Browse Prior Art Database

Dynamic Level Control to Reduce Noise in Long Distance Phonemail Networking

IP.com Disclosure Number: IPCOM000035041D
Original Publication Date: 1989-May-01
Included in the Prior Art Database: 2005-Jan-28
Document File: 2 page(s) / 36K

Publishing Venue

IBM

Related People

Locke, ME: AUTHOR

Abstract

One of the major forms of distortion of voice message transmitted over the public network (analog transmission between voice messaging equipment) is additive noise. The effect of additive noise can be reduced by increasing the amplitude of the transmittal signal; however, government regulations and practical considerations do not allow transmission of signals above a certain level. This article describes the use of dynamic range compression to increase the amplitude of low amplitude parts of a message without increasing the peak amplitude of the signal in the environment described. The figure shows a diagram of the system. Target is the target message power. Alpha is a filter constant which is required to maintain stability with an imperfect transmission media (alpha is near 1).

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Dynamic Level Control to Reduce Noise in Long Distance Phonemail Networking

One of the major forms of distortion of voice message transmitted over the public network (analog transmission between voice messaging equipment) is additive noise. The effect of additive noise can be reduced by increasing the amplitude of the transmittal signal; however, government regulations and practical considerations do not allow transmission of signals above a certain level. This article describes the use of dynamic range compression to increase the amplitude of low amplitude parts of a message without increasing the peak amplitude of the signal in the environment described. The figure shows a diagram of the system. Target is the target message power. Alpha is a filter constant which is required to maintain stability with an imperfect transmission media (alpha is near 1). C is a time constant that alters how fast the feedback loop will respond to changes in the input power. Prior to message transmission, the channel loss and noise are sampled. Channel loss is measured by transmitting a test signal of a fixed power and measuring the resultant power at the receiving end. Noise power is sampled by measuring the idle channel noise (total idle channel signal power). The input is modified by a feedback loop that is designed to keep the transmitted message near a target message power. This is done by inputting positive numbers to the power filter when the output signal is less than target...