Cutoff Frequency Of High-pass Filter Research Articles

Vibration characteristics and cross-feedback control of magnetically suspended blower based on complex-factor model

The research of vibration characteristics and active control methods of the magnetically suspended blower (MSB) are conducted for mitigation of the vibration amplitudes and the dynamic displacements of rotor shaft of the MSB at high speed. Firstly, the dynamic models with four degrees of freedom (DOFs) of the rotor shaft in the MSB are established. Secondly, the vibration characteristics of rotor shaft considering the rotor unbalance and misalignment are analyzed using the complex-factor model. Furthermore, the complex-factor and complex-exponential function cross-feedback models are respectively used to suppress the vibration amplitudes and the dynamic displacements of rotor shaft. Both numerical simulation and experimental tests of the cross-feedback model are conducted to verify the models. It is shown that a wide cutoff frequency of low-pass filter (LPF) could mitigate the precession, and a wide cutoff frequency of high-pass filter (HPF) could suppress the nutation. The proposed complex-exponential function cross-feedback model could be used to reduce the precession amplitude of the rotor shaft by 38.88%, and mitigate its nutation by 60.42%.

Easy detection for the high-pass filter cut-off frequency of digital ground motion record based on STA/LTA method: a case study in the 2008 Wenchuan mainshock

Easy detection for the high-pass filter cut-off frequency of digital ground motion record based on STA/LTA method: a case study in the 2008 Wenchuan mainshock

Energy management strategy with two degrees of freedom for hybrid energy storage systems in islanded DC microgrids

In this study, a novel energy management strategy (EMS) with two degrees of freedom is proposed for hybrid energy storage systems consisting of supercapacitor (SC) and battery in islanded microgrids. The proposal introduces two degrees of freedom including an adaptive high-pass filter cut-off frequency f c and a charge/discharge coefficient kb, according to the SC and battery state of charge (SOC), respectively. The f c regulates SC current in the transient process and the kb controls battery current in the steady-state. Therefore, appropriate power distribution that the SC suppresses the transient power fluctuations while the battery supports average power demand is realised, over-charging, and over-discharging are avoided and the current stress of the battery during the shut-down process is reduced. Moreover, three operation modes for isolated DC microgrids, comprising power-sharing mode, battery-only mode, and extreme mode are demonstrated. Hence, the DC microgrid can remain stable for the whole time, achieve seamless transitions from the power-sharing mode to the two others, and provide faster SOC recovery of the SC. The effectiveness of the proposed EMS is validated by experimental studies with a prototype of the simplified DC microgrid.

Human Frequency Following Responses to Filtered Speech.

