Audio coder/decoder with predictive coding of synthesis filter and critically-sampled time aliasing of prediction domain frames

1. An audio encoding apparatus adapted for encoding frames of a sampled audio signal to obtain encoded frames, wherein a frame comprises a number of time domain audio samples, comprising:

a predictive coding analysis stage for determining information on coefficients of a synthesis filter and a prediction domain frame based on a frame of audio samples;

a time-aliasing introducing transformer for transforming overlapping prediction domain frames to a frequency domain to obtain prediction domain frame spectra, wherein the time-aliasing introducing transformer is adapted for transforming the overlapping prediction domain frames in a critically-sampled way; and

a redundancy reducing encoder for encoding the prediction domain frame spectra to obtain the encoded frames based on the coefficients and encoded prediction domain frame spectra,

a codebook encoder for encoding the prediction domain frames based on a predetermined codebook to obtain a codebook encoded prediction domain frame; and

a decider for deciding whether to use a codebook encoded prediction domain frame or an encoded prediction domain frame to obtain a finally encoded frame based on a coding efficiency measure.

wherein at least one of the predictive coding analysis stage, the time-aliasing introducing transformer, the redundancy reducing encoder, the codebook encoder, and the decider comprises a hardware implementation.

2. The audio encoding apparatus of claim 1 , wherein a prediction domain frame is based on an excitation frame comprising samples of an excitation signal for the synthesis filter.

3. The audio encoding apparatus of claim 1 , wherein the time-aliasing introducing transformer is adapted for transforming overlapping prediction domain frames such that an average number of samples of a prediction domain frame spectrum equals the average number of samples in a prediction domain frame.

4. The audio encoding apparatus of claim 1 , wherein the time-aliasing introducing transformer is adapted for transforming overlapping prediction domain frames according to a modified discrete cosine transform (MDCT).

5. The audio encoding apparatus of claim 1 , wherein the time-aliasing introducing transformer comprises a windowing filter for applying a windowing function to overlapping prediction domain frames and a converter for converting windowed overlapping prediction domain frames to the prediction domain frame spectra.

6. The audio encoding apparatus of claim 5 , wherein the time-aliasing introducing transformer comprises a processor for detecting an event and for providing a window sequence information if the event is detected and wherein the windowing filter is adapted for applying the windowing function according to the window sequence information.

7. The audio encoding apparatus of claim 6 , wherein the window sequence information comprises a first zero part, a second bypass part and a third zero part.

8. The audio encoding apparatus of claim 7 , wherein the window sequence information comprises a rising edge part between the first zero part and the second bypass part and a falling edge part between the second bypass part and the third zero part.

9. The audio encoding apparatus of claim 8 , wherein the second bypass part comprises a sequence of ones for not modifying the samples of the prediction domain frame spectra.

10. The audio encoding apparatus of claim 1 , wherein the predictive coding analysis stage is adapted for determining the information on the coefficients based on linear predictive coding (LPC).

11. The audio encoding apparatus of claim 1 , further comprising a switch coupled to the decider for switching the prediction domain frames between the time-aliasing introducing transformer and the codebook encoder based on the coding efficiency measure.

12. A method for encoding frames of a sampled audio signal to obtain encoded frames, wherein a frame comprises a number of time domain audio samples, comprising

determining, by a predictive coding analysis stage, information on coefficients for a synthesis filter based on a frame of audio samples and determining a prediction domain frame based on the frame of audio samples;

transforming, by a time-aliasing introducing transformer, overlapping prediction domain frames to a frequency domain to obtain prediction domain frame spectra in a critically-sampled way introducing time aliasing;

encoding, by a redundancy reducing encoder, the prediction domain frame spectra to obtain the encoded frames based on the coefficients and encoded prediction domain frame spectra;

encoding, by a codebook encoder, the prediction domain frames based on a predetermined codebook to obtain a codebook encoded prediction domain frame; and

deciding, by a decider, whether to use a codebook encoded prediction domain frame or an encoded prediction domain frame to obtain a finally encoded frame based on a coding efficiency measure

wherein at least one of the predictive coding analysis stage, the time-aliasing introducing transformer, the redundancy reducing encoder, the codebook encoder, and the decider comprises a hardware implementation.

13. A non-transitory storage medium having stored thereon a computer program comprising a program code for performing the method for encoding frames of a sampled audio signal to obtain encoded frames, wherein a frame comprises a number of time domain audio samples, the method comprising

determining information on coefficients for a synthesis filter based on a frame of audio samples;

determining a prediction domain frame based on the frame of audio samples;

transforming overlapping prediction domain frames to the frequency domain to obtain prediction domain frame spectra in a critically-sampled way introducing time aliasing; and

encoding the prediction domain frame spectra to obtain the encoded frames based on the coefficients and the encoded prediction domain frame spectra,

encoding the prediction domain frames based on a predetermined codebook to obtain a codebook encoded prediction domain frame; and

deciding whether to use a codebook encoded prediction domain frame or an encoded prediction domain frame to obtain a finally encoded frame based on a coding efficiency measure,

when the program code runs on a computer or processor.

