Switching between coding schemes

• US 7,876,966 B2
• Filed: 03/11/2003
• Issued: 01/25/2011
• Est. Priority Date: 03/11/2003
• Status: Active Grant

• Current Assignee: Intellectual Ventures I LLC (Intellectual Ventures LLC)
• Original Assignee: Spyder Navigations LLC (Intellectual Ventures LLC)
• Inventors: Ojanpera, Juha
• Primary Examiner(s): Chen; Wenpeng
• Application Number:
  US10/548,235
• Publication Number:
  US 20060173675A1
• Time in Patent Office: 2,877 Days
• Field of Search: 704/203, 375/240.26, 382/232
• US Class Current: 382/232
• CPC Class Codes: G10L 19/022 Blocking, i.e. grouping of samples in time; Choice of analysis windows; Overlap factoring
• CPC Class Codes: G10L 19/18 Vocoders using multiple modes
• CPC Class Codes: G10L 19/22 Mode decision, i.e. based on audio signal content versus external parameters

Abstract

Methods and units are shown for supporting a switching from a first coding scheme to a Modified Discrete Cosine Transform (MDCT) based coding scheme calculating a forward or inverse MDCT with a window (h(n)) of a first type for a respective coding frame, which satisfies constraints of perfect reconstruction. To avoid discontinuities during the switching, it is proposed that for a transient frame immediately after a switching, a sequence of windows (h₀(n),h₁(n),h₂(n)) is provided for the forward and the inverse MDCTs. The windows of the window sequence are shorter than windows of the first type. The window sequence splits the spectrum of a respective first coding frame into nearly uncorrelated spectral components when used as basis for forward MDCTs, and the second half of the last window (h₂(n)) of the sequence of windows is identical to the second half of a window of the first type.

Claims

1. A method for encoding a signal, the method comprising:

encoding, via a first encoding device, a first frame of a signal according to a first coding scheme; and

encoding, via a second encoding device, a second frame of the signal according to a modified discrete cosine transform (MDCT) coding scheme, wherein the second frame immediately follows the first frame, and wherein the encoding the second frame comprises;

defining a sequence of windows for the second frame, wherein the sequence of windows facilitates a transition between the first coding scheme and the MDCT coding scheme; and

producing spectral samples of the signal by calculating a MDCT for each window of the sequence of windows;

wherein the shape of a second window of the sequence of windows is based at least in part on a number of samples of a subframe of the second frame;

wherein a length of the second frame is an integer multiple of a length of the subframe of the second frame, and wherein the length of the subframe of the second frame is an even number of samples.

2. The method of claim 1, wherein the sequence of windows comprises a first window, the second window, and a third window.

3. The method of claim 2, wherein a second half of the third window is identical to a second half of a subsequent window defined to encode a subsequent frame of the signal according to the MDCT coding scheme.

4. The method of claim 2, wherein the second window has a shaping according to an equation:

5. The method of claim 2, wherein the second window is overlapped by the first window, and wherein the first window has a shape according to an equation:

6. The method of claim 2, wherein the second window is overlapped by the third window, and wherein the third window has a shape according to an equation:

7. The method of claim 2, wherein a length of the first and second windows corresponds to an even number of samples, and wherein the length of the third window is an integer multiple of the lengths of the first and second windows.

8. The method of claim 1, further comprising performing linear prediction analysis on the signal, wherein the linear prediction analysis produces signals to indicate the coding scheme to be used on each frame of the signal.

9. The method of claim 1, further comprising quantizing the spectral samples of the signal into a bitstream.

10. The method of claim 1, further comprising multiplexing, via a multiplexer, bitstreams produced by the first coding scheme and the second coding scheme into a single bitstream, wherein the single bitstream includes an indication of a type of coding scheme applied to each frame of the signal.

