Methods and devices for switching between sound signal coding modes at a coder and for producing target signals at a decoder

• US 7,979,271 B2
• Filed: 02/18/2005
• Issued: 07/12/2011
• Est. Priority Date: 02/18/2004
• Status: Active Grant

• Current Assignee: VoiceAge Corporation
• Original Assignee: VoiceAge Corporation
• Inventors: Bessette, Bruno
• Primary Examiner(s): Chawan; Vijay B
• Application Number:
  US10/589,035
• Publication Number:
  US 20070282603A1
• Time in Patent Office: 2,335 Days
• Field of Search: 704/219, 704/230, 704500-504, 704/200.1, 704/205, 704/229, 704/203, 375/243, 375/240.13, 375/240.16
• US Class Current: 704/219
• CPC Class Codes: G10L 19/005 Correction of errors induced by the transmission channel, if related to the coding algorithm
• CPC Class Codes: G10L 19/0208 Subband vocoders
• CPC Class Codes: G10L 19/24 Variable rate codecs, e.g. for generating different qualities using a scalable representation such as hierarchical encoding or layered encoding
• CPC Class Codes: G10L 19/265 Pre-filtering, e.g. high frequency emphasis prior to encoding
• CPC Class Codes: G10L 21/0232 Processing in the frequency domain

Abstract

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.

Claims

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.