A Two-Step Adaptive Noise Cancellation System for Dental-Drill Noise Reduction

This paper introduces a two-step dental-drill Noise Reduction (NR) technique based upon the Adaptive Noise Cancellation (ANC) system. The proposed technique is particularly designed for the NR headphone, which the patients should be wearing while having their dental treatment. In the first step, a tone-frequency extraction algorithm is proposed to estimate the main sinusoidal frequency of the dental-drill noise. The estimated sinusoidal signal is therefore removed significantly from the dental-drill noise by the use of the ANC system. Then, by using another ANC system and a high-pass filter in the second step, the residual high-frequency components of the dental-drill noise are eliminated sufficiently. Computer simulations based on recorded dental-drill sounds and real speech signals demonstrate the efficiency of the proposed two-step ANC system for dental-drill noise reduction, both in terms of the noise attenuation performance and the speech quality of the enhanced speech signal, as compared to the conventional two-microphone ANC system under ideal situation. Moreover, results of a subjective listening test with 15 listeners are also given to guarantee satisfied speech quality of the enhanced speech signal employing the proposed two-step dental-drill NR technique

Active Control of Aerodynamic Feedback Noise from a Small Step on a Backward-facing Step

In order to reduce an aerodynamic tonal noise from a rear-view mirror, active control technique with oscillating jets was utilized. Since the aerodynamic tonal noise of rear-view mirror was generated by a small perturbation caused by a small step on a surface of the rear-view mirror, oscillating jets were introduced to break it. Wind tunnel experiments were conducted to measure aerodynamic sound and flow fields around the two dimensional backward-facing step. The experimental results showed that the noise reduction level depended on the frequency and intensity of the oscillating jets. The noise reduction level was over 20 dB at the oscillation frequency about 400Hz and the amplitude of the jet about 0.1 m/s. Both of the frequency and intensity of the jet were smaller than the frequency of the feedback noise (2 kHz) and the velocity of the uniform flow (30 m/s). These results indicated that the oscillating jets effectively reduced aerodynamic noise with small amount of energy

Design techniques for low-power SAR ADCs in nano-scale CMOS technologies

This thesis presents low power design techniques for successive approximation register (SAR) analog-to-digital converters (ADCs) in nano-scale CMOS technologies. Low power SAR ADCs face two major challenges especially at high resolutions: (1) increased comparator power to suppress the noise, and (2) increased DAC switching energy due to the large DAC size. To improve the comparator’s power efficiency, a statistical estimation based comparator noise reduction technique is presented. It allows a low power and noisy comparator to achieve high signal-to-noise ratio (SNR) by estimating the conversion residue. A first prototype ADC in 65nm CMOS has been developed to validate the proposed noise reduction technique. It achieves 4.5 fJ/conv-step Walden figure of merit and 64.5 dB signal-to-noise and distortion ratio (SNDR). In addition, a bidirectional single-side switching technique is developed to reduce the DAC switching power. It can reduce the DAC switching power and the total number of unit capacitors by 86% and 75%, respectively. A second prototype ADC with the proposed switching technique is designed and fabricated in 180nm CMOS technology. It achieves an SNDR of 63.4 dB and consumes only 24 Wat 1MS/s, leading to aWalden figure of merit of 19.9 fJ/conv-step. This thesis also presents an improved loop-unrolled SAR ADC, which works at high frequency with reduced SAR logic power and delay. It employs the bidirectional single-side switching technique to reduce the comparator common-mode voltage variation. In addition, it uses a Vcm-adaptive offset calibration technique which can accurately calibrate comparator’s offset at its operating Vcm. A prototype ADC designed in 40nm CMOS achieves 35 dB at 700 MS/s sampling rate and consumes only 0.95 mW, leading to a Walden figure of merit of 30 fJ/conv-step.Electrical and Computer Engineerin

Material decomposition for dual-energy propagation-based phase-contrast CT

Material decomposition refers to using the energy dependence of material physical properties to differentiate materials in a sample, which is a very important application in computed tomography(CT). In propagation-based X-ray phase-contrast CT, the phase retrieval and Reconstruction are always independent. Moreover, like in conventional CT, the material decomposition methods in this technique can be classified into two types based on pre-reconstruction and post-reconstruction (two-step). The CT images often suffer from noise and artifacts in those methods because of no feedback and correction from the intensity data. This work investigates an iterative method to obtain material decomposition directly from the intensity data in different energies, which means that we perform phase retrieval, reconstruction and material decomposition in a one step. Fresnel diffraction is applied to forward propagation and CT images interact with this intensity data throughout the iterative process. Experiments results demonstrate that compared with two-step methods, the proposed method is superior in accurate material decomposition and noise reduction

