US 4,794,591 AGranted

Digital voice switch for a multi-port conference circuit

AssigneeGTE Communication Systems Corporation

InventorsJames Hoff, Arthur L. Walsh, John S. Young

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Abstract

An echo cancellation arrangement is provided for decreasing the "singing" of a connection of a large number of telephone subscribers in a conference calling arrangement. This arrangement includes a means for inserting quiet code during time when the voice samples of incoming PCM data are zero or below a predetermined minimum threshold level. This helps decrease the amount of feedback which is amplified and output through the codec/filter to the listeners through the PCM network. An attenuation arrangement is also included which decreases the level of a summed signal of a summing node of the conference circuit. This sum signal is the combination of each of the conferees' speech. Attenuation of this signal prohibits excessive coupling of amplified feedback to each of the listening conferees.

Claims9

Dependent claims

In a digital switching system, a codec/filter is connected to PCM transmit and PCM receive data streams of a CPU controlled switching network, a digital voice switch for a multi-port conference circuit comprising:

comparator means connected to said PCM transmit and to said PCM receive data streams, said comparator means operating in response to time slots of said PCM transmit and PCM receive data streams to provide a below threshold signal indicating one of said PCM time slots which are below a predetermined threshold value;
control means connected to said comparator means and to said CPU, said control means operating in response to a program signal of said CPU and to said below threshold signal to provide a PCM time slot containing quiet code;
and
means for inserting connected to said control means, to said PCM receive data stream and to said codec/filter, said means for inserting receiving said PCM time slot containing quiet code from said control means and operating in response to said PCM time slot containing quiet code to replace said PCM time slots being below said threshold level with said quiet code for transmission to said codec/filter.

1 more element

In a digital switching system, a codec/filter is connected to PCM transmit and PCM receive data streams of a CPU controlled switching network, a plurality of speaking conferees each connected to said codec/filter via a digital voice switch for a multi-port conference circuit, said digital voice switch comprising:

summing means connected between each of said plurality of conferees and a common summing node said summing means operating to produce a sum signal being a linear combination of each said conferees' speech;
amplification means connected between said common summing node and said codec/filter, said amplification means operating to increase an amplitude of said sum signal;
attenuation means connected between said codec/filter and said summing means and connected in shunt with said amplification means, said attenuation means operating in response to a control signal to decrease said amplitude of said sum signal;
comparator means connected to said PCM transmit and to said PCM receive data streams, said comparator means operating in response to data of PCM time slots of said PCM transmit and PCM receive data streams to provide an indication signal for time slots of said PCM transmit data stream being below a predetermined threshold level;
control means connected to said comparator means, to said CPU and to said attenuation means, said control means operating in response to said indication signal and to a program signal of said CPU to produce said control signal;
and
said attenuation means operating in response to said control signal to decrease said amplitude of said sum signal.

4 more elements

summing means connected between each of said plurality of conferees and a common summing node said summing means operating to produce a sum signal being a linear combination of each said conferees' speech;
amplification means connected between said common summing node and said codec/filter, said amplification means operating to increase an amplitude of said sum signal;
attenuation means connected between said codec/filter and said summing means and connected in shunt with said amplification means, said attenuation means operating in response to a control signal to decrease said amplitude of said sum signal;
comparator means connected to said PCM transmit and to said PCM receive data streams, said comparator means operating in response to data of PCM time slots of said PCM transmit and PCM receive data streams to provide an indication signal for time slots of said PCM transmit data stream being below a predetermined threshold level;
and
control means connected to said comparator means, to said CPU and to said attenuation means, said control means operating in response to said indication signal and to a program signal of said CPU to produce said control signal;
said attenuation means operating in response to said control signal to decrease said amplitude of said sum signal;
comparator means connected to said PCM transmit and to said PCM receive data streams, said comparator means operating in response to time slots of said PCM transmit and PCM receive data streams to provide a below threshold signal indicating PCM time slots which are below a predetermined threshold value;
said control means further operating in response to a program signal of said CPU and to said below threshold signal to provide a PCM time slot containing quiet code;
and
means for inserting connected to said control means, to said PCM receive data stream and to said codec/filter, said means for inserting operating in response to said PCM time slot containing quiet code to replace said PCM time slots being below said threshold level with said quiet code for transmission to said codec/flter.

8 more elements

Dependencies are inferred from the claim text.