DIGITAL VOICE SWITCH WITH AN ADAPTIVE DIGITALLY-CONTROLLED THRESHOLD

• US 3,832,491 A
• Filed: 02/13/1973
• Issued: 08/27/1974
• Est. Priority Date: 02/13/1973
• Status: Expired due to Term

• Current Assignee: Joseph Albert Sciulli, Paul Andrew Lutz
• Original Assignee: Joseph Albert Sciulli, Paul Andrew Lutz
• Inventors: Sciulli, Joseph Albert, Lutz, Paul Andrew
• Primary Examiner(s): Claffy, Kathleen
• Assistant Examiner(s): Leaheey, Jon Bradford
• Application Number:
  US05/331,735
• Time in Patent Office: 560 Days
• Field of Search: 179/1VC,15AS,1SA
• US Class Current: 704/212
• CPC Class Codes: G10L 25/78 Detection of presence or absence of voice signals switching of direction of transmission by voice frequency in two-way loud-speaking telephone systems H04M9/10

Abstract

A voice switch for connecting voice PCM samples in a channel to an output line, said switch comprising a digital adaptive threshold generating means. The threshold level, against which voice samples are compared, is varied in accordance with the loudness of the talker by comparing the number of times the threshold is exceeded over a given period with a reference number. A variable minimum threshold level is also provided at a level just above the channel noise level.

Claims

1. A voice switch comprising:

a. means for storing a value Representing a threshold level, b. threshold detector means for providing an output threshold signal each time a voice sample applied thereto exceeds a threshold level applied thereto, c. means for connecting said value stored in said storing means to said threshold detector means, d. means for connecting periodic samples of a signal on a channel adapted to carry voice signals to said threshold detector, e. accumulator means for accumulating over a predetermined period of time a number representing the number of times said voice samples exceed said threshold value, f. adder means having first and second inputs for adding the values applied to said first and second inputs and providing the sum at an output, said first input being connected to the output of said storing means, g. first comparison means for comparing said accumulated number with a first number and for providing a value representing a positive increment to the second input of said adder means when said accumulated number is greater than said first number, h. second comparison means for comparing said accumulated number with a second number and providing a value representing a negative increment to said second input of said adder means when said accumulated number is less than said second number, and i. means responsive to the output from said adder and to maximum and minimum threshold levels for entering the output sum into said storing means if said output sum is between said maximum and minimum threshold levels.

2. A voice as claimed in claim 1 wherein said voice samples are digitally encoded samples of said signal on a channel adapted to carry voice signals.

3. A voice switch as claimed in claim 1 wherein said negative increment is greater in magnitude than said positive increment.

4. A voice switch as claimed in claim 1 wherein said maximum and minimum threshold values are fixed values.

5. A voice switch as claimed in claim 1 wherein said minimum value is generated by an adaptive minimum threshold level generating means comprising, a. second storage means for storing a value representing said minimum threshold level, and b. means for varying said value in said second storage means to maintain said minimum threshold level at a value a small increment above the noise level in said channel.

6. A voice switch as claimed in claim 5 wherein said means for varying said value in said second storage means comprises, a. a second adder means, having first and second inputs and an output, for providing a sum of the values applied to said first and second inputs at said output, said output being connected to the input of said second storage means, and said first input being connected to the output of said second storage means, b. means connected to said first and second comparison means for detecting a lack of change in said threshold level for a fixed number of said periods, and c. means responsive to the detection by said detection means for applying a value representing a positive increment to the second input of said second adder means.

7. A voice switch as claimed in claim 6 wherein said means for varying said value in said second storage means further comprises, a. means responsive to said minimum threshold level for forming a third threshold level a small incremental amount less than said minimum threshold level, b. second detecting means responsive to said voice samples and said third threshold level for providing a signal output when said third threshold level is above the noise level on said channel for a fixed duration of talker inactivity, said fixed duration being a multiple of said periods, and c. means responsive to said signal output from said detecting means for applying a value representing a small negative increment to the second input of said second adder means.

8. A voice switch as claimed in claim 7 wherein said second detecting means comprises, a. second threshold detector means, Connected to receive said voice samples and said third threshold level, for providing an output threshold signal each time any said voice sample exceeds said third threshold level, b. counter means for accumulating said last mentioned output threshold signals over said given period and for providing an overflow output signal during each said given period when the number of said output threshold signals exceeds a predetermined minimum number, said predetermined minimim number being substantially less than the number of said output signals expected during a said given period when said channel carries voice signals, and c. detector means connected to receive said overflow signals for providing an output signal when said detector means fails to receive any overflow signals for a predetermined number of said given periods in succession.

9. A voice switch as claimed in claim 8 wherein said voice samples are digitally encoded samples of said signal on a channel adapted to carry voice signals and all said means are adapted to handle digital signals.

10. A voice switch as claimed in claim 9 wherein said negative increment provided by said second comparison means has a greater magnitude than said positive increment provided by said first comparison means.