Comfort noise generation for digital communication systems

• US 5,630,016 A
• Filed: 03/07/1996
• Issued: 05/13/1997
• Est. Priority Date: 05/28/1992
• Status: Expired due to Term

• Current Assignee: Hughes Network Systems LLC (Echostar Corporation)
• Original Assignee: Hughes Electronics Corporation (Rtx Corporation)
• Inventors: McCarthy, Brian M., Swaminathan, Kumar
• Primary Examiner(s): MacDonald, Allen R.
• Assistant Examiner(s): Sartori, Michael A.
• Application Number:
  US08/614,777
• Time in Patent Office: 432 Days
• Field of Search: 395/2, 395/2.1, 395/2.23, 395/2.24, 395/2.28, 395/2.29, 395/2.32, 395/2.35, 395/2.36, 395/2.37, 381/36, 381/40, 381/47, 379/58.59, 455/50.1, 455/51.1, 455/51.2, 455/52.1, 455/63, 455/67.3, 455/222, 455/296, 455/297
• US Class Current: 704/228
• CPC Class Codes: G10L 19/012 Comfort noise or silence coding

Abstract

A digital discontinuous cellular communication system has a transmitter that transmits two frames of data following detection of voice inactivity. A receiver includes a comfort noise generator that uses the two frames of data to output noise to the speaker during period of voice inactivity. The comfort noise generator includes synthesis codebook with samples scaled by actual background noise and excitation codebook with samples filtered and scaled by the background noise that are combined to produce comfort noise having attributes and loudness level of the received background noise prior to interruption of transmission. The scaled signals are weighted to vary the loudness level and spectral attributes.

Claims

1. A method of generating background noise during voice inactivity intervals in a communication system having a transmitter with an encoder for encoding and transmitting audio data, and a receiver remote from the transmitter with a decoder for receiving and decoding the transmitted audio data, said method comprising the steps of:

encoding audio data in the transmitter and transmitting the encoded audio data to the receiver;

detecting in the transmitter voice activity and voice inactivity;

continuing transmission of encoded audio data during a predetermined time interval following each detection of voice inactivity;

discontinuing transmission of encoded audio data at the expiration of each of said predetermined time intervals;

resuming transmission of encoded audio data upon detection in the transmitter of voice activity;

decoding in the remote receiver the encoded audio data received from the transmitter;

detecting in the remote receiver voice activity and voice inactivity at the transmitter;

processing in the receiver the decoded audio data including data received during each of said predetermined time intervals after the detection of voice inactivity in the transmitter, said processing step further comprising the steps of;

deriving a first series of output signals corresponding to an average loudness level of received noise;

deriving a second series of output signals having spectral shape attributes corresponding to the received noise; and

combining the first and second series of derived signals to generate audible analog audio of varying loudness level representing background noise;

wherein the deriving of the first and second series of signals includes weighting each of the first and second series of signals successively to vary the loudness level and spectral shape during periods of voice inactivity, the weighting of each of the first and second series of signals comprising multiplying each of the first series of signals by a first weighting factor and each of the second series of signals by a second weighting factor, the first and second weighting factors being varied to vary the loudness level and spectral shape;

wherein the weighting each of the first and second series of signals successively includes repeatedly incrementing the value of the first weighting factor in steps from a minimum value to a maximum value and then decrementing the value of the first weighting factor from the maximum value to the minimum value; and

repeatedly generating audible analog audio representing background noise based upon the audio data processed during each of said predetermined time intervals until the resumption of transmission of the encoded audio data.

2. The method of claim 1, wherein the value of the first weighting factor is repeatedly incremented in at least ten steps at a rate of one step per sixty-four signals from zero to one and then decremented from one to zero at said rate.

3. A system for generating comfort noise for a digital communication system during a period of voice inactivity immediately following a period of voice activity based on received data representing background noise during said period of voice activity, comprising:

a synthesis codebook having a first table of values corresponding to long term estimates of background noise;

an excitation codebook having a second table of values corresponding to long term estimates of spectrally flattened background noise;

means including the received data during each said period of voice inactivity and values from the first table of synthesis codebook for producing a first series of signals having a loudness level averaged over a plurality of frames of data;

means including the received data during said period of voice inactivity and the second table of values from the excitation codebook for producing a second series of signals having spectral shape attributes corresponding to the received data; and

means for combining the first and second series of signals to generate the background noise of varying amplitude during said period of voice inactivity,

wherein the means for producing the first and second series of signals includes means for weighting each of the signals of the first and second series of signals, using a first and a second weighting factor, respectively, to vary the spectral shape and loudness level of the background noise, and

wherein the value of the first weighting factor is repeatedly incremented in steps from a minimum value to a maximum value and then decremented from the maximum value to the minimum value.