Method and apparatus for obtaining spectrum coefficients for a replacement frame of an audio signal, audio decoder, audio receiver, and system for transmitting audio signals

Patent metadata

Field	Value
Publication number	US-9916834-B2
Application number	US-201514977207-A
Country	US
Kind code	B2
Filing date	Dec 21, 2015
Priority date	Jun 21, 2013
Publication date	Mar 13, 2018
Grant date	Mar 13, 2018

Abstract

An approach is described that obtains spectrum coefficients for a replacement frame of an audio signal. A tonal component of a spectrum of an audio signal is detected based on a peak that exists in the spectra of frames preceding a replacement frame. For the tonal component of the spectrum a spectrum coefficients for the peak and its surrounding in the spectrum of the replacement frame is predicted, and for the non-tonal component of the spectrum a non-predicted spectrum coefficient for the replacement frame or a corresponding spectrum coefficient of a frame preceding the replacement frame is used.

First claim

The invention claimed is:

1. A method for acquiring spectrum coefficients for a replacement frame of an audio signal, the method comprising:
detecting a tonal component of a spectrum of an audio signal based on a peak that exists in the spectra of frames preceding a replacement frame;
for the tonal component of the spectrum, predicting spectrum coefficients for the peak and its surrounding in the spectrum of the replacement frame;
for the non-tonal component of the spectrum, selecting the non-tonal component from the list consisting of a non-predicted spectrum coefficient for the replacement frame and a corresponding spectrum coefficient of a frame preceding the replacement frame,
wherein the spectrum coefficients for the peak and its surrounding in the spectrum of the replacement frame are predicted based on magnitudes of the complex spectrum of the second last frame preceding the replacement frame and the predicted phase of the complex spectrum of the replacement frame,
the phase of the complex spectrum of the replacement frame is predicted based on the phase of the complex spectrum of the last frame preceding the replacement frame and a phase shift between the last frame and the second last frame preceding the replacement frame, and
the phase of the complex spectrum of the last frame preceding the replacement frame is determined based on the magnitude of the complex spectrum of the second last frame preceding the replacement frame, the phase of the complex spectrum of the second last frame preceding the replacement frame, the phase shift between the last frame and the second last frame preceding the replacement frame and the real spectrum of the last frame.

2. The method of claim 1 , wherein the tonal component is defined by the peak and its surrounding.

3. The method of claim 1 , wherein the surrounding of the peak is defined by a predefined number of coefficients around the peak.

4. The method of claim 1 , wherein the surrounding of the peak comprises a first number of coefficients on the left from the peak and a second number of coefficients on the right from the peak.

5. The method of claim 4 , wherein the first number of coefficients comprises coefficients between a left foot and the peak plus the coefficient of the left foot, and wherein the second number of coefficients comprises coefficients between a right foot and the peak plus the coefficient of the right foot.

6. The method of claim 4 , wherein the first number of coefficients on the left from the peak and the second number of coefficients on the right from the peak are equal.

7. The method of claim 6 , wherein the first number of coefficients on the left from the peak is three and the second number of coefficients on the right from the peak is three.

8. The method of claim 3 , wherein the predefined number of coefficients around the peak is set prior to detecting the tonal component.

9. The method of claim 1 , wherein the size of the surrounding of the peak is adaptive.

10. The method of claim 9 , wherein the surrounding of the peak is selected such that surroundings around two peaks do not overlap.

11. The method of claim 1 ,
The phase shift between the last frame and the second last frame preceding the replacement frame is a refined phase shift, and the refined phase shift is determined based on the phase of the complex spectrum of the last frame preceding the replacement frame and the phase of the complex spectrum of the second last frame preceding the replacement frame.

12. The method of claim 11 , wherein the refinement of the phase shift is adaptive based on the number of consecutively lost frames.

13. The method of claim 12 , wherein starting from a third lost frame, a phase shift determined for a peak is used for predicting the spectral coefficients surrounding the peak.

14. The method of claim 13 , wherein for predicting the spectral coefficients in a second lost frame, a phase shift determined for the peak is used for predicting the spectral coefficients for the surrounding spectral coefficients when the phase shift in the last frame preceding the replacement frame is at most equal to a predefined threshold, and a phase shift determined for the respective surrounding spectral coefficients is used for predicting the spectral coefficients of the surrounding spectral coefficients when the phase shift in the last frame preceding the replacement frame is above the predefined threshold.

15. The method of claim 1 , wherein detecting a tonal component of the spectrum of the audio signal comprises:
searching peaks in the spectrum of the last frame preceding the replacement frame based on at least one predefined threshold;
adapting the at least one threshold;
and searching peaks in the spectrum of the second last frame preceding the replacement frame based on the at least one adapted thresholds.

16. The method of claim 15 , wherein adapting the at least one threshold comprises setting the at least one threshold for searching a peak in the second last frame preceding the replacement frame in a region around a peak found in the last frame preceding the replacement frame based on the spectrum and a spectrum envelope of the last frame preceding the replacement frame, or based on a fundamental frequency calculated from a pitch lag between frames of the audio signal.

17. The method of claim 16 , wherein the fundamental frequency is for the signal comprising the last frame preceding the replacement frame and the look-ahead of the last frame preceding the replacement frame.

18. The method of claim 17 , wherein the look-ahead of the last frame preceding the replacement frame is calculated on the encoder side using the look-ahead.

19. The method of claim 15 , wherein adapting the at least one threshold comprises setting the at least one threshold for searching a peak in the second last frame preceding the replacement frame in a region not around a peak found in the last frame preceding the replacement frame to a predefined threshold value.

20. The method of claim 1 , comprising:
determining for the replacement frame whether to apply a time domain concealment or a frequency domain concealment using the prediction of spectrum coefficients for tonal components of the audio signal.

21. The method of claim 20 , wherein the frequency domain concealment is applied in case the last frame preceding the replacement frame and the second last frame preceding the replacement frame comprise a constant pitch, or an analysis of the at least one frame preceding the replacement frame indicates that a number of tonal components in the signal exceeds a predefined threshold.

22. The method of claim 1 , wherein the frames of the audio signal are coded using MDCT.

23. The method of claim 1 , wherein a replacement frame comprises a frame that cannot be processed at an audio signal receiver, due to an error in the received data, or a frame that was lost during transmission to the audio signal receiver, or a frame not received in time at the audio signal receiver.

24. The method of claim 1 , wherein a non-predicted spectrum coefficient is generated using a noise generating method, the noise generating method including sign scrambling, or using a predefined spectrum coefficient from a memory, the memory including a look-up table.

25. A method for acquiring spectrum coefficients for a replacement frame of an audio signal, the method comprising:
detecting a tonal component of a spectrum

Assignees

• Fraunhofer Ges Forschung

Inventors

• Sukowski Janine
• Sperschneider Ralph
• Markovic Goran
• Jaegers Wolfgang
• Helmrich Christian
• Edler Bernd
• Geiger Ralf

Classifications

• G10L19/06

  Determination or coding of the spectral characteristics, e.g. of the short-term prediction coefficients · CPC title

• G10L19/005 Primary

  Correction of errors induced by the transmission channel, if related to the coding algorithm · CPC title

• G10L19/0212

  using orthogonal transformation · CPC title