Codex Corporation

About: Codex Corporation is a based out in . It is known for research contribution in the topics: Network packet & Signal. The organization has 189 authors who have published 241 publications receiving 32205 citations.

Digital filter with scaled tap coefficients

Abstract: Modem circuitry for processing data signals, featuring a digital filter whose tap coefficients are all scaled by a common factor such that the most significant bits of the filter output are indicative of the digital data.

Voice packet loss: destination vs. internodal links

Abstract: An investigation is made of voice packet loss behavior at both the destination and internodal links in a packet switched network. The fractional loss and blocking time periods for both are derived using a bivariate Markov model. The numerical results show that blocking due to the delay constraint at the destination can result in long periods of consecutive packet loss, which seriously degrade voice quality. This work indicates that the packets with excessive delay should be discarded at the internodal links, instead of blocked at the destination. The relation between the internodal link buffer size and end-to-end permissible queuing delay is established. >

Zero sensitivity properties of the digital lattice filter

Abstract: The first-order movement of zeros given small perturbations of the PARCOR coefficients in the all-zero digital lattice filter is determined analytically This is an extension of previous work characterizing sensitivity by integral spectral deviation measures, and is of interest since much is known about the perceptual effects of deviations in formant frequency location The principal insight is the role that the frequency of the zero plays in its sensitivity and a better understanding of the quite different sensitivity properties of the first and last PARCOR coefficients Comparison is made to the transversal filter structure, and further interpretation of the effect of preemphasis is given By examining individual terms of the zero sensitivity equations, an understanding may be gained of the factors responsible for large zero movements and the methods which may be used to decrease these movements As an example, a computationally simple bilinear type of transformation of the original PARCOR's to a new set of PARCOR's is proposed, which decreases the zero sensitivity at low frequency and increases it at high frequency The perceptual advantage is estimated by listening tests and spectral deviation plots to be comparable to that of preemphasis, about 2 bits/frame

Modem end of message detector

Abstract: In modem apparatus having receiver circuitry which demodulates a received carrier into a sequence of received signals and decodes each signal into a signal point drawn from a predetermined signal point alphabet, the received carrier being modulated in accordance with a sequence of signal points representing a message, that improvement having circuitry for estimating the receipt of the end of the message by testing each received signal against a predetermined end-of-message condition.