Aerodynamic noise from rigid trailing edges with finite porous extensions

This paper investigates the effects of finite flat porous extensions to semi-infinite impermeable flat plates in an attempt to control trailing-edge noise through bio-inspired adaptations. Specifically the problem of sound generated by a gust convecting in uniform mean steady flow scattering off the trailing edge and permeable-impermeable junction is considered. This setup supposes that any realistic trailing-edge adaptation to a blade would be sufficiently small so that the turbulent boundary layer encapsulates both the porous edge and the permeable-impermeable junction, and therefore the interaction of acoustics generated at these two discontinuous boundaries is important. The acoustic problem is tackled analytically through use of the Wiener-Hopf method. A two-dimensional matrix Wiener-Hopf problem arises due to the two interaction points (the trailing edge and the permeable-impermeable junction). This paper discusses a new iterative method for solving this matrix Wiener-Hopf equation which extends to further two-dimensional problems in particular those involving analytic terms that exponentially grow in the upper or lower half planes. This method is an extension of the commonly used "pole removal" technique and avoids the needs for full matrix factorisation. Convergence of this iterative method to an exact solution is shown to be particularly fast when terms neglected in the second step are formally smaller than all other terms retained. The final acoustic solution highlights the effects of the permeable-impermeable junction on the generated noise, in particular how this junction affects the far-field noise generated by high-frequency gusts by creating an interference to typical trailing-edge scattering. This effect results in partially porous plates predicting a lower noise reduction than fully porous plates when compared to fully impermeable plates.Comment: LaTeX, 20 pp., 19 graphics in 6 figure

Status report on a natural laminar-flow nacelle flight experiment

The natural laminar flow (NLF) nacelle experiment is part of a drag reduction production program, and has the dual objectives of studying the extent of NLF on full scale nacelles in a flight environment and the effect of acoustic disturbance on the location of transition on the nacelle surface. The experiment is being conducted in two phases: (1) an NLF fairing was flown on a full scale Citation nacelle to develop the experiment technique and establish feasibility; (2) full scale, flow through, NLF nacelles located below the right wing of an experimental NASA OV-1 aircraft are evaluated. The measurements of most interest are the static pressure distribution and transition location on the nacelle surface, and the fluctuating pressure levels associated with the noise sources. Data are collected in combinations of acoustic frequencies and sound pressure levels. The results of phase 2 tests to date indicate that on shape GE2, natural laminar flow was maintained as far aft as the afterbody joint at 50 percent of the nacelle length. An aft facing step at this joint caused premature transition at this station. No change was observed in the transition pattern when the noise sources were operated

Comparison of Speech Enhancement Algorithms

The simplest and very familiar method to take out stationary background noise is spectral subtraction. In this algorithm, a spectral noise bias is calculated from segments of speech inactivity and is subtracted from noisy speech spectral amplitude, retaining the phase as it is. Secondary procedures follow spectral subtraction to reduce the unpleasant auditory effects due to spectral error. The drawback of spectral subtraction is that it is applicable to speech corrupted by stationary noise. The research in this topic aims at studying the spectral subtraction & Wiener filter technique when the speech is degraded by non-stationary noise. We have studied both algorithms assuming stationary noise scenario. In this we want to study these two algorithms in the context of non-stationary noise. Next, decision directed (DD) approach, is used to estimate the time varying noise spectrum which resulted in better performance in terms of intelligibility and reduced musical noise. However, the a priori SNR estimator of the current frame relies on the estimated speech spectrum from the earlier frame. The undesirable consequence is that the gain function doesn’t match the current frame, resulting in a bias which causes annoying echoing effect. A method called Two-step noise reduction (TSNR) algorithm was used to solve the problem which tracks instantaneously the non-stationarity of the signal but, not by losing the advantage of the DD approach. The a priori SNR estimation was modified and made better by an additional step for removing the bias, thus eliminating reverberation effect. The output obtained even with TSNR still suffers from harmonic distortions which are inherent to all short time noise suppression techniques, the main reason being the inaccuracy in estimating PSD in single channel systems. To outdo this problem, a concept called, Harmonic Regeneration Noise Reduction (HRNR) is used wherein a non-linearity is made use of for regenerating the distorted/missing harmonics. All the above discussed algorithms have been implemented and their performance evaluated using both subjective and objective criteria. The performance is significantly improved by using HRNR combined with TSNR, as compared to TSNR, DD alone, as HRNR ensures restoration of harmonics. The spectral subtraction performance stands much below the above discussed methods for obvious reasons

