventional radiographs to the digital ones was statistically significant (P < or = .0039 and P < or = .0152 respectively). Depending on the diagnostic task, digital images of the Vistascan system should be filtered before examination. Perfect conventional radiographs still remain the gold standard for image quality.

Parametrization of Reversible Digitally Filtered Molecular Dynamics Simulations.

Reversible Digitally Filtered Molecular Dynamics (RDFMD) is a method of amplifying or suppressing motions in a molecular dynamics simulation, through the application of a digital filter to the simulation velocities. RDFMD and its derivatives have been previously used to promote conformational motions in liquid-phase butane, the Syrian hamster prion protein, alanine dipeptide, and the pentapeptide, YPGDV. The RDFMD method has associated with it a number of parameters that require specification to optimize the desired response. In this paper methods for the systematic analysis of these parameters are presented and applied to YPGDV with the specific emphasis of ensuring a gentle and progressive method that produces maximum conformation change from the energy put into the system. The portability of the new parameter set is then shown with an application to the M20 loop of E-coli dihydrofolate reductase. A conformational change is induced from a closed to an open structure similar to that seen in the DHFR-NADP(+) complex.

Application of the Hilbert−Huang Transform to the Analysis of Molecular Dynamics Simulations

The Hilbert-Huang transform (HHT) is a new method for the analysis of nonstationary signals that allows a signal's frequency and amplitude to be evaluated with excellent time resolution. In this paper, the HHT method is described, and its performance is compared with the Fourier methods of spectral analysis. The HHT is then applied to the analysis of molecular dynamics simulation trajectories, including enhanced sampling trajectories produced by reversible digitally filtered molecular dynamics. Amplitude-time, amplitude-frequency, and amplitude-frequency-time spectra are all produced with the method and compared to equivalent results obtained using wavelet analysis. The wavelet and HHT analysis yield qualitatively similar results, but the HHT provides a better match to physical intuition than the wavelet transform. Moreover the HHT method is able to show the flow of energy into low-frequency vibrations during conformational change events and is able to identify frequencies appropriate for amplification by digital filters including the observation of a 10 cm(-1) shift in target frequency.

Reversible Digitally Filtered Molecular Dynamics

It has recently been shown that digital filtering methods may be used to selectively enhance or suppress the vibrational motion in a molecular dynamics computer simulation solely on the basis of frequency (J. Chem. Phys. 2000, 112, 2586-2597). The method of digitally filtered molecular dynamics (DFMD) does, however, suffer from a number of disadvantages, the most important of which is the rapid redistribution of energy from the selected frequency range in condensed phase simulations. Here, an extension of the DFMD method that solves this problem, reversible digitally filtered molecular dynamics (RDFMD), is presented. In RDFMD, the digital filter is applied successively to velocities that have been generated from previous applications of the filter, by the simple expedient of running simulations both forward and backward in time to fill the filter buffer after each filter application. In this way, kinetic energy is added slowly to the system, with the result that the conformational transitions observed are more controlled and realistic. The method is applied to a number of systems of increasing complexity including alanine dipeptide in gas and condensed phases. These studies demonstrate the advantage of adding energy gradually and also reveal a change in the characteristic frequency of critical vibrations as the transition state is approached. A protocol for applying RDFMD to protein systems has also been devised and tested on the YPGDV pentapeptide in water.

Prototype neural semicircular canal prosthesis using patterned electrical stimulation.