14. An audio decoding apparatus for decoding encoded frames to obtain frames of a sampled audio signal, wherein a frame comprises a number of time domain audio samples, comprising:

a redundancy retrieving decoder for decoding the encoded frames to obtain an information on coefficients for a synthesis filter and prediction domain frame spectra;

an inverse time-aliasing introducing transformer for transforming the prediction domain frame spectra to the time domain to obtain overlapping prediction domain frames, wherein the inverse time-aliasing introducing transformer is adapted for determining overlapping prediction domain frames from consecutive prediction domain frame spectra, wherein the inverse time-aliasing introducing transformer further comprises a converter for converting prediction domain frame spectra to converted overlapping prediction domain frames and a windowing filter for applying a windowing function to the converted overlapping prediction domain frames to obtain the overlapping prediction domain frames, wherein the inverse time-aliasing introducing transformer comprises a processor for detecting an event and for providing a window sequence information if the event is detected to the windowing filter and wherein the windowing filter is adapted for applying the windowing function according to the window sequence information, and wherein the window sequence information comprises a first zero part, a second bypass part and a third zero part;

an overlap/add combiner for combining overlapping prediction domain frames to obtain a prediction domain frame in a critically-sampled way; and

a predictive synthesis stage for determining the frames of audio samples based on the coefficients and the prediction domain frame,

wherein at least one of the redundancy retrieving decoder, the inverse time-aliasing introducing transformer, the overlap/add combiner, and the predictive analysis stage comprises a hardware implementation.

15. The audio decoding apparatus of claim 14 , wherein the overlap/add combiner is adapted for combining overlapping prediction domain frames such that an average number of samples in a prediction domain frame equals an average number of samples in a prediction domain frame spectrum.

16. The audio decoding apparatus of claim 14 , wherein the inverse time-aliasing introducing transformer is adapted for transforming the prediction domain frame spectra to the time domain according to an inverse modified discrete cosine transform (IMDCT).

17. The audio decoding apparatus of claim 14 , wherein the predictive synthesis stage is adapted for determining a frame of audio samples based on linear prediction coding (LPC).

18. The audio decoding apparatus of claim 14 , wherein the window sequence further comprises a rising edge part between the first zero part and the second bypass part and a falling edge part between the second bypass part and the third zero part.

19. The audio decoding apparatus of claim 18 , wherein the second bypass part comprises a sequence of ones for modifying the samples of the prediction domain frame.

20. A method for decoding encoded frames to obtain frames of a sampled audio signal, wherein a frame comprises a number of time domain audio samples, comprising decoding, by a redundancy retrieving decoder, the encoded frames to obtain an information on coefficients for a synthesis filter and prediction domain frame spectra;

transforming, by the inverse time-aliasing introducing transformer, the prediction domain frame spectra to the time domain to obtain overlapping prediction domain frames from consecutive prediction domain frame spectra, wherein the transforming comprises:

converting prediction domain frame spectra to converted overlapping prediction domain frames,

applying a windowing function, by a windowing filter, to the converted overlapping prediction domain frames to obtain the overlapping prediction domain frames,

detecting an event, and providing a window sequence information if the event is detected to the windowing filter,

wherein the windowing filter is adapted for applying the windowing function according to the window sequence information, and

wherein the window sequence information comprises a first zero part, a second bypass part and a third zero part;

combining, by an overlap/add combiner, overlapping prediction domain frames to obtain a prediction domain frame in a critically sampled way; and

determining, by a predictive analysis stage, the frame based on the coefficients and the prediction domain frame,

wherein at least one of the redundancy retrieving decoder, the inverse time-aliasing introducing transformer, the overlap/add combiner, and the predictive analysis stage comprises a hardware implementation.

21. A non-transitory storage medium having stored thereon a computer program product for performing the method for decoding encoded frames to obtain frames of a sampled audio signal, wherein a frame comprises a number of time domain audio samples, the method comprising

decoding the encoded frames to obtain an information on coefficients for a synthesis filter and prediction domain frame spectra;

transforming the prediction domain frame spectra to the time domain to obtain overlapping prediction domain frames from consecutive prediction domain frame spectra, wherein the transforming comprises

converting prediction domain frame spectra to converted overlapping prediction domain frames,

applying a windowing function, by a windowing filter, to the converted overlapping prediction domain frames to obtain the overlapping prediction domain frames,

detecting an event, and providing a window sequence information if the event is detected to the windowing filter,

wherein the windowing filter is adapted for applying the windowing function according to the window sequence information, and

wherein the window sequence information comprises a first zero part, a second bypass part and a third zero part;

combining overlapping prediction domain frames to obtain a prediction domain frame in a critically sampled way; and

determining the frame based on the coefficients and the prediction domain frame,

when the computer program runs on a computer or processor.