Method and apparatus for encoding speech

1. A method, comprising:

receiving, in an encoder, a speech signal including voice signals and background signals;

detecting voice activity and providing an indicator when no voice activity is detected;

encoding the speech signal to generate a plurality of parameters representing the signal, the plurality of parameters comprising a linear prediction calculation vector of quantized linear prediction filter coefficients, a gain parameter based on open-loop lag value, and a residual vector; and

when the indicator is not present, outputting a first parametric representation of the speech signal comprising the plurality of parameters, and, when the indicator is present, modifying at least one of the plurality of parameters and outputting a second parametric representation of the speech signal including the modified parameter.

2. The method according to claim 1 , wherein the modifying the at least one parameter comprises modifying a value utilized in the generation of the parameter, whereby modification of that value produces a modified parameter.

3. The method according to claim 2 , wherein the modifying the value comprises randomizing the value.

4. The method according to claim 1 , wherein the modifying the at least one parameter comprises taking into account the energy levels associated with the parameter.

5. The method according to claim 1 , wherein the speech signal is received as a sequence of samples arranged in frames.

6. The method according to claim 5 , wherein the modifying the at least one parameter comprises smoothing the parameter for a current frame based on characteristics of the parameter in other frames of the speech signal.

7. The method according to claim 6 , wherein said other frames include adjacent frames.

8. The method according to claim 6 , wherein the modifying the at least one parameter comprises producing a count of the number of received frames up to a predetermined maximum, and using said count in the modifying step.

9. The method according to claim 1 , wherein the modifying the at least one parameter comprises generating a randomized value for the parameter.

10. An apparatus, comprising:

receiving means for receiving a speech signal including voice signals and background signals;

detecting means for detecting voice activity and providing an indicator when no voice activity is detected;

encoding means for encoding the speech signal to generate a plurality of parameters representing the signal, the plurality of parameters comprising a linear prediction calculation vector of quantized linear prediction filter coefficients, a gain parameter based on open-loop lag value, and a residual vector; and

outputting means for, when said indicator is not present, outputting a first parametric representation of the speech signal comprising said plurality of parameters, and, when the indicator is present, modifying at least one of the parameters and outputting a second parametric representation of the speech signal including the modified parameter.

11. A computer readable medium storing a computer program which, when executed, encodes speech by implementing a method, the method comprising:

receiving, in an encoder, a speech signal including voice signals and background signals;

detecting voice activity and providing an indicator when no voice activity is detected;

encoding the speech signal to generate a plurality of parameters representing the signal, the plurality of parameters comprising a linear prediction calculation vector of quantized linear prediction filter coefficients, a gain parameter based on open-loop lag value, and a residual vector; and

when the indicator is not present, outputting a first parametric representation of the speech signal comprising the plurality of parameters, and, when the indicator is present, modifying at least one of the plurality of parameters and outputting a second parametric representation of the speech signal including the modified parameter.

12. A system, comprising:

an input unit which receives a speech signal including voice signals and background signals;

a voice activity detector which detects voice activity and to provide an indicator when no voice activity is detected;

an encoder which encodes the speech signal to generate a plurality of parameters representing the signal, the plurality of parameters comprising a linear prediction calculation vector of quantized linear prediction filter coefficients, a gain parameter based on open-loop lag value, and a residual vector;

a modifying unit which modifies, when the indicator is present at least one of the parameters; and

an output unit which outputs, when the indicator is not present, a first parametric representation comprising said plurality of parameters, and to which outputs a second parametric representation of the speech signal when the indicator is present, the second parametric representation comprising the modified parameter.

13. An apparatus, comprising:

an input which receives a speech signal including voice signals and background signals;

a voice activity detector which detects voice activity and to provide an indicator when no voice activity is detected;

an encoder which encodes the speech signal to generate a plurality of parameters representing the signal, the plurality of parameters comprising of a linear prediction calculation vector of quantized linear prediction filter coefficients, a gain parameter based on open-loop lag value, and a residual vector;

modifying circuitry which modifies, when the indicator is present, at least one parameter of the plurality of parameters; and

an output which outputs a first parametric representation of the speech signal when the indicator is not present, the first parametric representation comprising the plurality of parameters, and which outputs a second parametric representation of the speech signal when the indicator is present, the second parametric representation comprising the modified parameter.

14. The apparatus according to claim 13 , wherein the input is receives the speech signal as a sequence of samples arranged in frames, and wherein the modifying circuitry is configured to smooth the parameter for a current frame based on characteristics of the parameter in other frames of the speech signal.

15. The apparatus according to claim 13 , wherein the input is receives the speech signal as a sequence of samples arranged in frames, and wherein the modifying circuitry is produces a count of the number of received frames to a predetermined maximum, and is configured to use the count in the modifying the parameter.

16. The apparatus according to claim 13 , wherein the modifying circuitry is generates a randomized value for the parameter.

17. The apparatus according to claim 13 wherein the modifying circuitry is takes into account energy levels associated with the parameter.

18. A network entity, comprising:

an input which receives a speech signal including voice signals and background signals;

a voice activity detector which detects voice activity and to provide an indicator when no voice activity is detected;

an encoder which encodes the speech signal to generate a plurality of parameters representing the signal, the plurality of parameters comprising a linear prediction calculation vector of quantized linear prediction filter coefficients, a gain parameter based on open-loop lag value, and a residual vector;

modifying circuitry which modifies, when the indicator is present, at least one parameter of the plurality of parameters; and

an output which outputs a first parametric representation of the speech signal when the indicator is not present, the first parametric representation comprising the plurality of parameters, and which outputs a second parametric representation of the speech signal when the indicator is present, the second parametric representation comprising the modified parameter.

19. The network entity according to claim 18 , which comprises a mobile terminal.