The design of a prototype semicircular canal prosthesis is presented along with preliminary results. This device measures angular velocity of the head (+/-500 degrees/s) using a piezoelectric vibrating gyroscope. With a digital filter this velocity is filtered to match the dynamic characteristics of the semicircular canals, which are the physiological rotation sensors of the vestibular system. This digitally filtered signal is used to modulate the pulse rate of electrical stimulation. The pulse rate is varied between 50 and 250 Hz via a sigmoidal lookup table relating pulse rate to angular velocity; the steady-state rate is 150 Hz. A current source utilizes these timing pulses to deliver charge balanced, cathodic-first, biphasic, current pulses to the nerves innervating the semicircular canal via platinum electrodes. Power is supplied via lithium batteries. dc/dc converters are used to generate regulated +/-5 V supplies from the batteries. All of the components are contained in a small, lightweight, Nylon box measuring roughly 43 mm x 31 mm x 25 mm, which can be mounted on the top of an animal's head. This device has been tested in guinea pigs having surgically implanted platinum electrodes, and the results show that the prosthesis can provide a rotational cue to the nervous system.

Digitally filtered molecular dynamics: The frequency specific control of molecular dynamics simulations

A new method for modifying the course of a molecular dynamics computer simulation is presented. Digitally filtered molecular dynamics (DFMD) applies the well-established theory of digital filters to molecular dynamics simulations, enabling atomic motion to be enhanced or suppressed in a selective manner solely on the basis of frequency. The basic theory of digital filters and its application to molecular dynamics simulations is presented, together with the application of DFMD to the simple systems of single molecules of water and butane. The extension of the basic theory to the condensed phase is then described followed by its application to liquid phase butane and the Syrian hamster prion protein. The high degree of selectivity and control offered by DFMD, and its ability to enhance the rate of conformational change in butane and in the prion protein, is demonstrated.

Digital hearing impairment simulation method and hearing aid evaluation method using the same

A digital hearing impairment simulation method and a hearing aid evaluation method using the same are disclosed. According to the digital hearing impairment simulation method, a hearing characteristic table of a hearing impaired person is input and the input table is stored in a memory, in order to sample the hearing characteristics of the hearing impaired person (S1). A hearing loss table is calculated and stored in the memory (S2). An audio signal input via an audio input portion is converted to a digital signal and the converted digital signal is stored in the memory (S3). The converted digital signal is converted to the frequency domain signal using a fast Fourier transform algorithm (S4). The average power by critical band is calculated (S5). A hearing loss gain for each critical band is calculated using the hearing loss table and the average powers of the critical bands (S6). Coefficients for a digital filter corresponding to the hearing loss gains of the critical bands is calculated (S7). The input signal converted to a digital signal and stored in the memory in the step (S3) is digitally filtered using the digital filter coefficients (S8). The digitally filtered signal is converted to an analog signal and the converted analog signal is output to an audio output portion (S9). Thus, the performance of a hearing aid can be easily evaluated and hearing characteristics of a hearing impaired person can be easily sampled.

Measurement of glucose and other analytes in undiluted human serum with near-infrared transmission spectroscopy

Near-infrared calibration models are described for the measurement of total protein, albumin protein, globulin protein, triglycerides, cholesterol, urea, glucose, and lactate. Spectra are collected in triplicate over the 5000–4000 cm −1 spectral range with a 2.5 mm optical path length for 242 undiluted human serum samples. Calibration models are generated for each analyte by performing partial least-squares (PLS) regression on raw and digitally filtered spectra. Models are optimized individually for each analyte by considering spectral range, number of model factors and width/position of a Gaussian shaped filter response function for a digital Fourier filter. Accurate measurements are demonstrated for each analyte except lactate which is below the detection limit under our experimental conditions. Standard error of prediction (SEP) for glucose is 23.3 mg/dl (1.29 mM). Relevance and stability of the glucose calibration model are examined by evaluating the accuracy of glucose predictions from 50 human serum samples collected on a modified spectrometer nineteen months after the calibration data were collected. In addition, these 50 subsequent samples were treated in a blind manner by withholding their glucose values until all predictions were complete. Results indicate a slight positive bias in the predictions corresponding to a minor instability in the model. This instability is likely due to changes in the spectrometer hardware. Nevertheless, the strong correlation between predicted and actual glucose levels in these blind samples strongly suggests that this calibration model is based on information particular to glucose.

