Frequency response

About: Frequency response is a research topic. Over the lifetime, 25705 publications have been published within this topic receiving 332249 citations.

Vibrotactile frequency for encoding a speech parameter

Abstract: Frequency of vibration has not been widely used as a parameter for encoding speech‐derived information on the skin. Where it has been used, the frequencies employed have not necessarily been compatible with the capabilities of the tactile channel, and no determination was made of the information transmitted by the frequency variable, as differentiated from other parameters used simultaneously, such as duration, amplitude, and location. However, several investigators have shown that difference limens for vibration frequency may be small enough to make stimulus frequency useful in encoding a speech‐derived parameter such as the fundamental frequency of voiced speech. In the studies reported here, measurements have been made of the frequency discrimination ability of the volar forearm, using both sinusoidal and pulse waveforms. Stimulus configurations included the constant‐frequency vibrations used by other laboratories as well as frequency‐modulated (warbled) stimulus patterns. The frequency of a warbled stimulus was designed to have temporal variations analogous to those found in speech. The results suggest that it may be profitable to display the fundamental frequency of voiced speech on the skin as vibratory frequency, though it might be desirable to recode fundamental frequency into a frequency range more closely matched to the skin’s capability.

Frequency Limitations and Optimal Step Size for the Two-Point Central Difference Derivative Algorithm with Applications to Human Eye Movement Data

Abstract: There are many algorithms for calculating derivatives. The two-point central difference algorithm is the simplest. Besides simplicity, the two most important characteristics of this algorithm are accuracy and frequency response. The frequency content of the data prescribes a lower limit on the sampling rate. The smoothness and accuracy of the data determine the optimal step size. We discuss the low-pass filter characteristics of this algorithm and derive the optimal step size for two types of human eye movement data. To calculate the velocity of fast (saccadic) eye movements, the algorithm should have a cutoff frequency of 74 Hz. For typical slow (smooth pursuit) eye movements, a step size of 25 or 50 ms is optimal.

Adaptive Algorithms for the Rejection of Sinusoidal Disturbances Acting on Unknown Plants

Abstract: The rejection of periodic disturbances is a problem frequently encountered in control engineering, and in active noise and vibration control in particular. The paper presents a new adaptive algorithm for situations where the plant is unknown and may be time-varying. The approach consists in obtaining online estimates of the plant frequency response and of the disturbance parameters. The estimates are used to continuously update control parameters and cancel or minimize the effect of the disturbance. The dynamic behavior of the algorithm is analyzed using averaging theory. Averaging theory is used to approximate the nonlinear time-varying closed-loop system by a nonlinear time-invariant system. It is shown that the four-dimensional averaged system has a two-dimensional equilibrium surface, which can be divided into stable and unstable subsets. Trajectories generally converge to a stable point of the equilibrium surface, implying that the disturbance is asymptotically canceled even if the true parameters of the system are not exactly determined. Simulations, as well as extensive experiments on an active noise control testbed, illustrate the results of the analysis and demonstrate the ability of the algorithm to recover from abrupt system changes or track slowly-varying parameters. Extensions of the algorithm to systems with multiple inputs/outputs and disturbances consisting of multiple frequency components are provided.

Self-interference cancellation

Abstract: A wireless communication device includes, in part, an analog interference cancellation circuit and a controller. The analog cancellation circuit includes a multitude of delay paths each including a delay element and a variable attenuator. The controller dynamically varies the attenuation level of each of the variable attenuators in accordance with the frequency response characteristic of that attenuator to remove a portion of a self-interference signal present in a signal received by the device. The device measures the frequency response characteristic of the communication channel, used in determining the attenuation levels, via one or more preamble symbols. A second portion of the self-interference signal is removed by the device using a multitude of samples of a transmitted signal and a multitude of samples of a signal to be transmitted.