Comparison of Speech Enhancement Algorithms

AbstractThe simplest and very familiar method to take out stationary background noise is spectral subtraction. In this algorithm, a spectral noise bias is calculated from segments of speech inactivity and is subtracted from noisy speech spectral amplitude, retaining the phase as it is. Secondary procedures follow spectral subtraction to reduce the unpleasant auditory effects due to spectral error. The drawback of spectral subtraction is that it is applicable to speech corrupted by stationary noise. The research in this topic aims at studying the spectral subtraction & Wiener filter technique when the speech is degraded by non-stationary noise. We have studied both algorithms assuming stationary noise scenario. In this we want to study these two algorithms in the context of non-stationary noise. Next, decision directed (DD) approach, is used to estimate the time varying noise spectrum which resulted in better performance in terms of intelligibility and reduced musical noise. However, the a priori SNR estimator of the current frame relies on the estimated speech spectrum from the earlier frame. The undesirable consequence is that the gain function doesn’t match the current frame, resulting in a bias which causes annoying echoing effect. A method called Two-step noise reduction (TSNR) algorithm was used to solve the problem which tracks instantaneously the non-stationarity of the signal but, not by losing the advantage of the DD approach. The a priori SNR estimation was modified and made better by an additional step for removing the bias, thus eliminating reverberation effect. The output obtained even with TSNR still suffers from harmonic distortions which are inherent to all short time noise suppression techniques, the main reason being the inaccuracy in estimating PSD in single channel systems. To outdo this problem, a concept called, Harmonic Regeneration Noise Reduction (HRNR) is used wherein a non-linearity is made use of for regenerating the distorted/missing harmonics. All the above discussed algorithms have been implemented and their performance evaluated using both subjective and objective criteria. The performance is significantly improved by using HRNR combined with TSNR, as compared to TSNR, DD alone, as HRNR ensures restoration of harmonics. The spectral subtraction performance stands much below the above discussed methods for obvious reasons

Reduction of Uncertainty in Bolus Transit Time Measurement in Quantitative Fluorescence Angiography

During cerebral revascularization surgeries, blood flow values help surgeons to monitor the quality of the pro- cedure, e.g., to avoid cerebral hyperperfusion syndrome due to excessively enhanced perfusion. The state-of-the-art technique is the ultrasonic flow probe that has to be placed around the blood vessel. This causes contact between probe and vessel, which, in the worst case, leads to rupture. The recently developed intraoperative indocyanine green (ICG) Quantitative Fluorescence Angiography (QFA) is an alternative technique that overcomes this risk. However, it has been shown by the developer that the calculated flow has deviations. After determining the bolus transit time as the most sensitive parameter in flow calculation, we propose a new two-step uncertainty reduction method for flow calculation. The first step is to generate more data in each measurement that results in functions of the parameters. Noise can then be reduced in a second step. Two methods for this step are compared. The first method fits the model for each parameter function separately and calculates flow from models, while the second one fits multiple parameter functions together. The latter method is proven to perform best by in silico tests. Besides, this method reduces the deviation of flow comparing to original QFA as expected. Our approach can be generally used in all QFA applications using two-point theory. Further development is possible if number of dimensions of the achieved parameter data are broadened that results in even more data for processing in the second step

Mitigating Modal Noise in Multimode Circular Fibres by Optical Agitation using a Galvanometer

© 2024 The Author(s). Published by Oxford University Press on behalf of Royal Astronomical Society. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY), https://creativecommons.org/licenses/by/4.0/Modal noise appears due to the non-uniform and unstable distribution of light intensity among the finite number of modes in multimode fibres. It is an important limiting factor in measuring radial velocity precisely by fibre-fed high-resolution spectrographs. The problem can become particularly severe as the fibre's core become smaller and the number of modes that can propagate reduces. Thus, mitigating modal noise in relatively small core fibres still remains a challenge. We present here a novel technique to suppress modal noise. Two movable mirrors in the form of a galvanometer reimage the mode-pattern of an input fibre to an output fibre. The mixing of modes coupled to the output fibre can be controlled by the movement of mirrors applying two sinusoidal signals through a voltage generator. We test the technique for four multimode circular fibres: 10 and 50 micron step-index, 50 micron graded-index, and a combination of 50 micron graded-index and 5:1 tapered fibres (GI50t). We present the results of mode suppression both in terms of the direct image of the output fibre and spectrum of white light obtained with the high-resolution spectrograph. We found that the galvanometer mitigated modal noise in all the tested fibres, but was most useful for smaller core fibres. However, there is a trade-off between the modal noise reduction and light-loss. The GI50t provides the best result with about 60% mitigation of modal noise at a cost of about 5% output light-loss. Our solution is easy to use and can be implemented in fibre-fed spectrographs.Peer reviewe