Fault scarp identification in side-scan sonar and bathymetry images from the Mid-Atlantic Ridge using wavelet-based digital filters

Digital filters designed using wavelet theory are applied to high resolution deep-towed side-scan sonar data from the median valley walls, crestal mountains, and flanks of the Mid-Atlantic Ridge at 29°10′ N. With proper tuning, the digital filters are able to identify the location, orientation, length, and width of highly reflective linear features in sonar images. These features are presumed to represent the acoustic backscatter from axis-facing normal faults. The fault locations obtained from the digital filters are well correlated with visual geologic interpretation of the images. The side-scan sonar images are also compared with swath bathymetry from the same area. The digitally filtered bathymetry images contain nine of the eleven faults identified by eye in the detailed geologic interpretation of the side-scan data. Faults with widths (measured perpendicular to their strike) of less than about 150 m are missed in the bathymetry analysis due to the coarser resolution of these data. This digital image processing technique demonstrates the potential of wavelet-based analysis to reduce subjectivity and labor involved in mapping and analyzing topographic features in side-scan sonar and bathymetric image data.

The effects of digital filtering on feline auditory brain-stem evoked potentials

The power spectrum of the feline auditory brain-stem evoked potentials (ABEPs) consists of 3 frequency bands, similar to the human wave form, but differing in range. The frequency bands in the feline spectra were separated by notches at 326 Hz and 732 Hz. Click-evoked ABEP from 15 cats were digitally filtered in 3 passbands: (1) below 326 Hz (‘slow filter’), (2) between 326 and 732 Hz (‘medium filter’); and (3) between 732 and 1790 Hz (‘fast filter’). Filtering in each of these bands differentially affected the ABEP components. The vertex positive components are labeled by their order of appearance, i.e., 1, 2,...5. Peak 1 is subdivided into 2 subcomponents labeled 1a and 1b. The slow filter was associated with the loss of all components leaving a slow potential shift, i.e., the ‘pedestal’ peaking at the latency of peak 4. The medium filter was associated with the loss of components 1a, 1b and 2, sparing 3 and 4. The fast filter was associated with the loss of 1b and a diminution of 2. Comparing cat and human ABEP, feline components 2, 3 and 4 behaved precisely the same as the human II, III and V. In contrast to the human I, the feline first component (1a) was not detected with the medium filter. No feline component, following peak 1 in the unfiltered wave form, disappeared with the slow and medium filters, and reemerged with the fast filter (as human IV does). Thus, based on the effects of digital filters on ABEP wave form, the human peak IV did not have a feline counterpart, and the feline bifid peak 1 differed compared to its human I counterpart. Some of these conclusions run counter to homologues suggested from lesion and depth recording experiments. Factors related to differences in the dimensions, composition, and orientation (relative to the recording electrodes) of the auditory pathway of humans and cats could affect the definition of homologues between the two species using filters as well as lesion and depth recordings.

Determination of physiological levels of glucose in an aqueous matrix with digitally filtered Fourier transform near-infrared spectra

A procedure is described for the measurement of clinically relevant concentrations of glucose in aqueous solutions with near-infrared (NIR) absorbance spectroscopy. A glucose band centered at 4400 cm-1 is used for this analysis. NIR spectra are collected over the frequency range 5000-4000 cm-1 with a Fourier transform spectrometer. A narrow-band-pass optical interference filter is placed in the optical path of the spectrometer to eliminate light outside this restricted range. This configuration provides a 2.9-fold reduction in spectral noise by utilizing the dynamic range of the detector solely for light transmitted through the filter. In addition, a novel spectral processing scheme is described for extracting glucose concentration information from the resulting absorbance spectra. The key component of this scheme is a digital Fourier filter that removes both high-frequency noise and low-frequency base-line variations from the spectra. Numerical optimization procedures are used to identify the best location and width of a Gaussian-shaped frequency response function for this Fourier filter. A dynamic area calculation, coupled with a simple linear base-line correction, provides an integrated area from the processed spectra that is linearly related to glucose concentrations over the range 1-20 mM. The linear calibration model accurately predicted glucose levels in a series of test solutions with an overall mean percent error of 2.5%. Based on the uncertainty in the parameters defining the calibration model and the variability of the magnitudes of the integrated areas, an overall uncertainty of 7.8% was estimated for predicted glucose concentrations.

