Methods and devices for switching between sound signal coding modes at a coder and for producing target signals at a decoder
View Patent ↗Methods and devices are used for switching between sound signal coding modes and for producing from a decoded target signal, an overlap-add target signal in a current frame coded according to a first mode. On a coder side, switching is at the junction between a previous frame coded according to a first coding mode and a current frame coded according to a second coding mode, a sound signal is filtered through a weighting filter to produce a weighted signal in the current frame, and a windowed zero-input response of the weighting filter is removed from the weighted signal. On a decoder side, a current frame of the target signal is first windowed, a left portion of a resulting window is skipped, and then a windowed zero-input response of the weighting filter is added to the decoded target signal to reconstruct the overlap-add target signal.
1. A method of switching from a first sound signal coding mode to a second sound signal coding mode at the junction between a previous frame coded according to the first coding mode and a current frame coded according to the second coding mode, wherein the sound signal is filtered through a weighting filter to produce, in the current frame, a weighted signal, comprising:
calculating a zero-input response of the weighting filter;
windowing the zero-input response so that said zero-input response has an amplitude monotonically decreasing to zero after a predetermined time period; and
in the current frame, removing from the weighted signal the windowed zero-input response.
2. A method of switching from a first sound signal coding mode to a second sound signal coding mode as defined in claim 1 , wherein calculating a zero-input response of the weighting filter comprises calculating a zero-input response in the weighted domain.
3. A method of switching from a first sound signal coding mode to a second sound signal coding mode as defined in claim 1 , wherein the first coding mode is an ACELP coding mode and the second coding mode is a TCX coding mode.
4. A method of switching from a first sound signal coding mode to a second sound signal coding mode as defined in claim 1 , wherein windowing the zero-input response comprises truncating said zero-input response to the predetermined time period.
5. A method of switching from a first sound signal coding mode to a second sound signal coding mode as defined in claim 1 , comprising, after the windowed zero-input response has been removed from the weighted signal, windowing the weighted signal into a TCX frame of predetermined duration.
6. A method of switching from a first sound signal coding mode to a second sound signal coding mode as defined in claim 5 , further comprising transforming into the frequency domain the weighted signal windowed into a TCX frame of predetermined duration.
7. A method of switching from a first sound signal coding mode to a second sound signal coding mode as defined in claim 1 , wherein the weighting filter is a perceptual weighting filter.
8. A device for switching from a first sound signal coding mode to a second sound signal coding mode at the junction between a previous frame coded according to the first coding mode and a current frame coded according to the second coding mode, wherein the sound signal is filtered through a weighting filter to produce, in the current frame, a weighted signal, comprising:
means for calculating a zero-input response of the weighting filter;
means for windowing the zero-input response so that said zero-input response has an amplitude monotonically decreasing to zero after a predetermined time period; and
means for removing, in the current frame, the windowed zero-input response from the weighted signal.
9. A device for switching from a first sound signal coding mode to a second sound signal coding mode at the junction between a previous frame coded according to the first coding mode and a current frame coded according to the second coding mode, wherein the sound signal is filtered through a weighting filter to produce, in the current frame, a weighted signal, comprising:
a calculator of a zero-input response of the weighting filter;
a window generator for windowing the zero-input response so that said zero-input response has an amplitude monotonically decreasing to zero after a predetermined time period; and
an adder for removing, in the current frame, the windowed zero-input response from the weighted signal.
10. A device for switching from a first sound signal coding mode to a second sound signal coding mode as defined in claim 9 , wherein the zero-input response calculator calculates a zero-input response in the weighted domain.
11. A device for switching from a first sound signal coding mode to a second sound signal coding mode as defined in claim 9 , wherein the first coding mode is an ACELP coding mode and the second coding mode is a TCX coding mode.
12. A device for switching from a first sound signal coding mode to a second sound signal coding mode as defined in claim 9 , wherein the window generator truncates the zero-input response to the predetermined time period.
13. A device for switching from a first sound signal coding mode to a second sound signal coding mode as defined in claim 9 , comprising another window generator for windowing, after the windowed zero-input response has been removed from the weighted signal, the weighted signal into a TCX frame of predetermined duration.
14. A device for switching from a first sound signal coding mode to a second sound signal coding mode as defined in claim 13 , further comprising a frequency transform module which, in operation, transforms in the frequency domain the weighted signal windowed into a TCX frame of predetermined duration.
15. A device for switching from a first sound signal coding mode to a second sound signal coding mode as defined in claim 9 , wherein the weighting filter is a perceptual weighting filter.
16. A method for producing from a decoded target signal an overlap-add target signal in a current frame coded according to a first coding mode, comprising:
windowing the decoded target signal of the current frame in a given window;
skipping a left portion of the window;
calculating a zero-input response of a weighting filter of the previous frame coded according to a second coding mode,
windowing the zero-input response so that said zero-input response has an amplitude monotonically decreasing to zero after a predetermined time period; and
adding the calculated zero-input response to the decoded target signal to reconstruct said overlap-add target signal.
17. A method for producing an overlap-add target signal as defined in claim 16 , comprising weighting the calculated zero-input response prior to windowing said calculated zero-input response.
18. A method for producing an overlap-add target signal as defined in claim 17 , wherein weighting the calculated zero-input response comprises perceptually weighting said calculated zero-input response.
19. A method for producing an overlap-add target signal as defined in claim 16 , comprising saving in a buffer a last portion of samples of the current frame.
20. A method for producing an overlap-add target signal as defined in claim 16 , wherein the windowed, calculated zero-input response has an amplitude monotonically decreasing to zero after 10 ms.
21. A device for producing from a decoded target signal an overlap-add target signal in a current frame coded according to a first coding mode, comprising:
means for windowing the decoded target signal of the current frame in a given window;
means for skipping a left portion of the window;
means for calculating a zero-input response of a weighting filter of the previous frame coded according to a second coding mode,
means for windowing the zero-input response so that said zero-input response has an amplitude monotonically decreasing to zero after a predetermined time period; and
means for adding the calculated zero-input response to the decoded target signal to reconstruct said overlap-add target signal.
22. A device for producing from a decoded target signal an overlap-add target signal in a current frame coded according to a first coding mode, comprising:
a first window generator for windowing the decoded target signal of the current frame in a given window;
means for skipping a left portion of the window;
a calculator of a zero-input response of a weighting filter of the previous frame coded according to a second coding mode,
a second window generator for windowing the zero-input response so that said zero-input response has an amplitude monotonically decreasing to zero after a predetermined time period; and
an adder for adding the calculated zero-input response to the decoded target signal to reconstruct said overlap-add target signal.
23. A device for producing an overlap-add target signal as defined in claim 22 , comprising a filter for weighting the calculated zero-input response prior to windowing said calculated zero-input response.
24. A device for producing an overlap-add target signal as defined in claim 23 , wherein the weighting filter is a perceptual weighting filter.
25. A device for producing an overlap-add target signal as defined in claim 22 , comprising a buffer for saving a last portion of samples of the current frame.
26. A device for producing an overlap-add target signal as defined in claim 22 , wherein the windowed, calculated zero-input response has an amplitude monotonically decreasing to zero after 10 ms.