There is increasing interest in using the frequency following response (FFR) to describe the effects of varying different aspects of hearing aid signal processing on brainstem neural representation of speech. To this end, recent studies have examined the effects of filtering on brainstem neural representation of the speech fundamental frequency (f0) in listeners with normal hearing sensitivity by measuring FFRs to low- and high-pass filtered signals. However, the stimuli used in these studies do not reflect the entire range of typical cutoff frequencies used in frequency-specific gain adjustments during hearing aid fitting. Further, there has been limited discussion on the effect of filtering on brainstem neural representation of formant-related harmonics. Here, the effects of filtering on brainstem neural representation of speech fundamental frequency (f0) and harmonics related to first formant frequency (F1) were assessed by recording envelope and spectral FFRs to a vowel low-, high-, and band-pass filtered at cutoff frequencies ranging from 0.125 to 8 kHz. FFRs were measured to a synthetically generated vowel stimulus /u/ presented in a full bandwidth and low-pass (experiment 1), high-pass (experiment 2), and band-pass (experiment 3) filtered conditions. In experiment 1, FFRs were measured to a synthetically generated vowel stimulus /u/ presented in a full bandwidth condition as well as 11 low-pass filtered conditions (low-pass cutoff frequencies: 0.125, 0.25, 0.5, 0.75, 1, 1.5, 2, 3, 4, 6, and 8 kHz) in 19 adult listeners with normal hearing sensitivity. In experiment 2, FFRs were measured to the same synthetically generated vowel stimulus /u/ presented in a full bandwidth condition as well as 10 high-pass filtered conditions (high-pass cutoff frequencies: 0.125, 0.25, 0.5, 0.75, 1, 1.5, 2, 3, 4, and 6 kHz) in 7 adult listeners with normal hearing sensitivity. In experiment 3, in addition to the full bandwidth condition, FFRs were measured to vowel /u/ low-pass filtered at 2 kHz, band-pass filtered between 2-4 kHz and 4-6 kHz in 10 adult listeners with normal hearing sensitivity. A Fast Fourier Transform analysis was conducted to measure the strength of f0 and the F1-related harmonic relative to the noise floor in the brainstem neural responses obtained to the full bandwidth and filtered stimulus conditions. Brainstem neural representation of f0 was reduced when the low-pass filter cutoff frequency was between 0.25 and 0.5 kHz; no differences in f0 strength were noted between conditions when the low-pass filter cutoff condition was at or greater than 0.75 kHz. While envelope FFR f0 strength was reduced when the stimulus was high-pass filtered at 6 kHz, there was no effect of high-pass filtering on brainstem neural representation of f0 when the high-pass filter cutoff frequency ranged from 0.125 to 4 kHz. There was a weakly significant global effect of band-pass filtering on brainstem neural phase-locking to f0. A trends analysis indicated that mean f0 magnitude in the brainstem neural response was greater when the stimulus was band-pass filtered between 2 and 4 kHz as compared to when the stimulus was band-pass filtered between 4 and 6 kHz, low-pass filtered at 2 kHz or presented in the full bandwidth condition. Last, neural phase-locking to f0 was reduced or absent in envelope FFRs measured to filtered stimuli that lacked spectral energy above 0.125 kHz or below 6 kHz. Similarly, little to no energy was seen at F1 in spectral FFRs obtained to low-, high-, or band-pass filtered stimuli that did not contain energy in the F1 region. For stimulus conditions that contained energy at F1, the strength of the peak at F1 in the spectral FFR varied little with low-, high-, or band-pass filtering. Energy at f0 in envelope FFRs may arise due to neural phase-locking to low-, mid-, or high-frequency stimulus components, provided the stimulus envelope is modulated by at least two interacting harmonics. Stronger neural responses at f0 are measured when filtering results in stimulus bandwidths that preserve stimulus energy at F1 and F2. In addition, results suggest that unresolved harmonics may favorably influence f0 strength in the neural response. Lastly, brainstem neural representation of the F1-related harmonic measured in spectral FFRs obtained to filtered stimuli is related to the presence or absence of stimulus energy at F1. These findings add to the existing literature exploring the viability of the FFR as an objective technique to evaluate hearing aid fitting where stimulus bandwidth is altered by design due to frequency-specific gain applied by amplification algorithms.

A Digital Filtering Method for Eliminating DC Offset in Ambulatory ECG Signals

The amplifier is easy to saturation because of polarization voltage in ambulatory ECG acquisition. The traditional way is using analog high-pass filter to eliminate, but the output tends to have a residue. If upgrading high-pass filter cutoff frequency, it will lead to low frequency distortion of ECG signals. In this paper, a Savitzky-Golay (SG) smoothing filter has been designed by combining the single edge point M and the polynomial order p, which can fit the polarization voltage components of ECG signals, filter useful components and get drift-free ECG signals by using the subtraction algorithm. The results of ECG filtering experiment verify the feasibility of the SG smoothing filter, and show the filtered ECG signal without any losses of useful components.

Fast time-varying linear filters for suppression of baseline drift in electrocardiographic signals