Short latency somatosensory and spinal evoked potentials: Power spectra and comparison between high pass analog and digital filter

Medium nerve somatosensory evoked potentials (SSEPs) and intraoperative spinal evoked potentials were analyzed using different analog and zero phase shift digital high pass filter and by power spectrum. Additionally, high pass analog and digital filtering was performed on various sine, triangular and rectangular waves manufactured by a wave form generator. Recordings were also transformed to the 1st and 2nd time derivatives. The great abundance of spectral energy for scalp recorded median nerve SSEPs was below 125 c/sec but lower energy fast frequency components consistently extended to 500 c/sec. Power spectrum of the Erb's point compound nerve action potential revealed a wide band of spectral energy commencing at about 50–100 c/sec, peaking at about 250–270 c/sec and extending to nearly 1000 c/sec. This suggests that synchronous axonal activity generates predominantly faster frequencies above 100 c/sec. High pass analog filter confers phase non-linearity which results in various distortions including latency shift and a morphological change which may be visually similar to the 1st or 2nd time derivatives. High pass zero phase shift digital filter removes selected low frequencies without accompanying phase distortion. This accentuates fast peaks seen at open bandpass as well as transition points between baseline and component ascent or descent. Zero phase shift digital filter may also generate peaks that are not visualized at open pass but which reflect the sum of frequencies which were not removed by filtering. These peaks do not necessarily correspond to discrete singular neuroanatomical structures. Although peaks observed in high pass analog and digital filter appear similar and comparable, their underlying activity may be of different origin. This is because high pass analog filter projects a considerable amount of overlap from earlier onto later waves. For clinical correlation it is important that restricted bandpass analog or digitally filtered recordings be compared with open pass data. Only those peaks visualized in both open and restricted bandpass can be considered authentic. Examples of spinal and scalp SSEPs indicate that selective filtering may, under certain circumstances, distinguish axonal or lemniscal from synaptic generators.

Computer implemented digital filtering, scaling and addition for analysing the structure of early somatosensory evoked responses

Computer-implemented digital filters are used to separate the fast wave complexes which are superimposed on slower background waves in human short latency somatosensory evoked responses (SSERs). The choice of filter for picking out the fine structure of the fast wave is shown to be not critical. After scaling and adding digitally filtered SSERs from two electrode montages, the peaks believed to be of cortical origin are cancelled, leaving visible a repetitive wave which must be presumed to be generated subcortically. From this, a new interpretation of the origins of peaks in short latency SSERs is made.

Measurement of ventilation using digitally filtered transthoracic impedance.

A seven-stage low-pass digital filter was used to remove the cardiac artifact and motion interference from a respiratory transthoracic impedance signal in human subjects. After removal of these artifacts, the mean difference from a conventional gasometer technique fell from 5% to 1.6%. When the impedance technique was used to measure ventilation during air breathing, the addition of a breathing valve with a mouthpiece and noseclip induced the following changes in ventilatory parameters: 7% drop in frequency, 24% increase in tidal volume, 49% increase in inspiratory time, 56% increase in expiratory time, 10% decrease in inspiratory flow rate, and 4% decrease in ratio of respiratory time to total breath duration. These alterations were not significant at elevated inspired CO2 levels. The digitally filtered transthoracic impedance technique provides an accurate technique for measuring ventilatory parameters without the perturbations induced by using a conventional breathing valve technique even when cardiac and motion artifacts were prominent.