11. The method of claim 1, wherein the first coding scheme is an adaptive multi-rate wideband (AMR-WB) coding scheme.

12. A method for decoding a signal, the method comprising:

decoding, via a first decoding device, a bitstream of a first frame of a signal according to a first coding scheme; and

decoding, via a second decoding device, a bitstream of a second frame of the signal according to a modified discrete cosine transform (MDCT) coding scheme, wherein the second frame immediately follows the first frame, and wherein the decoding the second bitstream comprises;

defining a sequence of windows for the bitstream of the second frame, wherein the sequence of windows facilitates a transition between the first coding scheme and the MDCT coding scheme; and

producing samples of the signal by calculating an inverse MDCT for each window of the sequence of windows;

wherein the shape of a second window of the sequence of windows is based at least in part on a number of samples of a subframe of the second frame;

wherein a length of the second frame is an integer multiple of a length of the subframe of the second frame, and wherein the length of the subframe of the second frame is an even number of samples.

13. The method of claim 12, wherein the sequence of windows comprises a first window, the second window, and a third window.

14. The method of claim 13, wherein the second window has a shaping according to an equation:

15. The method of claim 13, wherein the second window is overlapped by the first window, and wherein the first window has a shape according to an equation:

16. The method of claim 13, wherein the second window is overlapped by the third window, and wherein the third window has a shape according to an equation:

17. The method of claim 13, wherein a length of the first and second windows corresponds to an even number of samples, and wherein the length of the third window is an integer multiple of the lengths of the first and second windows.

18. The method of claim 12, further comprising demultiplexing, via a demultiplexer, a single bitstream into a first bitstream, a second bitstream, and a third bitstream, wherein the first bitstream is received at the first decoder, wherein the second bitstream is received at the second decoder, and wherein the third bitstream indicates a type of coding scheme to be applied to each component of the first bitstream and the second bitstream.

19. The method of claim 12, wherein the first coding scheme is an adaptive multi-rate wideband (AMR-WB) coding scheme.

20. The method of claim 12, further comprising performing linear prediction synthesis on the samples of the signal, wherein the linear prediction synthesis produces a restored signal.

21. A hybrid encoding device comprising:

a first encoding device configured to encode a first frame of a signal according to a first coding scheme;

a second encoding device configured to encode a second frame of the signal according to a MDCT coding scheme, wherein the second frame immediately follows the first frame, and wherein the second encoding device is further configured to;

define a sequence of windows for the second frame, wherein the sequence of windows facilitates a transition between the first coding scheme and the MDCT coding scheme; and

produce spectral samples of the signal by calculating a MDCT for each window of the sequence of windows; and

a switch coupled to the first and second encoding devices, wherein the switch is configured to select one of the first or second encoding devices on a frame-by-frame basis according to a type of the signal;

wherein the shape of the second window is based at least in part on a number of samples of a subframe of the second frame;

wherein a length of the second frame is an integer multiple of a length of the subframe of the second frame, and wherein the length of the subframe of the second frame is an even number of samples.

22. An encoder component comprising:

a hardware module configured to encode a second frame of a signal according to a MDCT coding scheme, wherein the second frame immediately follows a first frame of the signal, and wherein the module comprises;

a first hardware component configured to define a sequence of windows for the second frame, wherein the sequence of windows facilitates a transition between a first coding scheme and the MDCT coding scheme; and

a second hardware component configured to produce spectral samples of the signal by calculating a MDCT for each window of the sequence of windows;

wherein the shape of a second window of the sequence of windows is based at least in part on a number of samples of a subframe of the second frame;

wherein a length of the second frame is an integer multiple of a length of the subframe of the second frame, and wherein the length of the subframe of the second frame is an even number of samples.

23. A hybrid decoding device comprising:

a first decoding device configured to decode a bitstream of a first frame of a signal according to a first coding scheme;

a second decoding device configured to decode a bitstream of a second frame of the signal according to a MDCT coding scheme, wherein the second frame immediately follows the first frame, and wherein the second decoding device is further configured to;

define a sequence of windows for the second coding frame, wherein the sequence of windows facilitates a transition between the first coding scheme and the MDCT coding scheme; and

produce spectral samples of the signal by calculating an inverse MDCT for each window of the sequence of windows; and

a switch coupled to the first and second decoding devices, wherein the switch is configured to select one of the first or second decoding devices on a frame-by-frame basis according to a third bitstream of the signal;

wherein the shape of a second window of the sequence of windows is based at least in part on a number of samples of a subframe of the second frame;

wherein a length of the second frame is an integer multiple of a length of the subframe of the second frame, and wherein the length of the subframe of the second frame is an even number of samples.