BackgroundThe paper presents a method of linear time-varying filtering, with extremely low computational costs, for the suppression of baseline drift in electrocardiographic (ECG) signals. An ECG signal is not periodic as the length of its heart cycles vary. In order to optimally suppress baseline drift by the use of a linear filter, we need a high-pass filter with time-varying cut-off frequency controlled by instant heart rate.MethodsRealization of the high-pass (HP) filter is based on a narrow-band low-pass (LP) filter of which output is subtracted from the delayed input. The base of an LP filter is an extremely low computational cost Lynn’s filter with rectangular impulse response. The optimal cut-off frequency of an HP filter for baseline wander suppression is identical to an instantaneous heart rate. Instantaneous length of heart cycles (e.g. RR intervals) are interpolated between QRS complexes to smoothly control cut-off frequency of the HP filter that has been used.Results and conclusionsWe proved that a 0.5 dB decrease in transfer function, at a time-varying cut-off frequency of HP filter controlled by an instant heart rate, is acceptable when related to maximum error due to filtering. Presented in the article are the algorithms that enable the realization of time-variable filters with very low computational costs. We propose fast linear HP filters for the suppression of baseline wander with time-varying cut-off frequencies controlled by instant heart rate. The filters fulfil accepted professional standards and increase the efficiency of the noise suppression.

Wide Frequency Band Active Damping Strategy for DFIG System High Frequency Resonance

As a popular renewable power generation solution, the Doubly Fed Induction Generator (DFIG)-based wind power system may suffer from High Frequency Resonance (HFR) caused by the impedance interaction between the DFIG system and the parallel compensated weak network. A wide frequency band active damping strategy for DFIG system HFR, including a high-pass filter and a virtual resistance, is proposed in this paper. The advantages of this active damping strategy are: 1) no resonance frequency detection unit is required; thus the control complexity can be decreased; and 2) no active damping parameters adjustment is needed within certain wide frequency band; thus the robustness of the proposed active damping strategy can be improved. The parameter design of the high-pass filter cutoff frequency and the virtual resistance are theoretically analyzed with the purpose of satisfactory active damping. A 7.5-kW down-scaled experimental setup is built up for the experimental validation of the proposed active damping method.

A 1µs Settling Time Fully Digital AGC System with a 1GHz-Bandwidth Variable Gain Amplifier for WiGig/IEEE802.11ad Multi-Gigabit Wireless Transceivers

This paper presents an automatic gain control (AGC) system suitable for 60GHz direct conversion receivers. By using a two step gain control algorithm with high-pass filter cutoff frequency switching, the proposed AGC system realizes fast settling time and wide dynamic range simultaneously. The paper also discusses wide-bandwidth variable gain amplifier (VGA) design. By introducing digitally-controlled resistors and gain flattening capacitors, the proposed VGA realizes wide gain range while compensating gain variations due to parasitic capacitance of MOS switches. The AGC system is implemented in a transceiver chipset where RFIC and BBIC are fabricated in 90nm CMOS and 40nm CMOS respectively. The measurement shows excellent dynamic range of 47dB with +/-1dB gain accuracy within 1µs settling time, which satisfies the stringent requirements of the IEEE802.11ad standard.

Characterization of crackles from patients with fibrosis, heart failure and pneumonia

The spectral analysis of crackles sounds has been carried out based on the assumption that they are stationary signals, and the majority of the work on the crackles was accomplished before the publication of the Computerized Respiratory Sound Analysis (CORSA) guidelines.This works characterizes crackles acquired from patients with fibrosis, heart failure, and pneumonia, breathing at a constant rate, with a system developed according to the CORSA guidelines. Their maximum frequency was obtained by applying discrete pseudo Wigner-Ville distribution, suitable for non-stationary signals, and an objective method to estimate the maximum frequency, the modified geometric method. The effects of the breathing rate and the tidal volume on the spectra of the crackles were also investigated. The role of the high-pass filter cutoff frequency of the acquisition system on the characteristics of the acquired crackles was also assessed in this present study. Higher high-pass filter cutoff frequency allows for higher amplification which modifies the maximum frequency and the 2CD index. It is shown that the crackles acquired according to the CORSA guidelines have higher frequencies and shorter 2CD indexes than those previously reported, highlighting the need for the standardization and detailed report of the acquisition setup when quantifying lung sounds.The results pointed out that the maximum frequency and the 2CD indexes may allow crackles generated by fibrosis to be distinguished from the ones generated by the heart failure and pneumonia. It is not possible, however, by means of these two indexes, to differentiate between pneumonia and heart failure crackles.

Psychophysical tuning curves and recognition of highpass and lowpass filtered speech for a person with an inverted V-shaped audiogram.

