Slow-acting System Research Articles

Perceptual Evaluation of Signal-to-Noise-Ratio-Aware Dynamic Range Compression in Hearing Aids.

Dynamic range compression is a compensation strategy commonly used in modern hearing aids. Fast-acting systems respond relatively quickly to the fluctuations in the input level. This allows for more effective compression of the dynamic range of speech and hence enhanced the audibility of its low-intensity components. However, such processing also amplifies the background noise, distorts the modulation spectra of both the speech and the background, and can reduce the output signal-to-noise ratio (SNR). Recently, May et al. proposed a novel SNR-aware compression strategy, in which the compression speed is adapted depending on whether speech is present or absent. Fast-acting compression is applied to speech-dominated time–frequency (T-F) units, while noise-dominated T-F units are processed using slow-acting compression. It has been shown that this strategy provides a similar effective compression of the speech dynamic range as conventional fast-acting compression, while introducing fewer distortions of the modulation spectrum of the background and providing an improved output SNR. In this study, this SNR-aware compression strategy was compared with conventional fast- and slow-acting compression in terms of speech intelligibility and subjective preference in a group of 17 hearing-impaired listeners with varying degree of hearing loss. The results show a speech intelligibility benefit of the SNR-aware compression strategy over the conventional slow-acting system. Furthermore, the SNR-aware approach demonstrates an increased subjective preference compared with both conventional fast- and slow-acting systems.

Dynamic Analysis of a Slow-active Suspension System Based on a Full Car Model

In this paper, a methodology for the design and evaluation of a slow-active vehicle suspension system is developed. The suspension consists of a limited bandwidth actuator in series with a passive spring; the combination being in parallel with a passive damper. An optimal multivariable controller is designed for a full car model. The controller takes the form of a linear quadratic regulator with supplementary states for added integral action. The car model is formulated as a linear lumped parameter model, comprised of five discrete rigid bodies. The three-dimensional vibratory motions of the vehicle are described in terms of seven degrees-of-freedom: bouncing, pitching and rolling motions of the sprung mass, and the bouncing motion of each unsprung mass. An integrated investigation of vehicle dynamics, roadway excitations and performance measures is developed in order to investigate the dynamic analysis and design of vehicle suspension systems and the consequences of vehicle ride quality. The ride isolation performance and road-holding qualities of the slow-active system are compared to those of a full bandwidth active suspension and a typical passive suspension system. The simulation results lead to the conclusion that the optimal control theory provides a useful mathematical tool for the design of active suspension systems. The optimally-controlled suspension designs prove to be effective in controlling vehicle vibrations, and achieve better performance than the conventional passive suspension. The slow-active systems offer significant improvements in controlling body resonances. In fact, the slow-active system tracks its full bandwidth active counterpart. The low power consumption capabilities of this type of system compared to full bandwidth active systems render it to be an attractive candidate for providing good ride qualities, with its real time implementation being promising.

Hydro-pneumatic Slow-active Suspension with Preview Control

SUMMARY In this work, the preview control problem is considered for fully active and hydro-pneumatic slow-active systems. Based on the quarter car model, linear optimal control theory is used to derive the control laws. The Pade approximation technique is used to represent the preview time resulting from a preview sensor mounted at the front bumper to measure the road irregularities ahead of the front wheels. The results for the slow-active system with preview showed that there is 15% improvement in ride comfort compared to slow-active without preview and 28.5% improvement over passive system at similar root mean square (r.m.s) dynamic tyre load and suspension working space. The performance gains are, however, lower by about 15% than those obtainable with the theoretically ideal, fully active system with preview. The power results for slow active with and without preview showed that a 2kW fixed displacement hydraulic pump is enough for full vehicle requirements.

Effect of Non-Linear Components on the Performance of a Hydro -Pneumatic Slow-Active Suspension System

In this work, the effects of component non-linearities on the ride performance of a hydro-pneumatic slow-active suspension system are studied theoretically. Based on the quarter car linear model, linear optimal control theory is used to calculate the feedback and feedforward gains. These gains are used in both linear and non-linear models with and without preview control. The Pade approximation technique is used to represent the preview time resulting from a preview sensor mounted on the vehicle front bumper to measure the road irregularities ahead of the front wheel. The results on a typical major road showed that at similar r.m.s. values of suspension working space, the non-linear slow-active system with preview provided a 28 per cent improvement in ride comfort and a 17 per cent reduction in dynamic tyre load compared with a passive system. However, the inclusion of non-linear effects of the components increases the ride comfort acceleration by 10 per cent and suspension working space by 12 per cent compared to the equivalent linear model at approximately equal values of r.m.s. dynamic tyre load.

PERFORMANCE ENHANCEMENT BY CONTROL LAW ADAPTATION IN SLOW-ACTIVE ROAD VEHICLE SUSPENSIONS

SUMMARY The paper is concerned with the possible performance improvements which can be obtained in an automotive active suspension system through the use of adaptive rather than fixed control. The study is wholly theoretical and treats a quarter-car, slow-active, electro-hydraulic-pneumatic suspension with elastic limit stops, through simulation of running at a constant speed on randomly profiled roads. The adaptation is intended to adjust the system operation according to the prevailing road roughness level. mad spectral properties being assumed average at all times. The road roughness estimation process is illustrated. The estimate is used to drive a gain scheduling adaptive scheme. Comparisons are made between adaptive slow-active systems. non-adaptive slow-active systems and a typical passive system. mainly by means of root mean square values of response variables. It is concluded that the assumptions made in such a study can exert a large influence on the nature of results obtained, giving rise to po...

Motion of chromatic stimuli: First-order or second-order?

This paper measures the minimum velocity required to discriminate the direction of motion (the lower threshold of motion—LTM) for patterns which consisted of spatial variations in luminance, chromaticity or luminance contrast in an attempt to distinguish between the underlying directionally selective mechanisms. The characteristics of these patterns can be defined as first-order/Fourier stimuli (luminance and chromatic gratings) or second-order/non-Fourier stimuli (contrast gratings or “beats”). Measurements for each pattern were made at durations ranging from 0.015 to 0.96 sec and at contrasts of 0.5 log units above detection threshold and 1.5 log units above the threshold for detecting the stationary pattern. Observers were able to discriminate the direction of motion in luminance gratings and high contrast chromatic gratings at all durations above 0.015 sec. The direction of motion of beats and low contrast chromatic gratings was indiscriminable until they had been presented for at least 0.12 sec. This was taken to indicate the existence of a fast-acting and a slow-acting system dealing with the first- and second-order patterns respectively. When defined on this basis, the chromatic stimulus acts as a first-order (luminance) pattern at high contrasts and a second-order (beat) pattern at low contrasts.

Road Vehicle Suspension System Design - a review

SUMMARY Based mainly on English language literature, information relating to the design of automobile suspension systems for ride comfort and control of wheel load variations for frequencies below body structure resonances is reviewed. The information is interpreted in the context of vehicles which travel through a wide speed range on roads of markedly differing quality, which do so carrying different loads and which are required to possess good handling qualities. Sections are devoted to describing road surfaces, modelling vehicles and setting up performance criteria, and to passive, active, semi-active and slow-active system types. Methods for deriving active system control laws are outlined. Strengths and weaknesses of the various systems are identified and their relative performance capabilities and equipment requirements are discussed. Attention is given to adaptation of the suspension or control system parameters to changing conditions. Remaining research needs are considered.