24. A decoder component comprising:

a hardware module configured to decode a bitstream of a second frame of a signal according to a MDCT coding scheme, wherein the second frame immediately follows a first frame of the signal, and wherein the module comprises;

a first hardware component configured to define a sequence of windows for the second frame, wherein the sequence of windows facilitates a transition between a first coding scheme and the MDCT coding scheme; and

a second hardware component configured to produce spectral samples of the signal by calculating an inverse MDCT for each window of the sequence of windows;

wherein the shape of a second window of the sequence of windows is based at least in part on a number of samples of a subframe of the second frame;

wherein a length of the second frame is an integer multiple of a length of the subframe of the second frame, and wherein the length of the subframe of the second frame is an even number of samples.

25. A coding system comprising:

a hybrid encoding device comprising;

a first encoding device configured to encode a first frame of a signal according to a first coding scheme;

a second encoding device configured to encode a second frame of the signal according to a MDCT coding scheme, wherein the second frame immediately follows the first frame, and wherein the second encoder is further configured to;

define a first sequence of windows for the second frame, wherein the first sequence of windows facilitates a transition between the first coding scheme and the MDCT coding scheme; and

produce a first plurality of spectral samples of the signal by calculating a MDCT for each window of the sequence of windows; and

a switch coupled to the first and second encoding devices, wherein the switch is configured to select one of the first or second encoders on a frame-by-frame basis according to a type of the signal; and

a hybrid decoding device comprising;

a first decoding device configured to decode a bitstream of a first frame of a signal according to a first coding scheme;

a second decoding device configured to decode a bitstream of a second frame of the signal according to a MDCT coding scheme, wherein the second frame immediately follows the first frame, and wherein the second decoding device is further configured to;

define a second sequence of windows for the second coding frame, wherein the second sequence of windows facilitates a transition between the first coding scheme and the MDCT coding scheme; and

produce a second plurality of spectral samples of the signal by calculating an inverse MDCT for each window of the sequence of windows; and

a switch coupled to the first and second decoding devices, wherein the switch is configured to select one of the first or second decoding devices on a frame-by-frame basis according to a third bitstream of the signal;

wherein the shape of a second window of the sequence of windows is based at least in part on a number of samples of a subframe of the second frame;

wherein a length of the second frame is an integer multiple of a length of the subframe of the second frame, and wherein the length of the subframe of the second frame is an even number of samples.

26. A hybrid encoding device comprising:

means for encoding a first frame of a signal according to a first coding scheme;

means for encoding a second frame of the signal according to a MDCT coding scheme, wherein the second frame immediately follows the first frame;

means for defining a sequence of windows for the second frame, wherein the sequence of windows facilitates a transition between the first coding scheme and the MDCT coding scheme;

means for producing spectral samples of the signal by calculating a MDCT for each window of the sequence of windows; and

means for selecting an encoding means on a frame-by-frame basis according to a type of the signal;

wherein the shape of a second window of the sequence of windows is based at least in part on a number of samples of a subframe of the second frame;

wherein a length of the second frame is an integer multiple of a length of the subframe of the second frame, and wherein the length of the subframe of the second frame is an even number of samples.

27. A non-transitory computer-readable medium having computer readable instructions stored thereon that, when executed by a processor, cause a computing device to:

encode a second frame of a signal according to a MDCT coding scheme, wherein the second frame immediately follows a first frame of the signal;

define a sequence of windows for the second coding frame, wherein the sequence of windows facilitates a transition between a first coding scheme and the MDCT coding scheme; and

produce spectral samples of the signal by calculating a MDCT for each window of the sequence of windows;

wherein the shape of a second window of the sequence of windows is based at least in part on a number of samples of a subframe of the second frame;

wherein a length of the second frame is an integer multiple of a length of the subframe of the second frame, and wherein the length of the subframe of the second frame is an even number of samples.