Browse Prior Art Database

ALGORITHM FOR HANDS FREE SPEAKERPHONE

IP.com Disclosure Number: IPCOM000007559D
Original Publication Date: 1995-Nov-01
Included in the Prior Art Database: 2002-Apr-05
Document File: 3 page(s) / 135K

Publishing Venue

Motorola

Related People

Z. Shwartzman: AUTHOR [+3]

Abstract

Many voice activated speakerphone circuits have been implemented in a number ofofftce and mobile radio products. Generally, the design concept used in such voice activated speakerphone circuits employs two variable attenuators, one in the transmit path and one in the receive path of the speakerphone. The two attenuators are typically controlled by a voice activated logic circuit monitoring the voice activity, and controlling the audio levels of the transmit and receive paths to allow halfduplex operation, i.e. con- versations in one direction at a time.

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MOTVROLA Technical Developments

ALGORITHM FOR HANDS FREE SPEAKERPHONE

by 2. Shwartzman, H. Claude and L. Fabian

INTRODUCTION

  Many voice activated speakerphone circuits have been implemented in a number ofofftce and mobile radio products. Generally, the design concept used in such voice activated speakerphone circuits employs two variable attenuators, one in the transmit path and one in the receive path of the speakerphone. The two attenuators are typically controlled by a voice activated logic circuit monitoring the voice activity, and controlling the audio levels of the transmit and receive paths to allow halfduplex operation, i.e. con- versations in one direction at a time.

  Switching the communication path and audio levels between transmit and receive operation is made such that the sum of the two attenuator values in the transmit and receive paths is kept approximately constant. If the sum of the attenuator values is designed to be sufficiently high, the loudspeaker can be located in close proximity to the microphone without risk of audio regeneration.

  Typically voice activated logic circuits in most speakerphone designs currently use the audio enve- lopes of the microphone and line inputs, together with complex analog comparator circuitry for gen- erating the required control function. In half-duplex operation the output ofthe logic circuit may also be used to control the PTT (as in Quasi-duplex operation).

  The aim of this arrangement is to provide a voice activated algorithm that can be implemented into a speakerphone microprocessor.

DETAILED DESCRIPTION:

  The primary task of the proposed voice activa- tion algorithm is to monitor both the line and the microphone audio input levels of the speakerphone. Based on these audio input levels, the microprocessor decides whether a user is talking via the line input

(microphone) or whether a remote user is talking, and (via the loudspeaker coupling into the micro- phone input) an audio signal is being undesirably regenerated in the speakerphone. The microprocessor and the logic circuit control the audio attenuator lev- els for the transmit and receive paths accordingly.

  The proposed algorithm requires the audio lev- els from both the line and microphone inputs to be fed into a zero-cross logic circuit as shown in Fig. 1. The speakerphone microprocessor subtracts the zero- cross count of line inputs from the zero cross count of microphone inputs at predetermined time inter- vals. The subtracted value is compared to a predetermined threshold level and a decision is made as to whether the speakerphone user is talking or the remote user's voice is being undesirably coupled into the speakerphone via the loudspeaker and...