Method of transmitting speech using discontinuous transmission and comfort noise

• US 6,381,568 B1
• Filed: 05/05/1999
• Issued: 04/30/2002
• Est. Priority Date: 05/05/1999
• Status: Expired due to Fees

• Current Assignee: The United States of America As Represented By The National Security Agency
• Original Assignee: The United States of America As Represented By The Director National Security Agency
• Inventors: Supplee, Lynn Michele, Kohler, Mary A, Dean, Richard A.
• Primary Examiner(s): Dorvil, Richemond
• Application Number:
  US09/305,325
• Time in Patent Office: 1,091 Days
• Field of Search: 704/210, 704/215, 704/219, 704/200, 704/207, 704/200.1, 704/231, 704/233
• US Class Current: 704/210
• CPC Class Codes: G10L 19/012 Comfort noise or silence coding
• 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

Speech transmission method by initializing silence, transmit, and blank-period counters; receiving frame; determining frame is speech; if transmit counter is zero and blank-period counter is less than x then discard frame, increment blank-period counter, and return to second step; if transmit counter is zero, blank-period counter greater than x−1, and frame not speech then discard frame, increment blank-period counter, and return to second step; if transmit counter is zero, blank-period counter greater than x−1, and frame is speech then set transmit counter to one, set blank-period counter to zero, set silence counter to zero, encode frame, transmit encoded frame, and return to second step; if transmit counter is one, frame not speech, and silence counter less than y then encode frame, transmit encoded frame, increment silence counter, and return to second step; if transmit counter is one, frame not speech, and silence counter greater than y+z−2 then set transmit counter to zero, discard frame, encode comfort noise, transmit encoded comfort noise, increment silence counter, and return to second step; if transmit counter is one, frame not speech, and silence counter greater than y−1 then discard frame, encode comfort noise, transmit encoded comfort noise, increment silence counter, and return to second step; and if transmit counter is one, frame is speech, and silence counter less than y+z then encode frame, transmit encoded frame, set silence counter to zero, and return to second step.

Claims

1. A method of transmitting speech, comprising the steps of:

a) setting a silence counter to zero;

b) setting a transmit counter to one;

c) setting a blank period counter to zero;

d) receiving a frame of digitized information;

e) determining if the frame contains speech;

f) if the transmit counter is equal to zero and the blank period counter is less than x, where x is a positive integer, then discarding the frame, incrementing the blank period counter by one, and returning to step (d);

g) if the transmit counter is equal to zero, the blank period counter is greater than x−

1 and the frame does not contain speech then discarding the frame, incrementing the blank period counter by one, and returning to step (d);

h) if the transmit counter is equal to zero, the blank period counter is greater than x−

1, and the frame contains speech then setting the transmit counter to one, setting the blank period counter equal to zero, setting the silence counter equal to zero, encoding the frame, transmitting the encoded frame, and returning to step (d);

i) if the transmit counter is equal to one, the frame does not contain speech, and the silence counter is less than y then encoding the frame, transmitting the encoded frame, incrementing the silence counter by one, and returning to step (d);

j) if the transmit counter is equal to one, the frame does not contain speech, and the silence counter is greater than y+z−

2, where y and z are both positive integers, then setting the transmit counter to zero, discarding the frame, encoding a frame containing comfort noise, transmitting the encoded frame containing comfort noise, incrementing the silence counter by one, and returning to step (d);

k) if the transmit counter is equal to one, the frame does not contain speech, and the silence counter is greater than y−

1 then discarding the frame, encoding a frame containing comfort noise, transmitting the encoded frame containing comfort noise, incrementing the silence counter by one, and returning to step (d); and

l) if the transmit counter is equal to one, the frame contains speech, and the silence counter is less than y+z then encoding the frame, transmitting the encoded frame, setting the silence counter to zero, and returning to step (d).

2. The method of claim 1, wherein the step of discarding the frame, incrementing the blank period counter by one, and returning to step (d) if the transmit counter is equal to zero and the blank period counter is less than x is comprised of the step of discarding the frame, incrementing the blank period counter by one, and returning to step (d) if the transmit counter is equal to zero and the blank period counter is less than 2.

3. The method of claim 1, wherein said step of setting the transmit counter to zero, discarding the frame, encoding a frame containing comfort noise, transmitting the encoded frame containing comfort noise, incrementing the silence counter by one, and returning to step (d) if the transmit counter is equal to one, the frame does not contain speech, and the silence counter is greater than y+z+2 is comprised of the step of setting the transmit counter to zero, discarding the frame, encoding a frame containing comfort noise, transmitting the encoded frame containing comfort noise, incrementing the silence counter by one, and returning to step (d) if the transmit counter is equal to one, the frame does not contain speech, and the silence counter is greater than y+z+2, where y equals 3 and z equals 2.

4. The method of claim 1, wherein said step of determining if the frame contains speech is comprised of the steps of:

a) calculating an energy of the frame as

5. The method of claim 4, wherein the step of increasing the minimum energy threshold by a first user-definable percentage is comprised of the step of increasing the minimum energy threshold by one percent.

6. The method of claim 5, further including the steps of:

a) if E is less than the minimum energy threshold then setting the first user-definable percentage to what the first user-definable percentage was set to initially; and

b) if E is greater than the minimum energy threshold then increasing the first user-definable percentage by a second user-definable percentage.

7. The method of claim 6, wherein the step of if E is greater than the minimum energy threshold then increasing the user-definable percentage by a second user-definable percentage is comprised of the step of if E is greater than the minimum energy threshold then increasing the first user-definable percentage by one-hundredth of a percent.

8. The method of claim 4, further including the step of decreasing the maximum energy threshold by a third user-definable percentage.

9. The method of claim 8, wherein the step of decreasing the maximum energy threshold by a third user-definable percentage is comprised of the step of decreasing the maximum energy threshold by one percent.

10. The method of claim 9, further including the steps of:

a) if E is greater than the maximum energy threshold then setting the third user-definable percentage to what the third user-definable percentage was set to initially; and

b) if E is less than the maximum energy threshold then decreasing the third user-definable percentage by a fourth user-definable percentage.

11. The method of claim 10, wherein the step of if E is less than the maximum energy threshold then decreasing the user-definable percentage by a fourth user-definable percentage is comprised of the step of if E is less than the maximum energy threshold then decreasing the third user-definable percentage by one-hundredth of a percent.

12. The method of claim 1, wherein the step of encoding the frame in steps (h), (i), (j), (k), and (l) are each comprised of the step of encoding the frame in Mixed Excitation Linear Prediction (MELP) format.