Effects Of Automatic Gain Control Research Articles

The Effects of an ADC on SCR Improvement

This paper presents a closed form expression for estimating the signal-to-clutter improvement of a digital signal processor. The expression is unique in that it combines a number of factors (analog-to-digital converter dynamic range, phase noise, integration gain, automatic gain control effects, and clutter filter specifications) that have historically been treated separately. Two standard cases are shown as subsets of the general expression: signal-to-clutter improvement for analog signal processors and moving target indicator-type digital signal processors.

Acoustic temporal modulation detection and speech perception in cochlear implant listeners

The goals of the present study were to measure acoustic temporal modulation transfer functions (TMTFs) in cochlear implant listeners and examine the relationship between modulation detection and speech recognition abilities. The effects of automatic gain control, presentation level and number of channels on modulation detection thresholds (MDTs) were examined using the listeners' clinical sound processor. The general form of the TMTF was low-pass, consistent with previous studies. The operation of automatic gain control had no effect on MDTs when the stimuli were presented at 65 dBA. MDTs were not dependent on the presentation levels (ranging from 50 to 75 dBA) nor on the number of channels. Significant correlations were found between MDTs and speech recognition scores. The rates of decay of the TMTFs were predictive of speech recognition abilities. Spectral-ripple discrimination was evaluated to examine the relationship between temporal and spectral envelope sensitivities. No correlations were found between the two measures, and 56% of the variance in speech recognition was predicted jointly by the two tasks. The present study suggests that temporal modulation detection measured with the sound processor can serve as a useful measure of the ability of clinical sound processing strategies to deliver clinically pertinent temporal information.

EyeTap Devices for Augmented, Deliberately Diminished, or Otherwise Altered Visual Perception of Rigid Planar Patches of Real-World Scenes

Diminished reality is as important as augmented reality, and both are possible with a device called the Reality Mediator. Over the past two decades, we have designed, built, worn, and tested many different embodiments of this device in the context of wearable computing. Incorporated into the Reality Mediator is an “EyeTap” system, which is a device that quantifies and resynthesizes light that would otherwise pass through one or both lenses of the eye(s) of a wearer. The functional principles of EyeTap devices are discussed, in detail. The EyeTap diverts into a spatial measurement system at least a portion of light that would otherwise pass through the center of projection of at least one lens of an eye of a wearer. The Reality Mediator has at least one mode of operation in which it reconstructs these rays of light, under the control of a wearable computer system. The computer system then uses new results in algebraic projective geometry and comparametric equations to perform head tracking, as well as to track motion of rigid planar patches present in the scene. We describe how our tracking algorithm allows an EyeTap to alter the light from a particular portion of the scene to give rise to a computer-controlled, selectively mediated reality. An important difference between mediated reality and augmented reality includes the ability to not just augment but also deliberately diminish or otherwise alter the visual perception of reality. For example, diminished reality allows additional information to be inserted without causing the user to experience information overload. Our tracking algorithm also takes into account the effects of automatic gain control, by performing motion estimation in both spatial as well as tonal motion coordinates.

The effect of automatic gain control on serial, matched-filter acquisition in direct-sequence packet radio communications

The performance of a noncoherent serial acquisition technique is evaluated for direct-sequence spread-spectrum packet communications. The acquisition technique that is considered uses threshold crossing of a matched-filter output to detect a fixed-length preamble at the start of each packet. The analysis accounts for frequency mismatch between the transmitter and the receiver due to oscillator inaccuracies and mobility-induced Doppler shifts. It also accounts for the effects of automatic gain control (AGC) in the receiver. The role of the AGC system in determining the acquisition performance is examined. In addition, selection of the optimal acquisition threshold is considered, and a simple method for selection of a good suboptimal threshold is presented. It is shown that use of this threshold results in performance close to that obtained with the optimal threshold over a wide range of channels.

Objective Speech Quality Estimation for Analog Mobile Channels: Problems and Solutions

This article describes an objective speech quality assessment method developed for the Hungarian NMT-450 cellular mobile telephone system. The method is based on a psychoacoustic front end followed by a cognitive modeling component. Special problems of the NMT system, such as handover (HOV), the effects of automatic gain control (AGC), and the intrusion of signaling noise, are addressed in the cognitive module. Correlation between the subjective and objective quality measures is maximized by finding a transformation that linearizes their relationship. A correlation of 0.95 is achieved on an independent test set between the subjective speech quality and the proposed objective quality measure.

The Effect of Automatic Gain Control in Hearing-Impaired Listeners with Different Dynamic Ranges

The purpose of this study was to evaluate the effect of Automatic Gain Control (AGC) on the speech perception of hearing-impaired listeners with varying degrees of reduced dynamic range. Linearly amplified and AGC recordings of the CUNY-Nonsense Syllable Test (CUNY-NST) were constructed in quiet and in noise. They were presented to 30 subjects with flat to gradually sloping sensorineural hearing loss separated into three groups of ten by mean width of dynamic range for puretones. Analysis of the CUNY-NST scores revealed that: (1) AGC significantly improved speech perception in quiet for the subjects with narrower dynamic ranges; (2) the improvement in speech perception with AGC in quiet was dependent upon the manner of articulation of the stimulus; (3) consonant confusions in quiet for AGC were more often due to place errors compared to the linear condition which may be a reflection of a reduction in distinctive feature errors; and (4) linear amplification resulted in higher CUNY-NST scores than did AGC in the presence of back-ground noise.

Comments on "Effects of Automatic Gain Control on Phase-Locked Loop Behavior in the Presence of Interference"

Comments on "Effects of Automatic Gain Control on Phase-Locked Loop Behavior in the Presence of Interference"

Effects of Automatic Gain Control on Phase-Locked Loop Behavior in the Presence of Interference

The behavior of a second-order phase-locked loop (PLL) in the presence of an interfering signal has been analyzed by different authors with different results. The discrepancy is attributed to the presence or absence of an automatic gain controlled amplifier preceeding the PLL. Simulation results verify that the presence of the automatic gain controlled amplifier reduces the tendency of the PLL to break lock from the desired signal in favor of the interfering signal