A single subject whose audiogram resembled an inverted V shape (good hearing at 4000 Hz, poorer hearing at other frequencies) was tested. Results of the TEN(HL) test suggested that a dead region (DR) in the cochlea was present at all test frequencies from 500 to 3000 Hz, but no DR was present at 4000 Hz. Psychophysical tuning curves obtained using signal frequencies of 2000, 3000, 4000, and 6000 Hz showed upward shifted tips for the lowest two signal frequencies and a downward shifted tip for the highest frequency. The results suggested a functioning region extending from 3900 to 5100 Hz, with DRs outside that range. The identification of nonsense syllables, amplified according to the Cambridge formula, was measured as a function of lowpass or highpass filter cutoff frequency. The results suggested that useful speech information could only be extracted from a limited frequency range around 4000 Hz.

Psychophysical tuning curves and recognition of highpass and lowpass filtered speech for a person with an inverted V-shaped audiogram

A single subject whose audiogram resembled an inverted V shape (good hearing at 4000 Hz, and poorer hearing at other frequencies was tested. Results of the threshold-equalizing noise test suggested that a dead region (DR) in the cochlea was present at all test frequencies from 500 to 3000 Hz, but no DR was present at 4000 Hz. Psychophysical tuning curves (PTCs) obtained using signal frequencies of 2000, 3000, 4000, and 6000 Hz showed upward shifted tips for the lowest two signal frequencies, and a downward shifted tip for the highest frequency. The results of the PTCs suggested a functioning region extending from 3900 to 5100 Hz, with DRs outside that range. The identification of nonsense syllables, amplified according to the "Cambridge formula," was measured as a function of lowpass or highpass filter cutoff frequency. The results suggested that useful speech information could only be extracted from a limited frequency range around 4000 Hz.

Blood Pressure Simulation using an Arterial Pressure-volume Model

Using an arterial pressure-volume (APV) model, we performed an analysis of the conventional blood pressure estimation method using an oscillometric sphygmomanometer with computer simulation. Traditionally, the maximum amplitude algorithm (MAA) has been applied to the oscillation waveforms of the APV model to obtain the mean arterial pressure and the characteristic ratio. The estimation of mean arterial pressure and characteristic ratio was significantly affected by the shape of the blood pressure waveforms and the cutoff frequency of high-pass filter (HPF) circuitry. Experimental errors result from these effects when estimating blood pressure. To determine an algorithm independent of the influence of waveform shapes and parameters of HPF, the volume oscillation of the APV model and the phase shift of the oscillation with fast Fourier transform (FFT) were tested while increasing the cuff pressure from 1 mmHg to 200 mmHg (1 mmHg/s). The phase shift between ranges of volume oscillation was then only observed between the systolic and the diastolic blood pressures. The same results were obtained from simulations performed on two different arterial blood pressure waveforms and one hyperthermia waveform.

Speech recognition as a function of high-pass filter cutoff frequency for people with and without low-frequency cochlear dead regions

Regions in the cochlea with no (or very few) functioning inner hair cells and/or neurons are called "dead regions" (DRs). The recognition of high-pass filtered nonsense syllables was measured as a function of filter cutoff frequency for hearing-impaired people with and without low-frequency (apical) cochlear DRs. The diagnosis of any DR was made using the TEN(HL) test, and psychophysical tuning curves were used to define the edge frequency (f(e)) more precisely. Stimuli were amplified differently for each ear, using the "Cambridge formula." For subjects with low-frequency hearing loss but without DRs, scores were high (about 78%) for low cutoff frequencies, remained approximately constant for cutoff frequencies up to 862 Hz, and then worsened with increasing cutoff frequency. For subjects with low-frequency DRs, performance was typically poor for the lowest cutoff frequency (100 Hz), improved as the cutoff frequency was increased to about 0.57f(e), and worsened with further increases. These results indicate that people with low-frequency DRs are able to make effective use of frequency components that fall in the range 0.57f(e) to f(e), but that frequency components below 0.57f(e) have deleterious effects. The results have implications for the fitting of hearing aids to people with low-frequency DRs.

