Digital voice transmission having improved echo suppression

• US 4,652,703 A
• Filed: 03/01/1983
• Issued: 03/24/1987
• Est. Priority Date: 03/01/1983
• Status: Expired due to Term

• Current Assignee: Racal-Datacom, Inc. (Thales SA)
• Original Assignee: Racal Data Communications Incorporated
• Inventors: Miller, William J., Jayapalan, Jay P., Stephenson, Jack E., Lu, Chun C.
• Primary Examiner(s): Rubinson, Gene Z.
• Assistant Examiner(s): Vaas, R.
• Application Number:
  US06/471,137
• Time in Patent Office: 1,484 Days
• Field of Search: 179/170.2, 179/170.6, 179/170.8, 179/81 B, 179/100 L, 370/32
• US Class Current: 379/339
• CPC Class Codes: H04B 3/20 Reducing echo effects or singing; Opening or closing transmitting path; Conditioning for transmission in one direction or the other

Abstract

A digital voice communication apparatus having improved echo suppression includes a transmission gain detection circuit for detecting a near talker signal and a receiver gain detection circuit for detecting a far talker signal. An echo detecting circuit detects which of the near talker and far talker signals has a lesser value and suppresses the gain of the one detected to have the lesser value. A far talker suppressing circuit detects whether the most recent peak gain in this near talker signal is greater than a threshold and is greater than the gain of the far talker signal. If this condition exists the far talker signal is suppressed. A near talker signal suppressing circuit detects whether the most recent gain of the far talker signal is greater than a threshold and is greater than the gain of the near talker signal. If so, the gain of the near talker signal is suppressed.

Claims

1. A digital communication apparatus for transmitting and receiving a compressed digital representation of speech produced by a near talker and a far talker respectively, said compressed digital speech representation including a coded gain parameter related to speech energy, said apparatus comprising:

transmission gain detection means for reading the gain parameter of said near talker'"'"'s digital speech representation;

receiver gain detection means for reading the gain parameter of said far talker'"'"'s digital speech representation;

means for reducing the gain parameter of said far talker'"'"'s digital speech representation when a recent peak gain parameter in said near talker'"'"'s digital speech representation is greater than both (1) a first selected threshold and (2) the gain parameter of said far talker'"'"'s digital speech representation plus a selected nonzero compensation value; and

means for reducing the pain parameter of said near talker'"'"'s digital speech representation when a recent peak gain parameter in said far talker'"'"'s digital speech is greater than both (1) said first selected threshold and (2) the gain parameter of said near talker'"'"'s digital speech representation plus said selected nonzero compensation value.

2. The apparatus of claim 1, further comprising:

a near talker interrupt detection means for removing the reduction of the gain parameter of the near talker digital speech representation responsive to detecting whether the gain parameter of the near talker'"'"'s digital speech representation exceeds a second selected threshold; and

,

a far talker interrupt detection means for removing the reduction of the gain parameter of the far talker'"'"'s digital speech representation responsive to detecting whether the gain parameter of the far talker'"'"'s digital speech representation exceeds the second selected threshold.

3. A method of echo suppression in a digital communication link, said digital communication link communicating a compressed digital representation of speech produced by a near talker and a far talker, said compressed digital representation speech including a coded gain parameter related to speech energy, the method comprising the steps of:

reducing the gain parameters of said near talker or far talker digital speech representation at one end of the communication link in accordance with which of said gain parameters has the lesser magnitude;

reducing the gain parameter of said near talker or far talker digital speech representation at the other end of the communication link in accordance with which of said gain parameters has the lesser magnitude;

the reducing steps including the steps of;

reducing the gain parameters of said far talker'"'"'s digital speech representation when a recent peak gain parameter in said near talker'"'"'s digital speech representation is greater than both (1) a first selected threshold and (2) the gain parameter of said far talker'"'"'s digital speech representation plus a selected nonzero compensation value; and

reducing the gain parameter of said near talker'"'"'s digital speech representation when a recent peak gain parameter in said far talker'"'"'s digital speech representation is greater than both (1) said first selected threshold and (2) the gain parameter of said near talker'"'"'s digital speech representation plus said selected nonzero compensation value.