Discrimination of first- and second-order regular intervals from random intervals as a function of high-pass filter cutoff frequency

This study extends the work of Kaernbach and Demany [J. Acoust. Soc. Am. 104, 2998–2306 (1998)] in which regular interval stimuli (RIS) click trains with first-order intervals could be discriminated from random-interval click trains, but RIS with second-order intervals could not. Kaernbach and Demany concluded that their results cast doubt on autocorrelation as a method of analysis for such stimuli. The present study investigated the same stimuli, but for a variety of filter conditions. The results suggest that while RIS click trains with first-order intervals are more easily discriminated from random-interval stimuli than second-order interval RIS click trains, discrimination based on second-order intervals is possible except when the stimuli are high-pass filtered above 8 kHz, i.e., above the spectral region of phase locking.

MfERG waveform characteristics in the RS1h mouse model featuring a 'negative' ERG.

Several retinal disorders lead to a relatively greater attenuation of the b-wave compared to the a-wave of the electroretinogram (ERG), a constellation called 'negative' ERG. To determine the waveform characteristics of multifocal ERGs (mfERGs) and their dependence on recording parameters in such a case, we studied the Rs1h(-/Y) mouse, the model for x-linked juvenile retinoschisis. mfERGs were recorded with a VERIS 4 system connected to a piggyback stimulator prototype that added the stimulus to the optical pathway of a HRA scanning-laser ophthalmoscope (SLO) by means of a wavelength-sensitive mirror. Real-time fundus visualization was achieved with the infrared laser of the SLO (835 nm). High-pass filter settings and the time interval used by the 'artefact removal' feature were varied to study their influence on the waveform. The mfERG in the Rs1h(-/Y) mouse had a 'negative' shape. However, the high-pass filter setting had to be lowered from the usual 10 Hz down to about 2 Hz in order to obtain that result, otherwise the negative shape was lost and mainly a positive peak remained. Similarly, a short time interval used by the 'artefact removal' feature also removed the negative shape. The Rs1h(-/Y) mouse was found to be a valuable model of diseases with a 'negative' waveform shape also in mfERG. Our results underline the importance of a lower high-pass filter cutoff frequency when recording mfERGs in such disorders. In addition, if the 'artefact removal' feature is used, it should be verified that it doesn't distort the waveform shape.

The effect of interval order and highpass filtering on the pitch strength of shuffled click-train regular interval stimuli

Regular interval stimuli (RIS) contain temporal regularities that are known to produce a pitch percept. Previous experiments [Mapes-Riordan and Yost, ARO MidWinter meeting proceedings (2000)] showed that shuffled, wide-band first-order ‘‘kxkx’’ click-train RIS have a stronger pitch strength than the original, unshuffled stimuli, where ‘‘k’’ is a fixed duration interval and ‘‘x’’ is a random interval. The primary difference between ordered and shuffled click-train sequences is that shuffled sequences contain multiple instances of regular ‘‘k’’ intervals. This result provides evidence for the importance of the short-term periodicity within RIS in determining its pitch strength. The current experiments investigated whether this phenomenon also occurred when the RIS were created from higher-order intervals and/or whose spectrum was limited to unresolved frequency channels. A set of trials was run in which listeners compared the pitch strength of an ordered click-train RIS and a shuffled version of the same sequence. Relative pitch strength judgments were made as a function of the regular interval duration, regular interval order, and highpass filter cutoff frequency. The results of these experiments revealed that second-order interval click-train RIS require resolved frequency components to generate a salient pitch percept. [Work supported by a NIDCD Program Project Grant.]

Magnitude estimation of degraded speech quality by normal- and impaired-hearing listeners.

Speech quality magnitude estimates (SQME's) were obtained from 12 sensorineurally impaired-hearing listeners on connected speech samples degraded by changing low-pass filter cutoff frequency, high-pass filter cutoff frequency, or percent total harmonic distortion (THD) by linear rectification. Log SQME's varied linearly with log bandwidth for filtered signals and with log percent undegraded (100-% THD) for linearly rectified signals. Significant variations were found among the slopes of the log-log functions for degradation modes and group-by-degradation mode interactions. Slope differences appeared to represent differential sensitivity of the listeners to changes in mode and degree of degradation. The findings are sufficiently encouraging to suggest that direct scaling procedures be employed in future studies of the evaluation of communication systems and the perception of complex signals.