Adaptive Frequency Prediction

• US 20100063802A1
• Filed: 09/04/2009
• Published: 03/11/2010
• Est. Priority Date: 09/06/2008
• Status: Active Grant

• Current Assignee: Huawei Technologies Co., Ltd. (Huawei Investment & Holding Co., Ltd.)
• Original Assignee: Huawei Technologies Co., Ltd. (Huawei Investment & Holding Co., Ltd.)
• Inventors: Gao, Yang
• Granted Patent: US 8,532,983 B2
• Time in Patent Office: Days
• US Class Current: 704/201
• 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 21/038 using band spreading techniques

Abstract

In one embodiment, a method of transceiving an audio signal is disclosed. The method includes providing low band spectral information having a plurality of spectrum coefficients and predicting a high band extended spectral fine structure from the low band spectral information for at least one subband, where the high band extended spectral fine structure are made of a plurality of spectrum coefficients. The predicting includes preparing the spectrum coefficients of the low band spectral information, defining prediction parameters for the high band extended spectral fine structure and index ranges of the prediction parameters, and determining possible best indices of the prediction parameters, where determining includes minimizing a prediction error between a reference subband in high band and a predicted subband that is selected and composed from an available low band. The possible best indices of the prediction parameters are transmitted.

Claims

1. A method of transceiving an audio signal, the method comprising:

providing low band spectral information comprising a plurality of spectrum coefficients;

predicting a high band extended spectral fine structure from the low band spectral information for at least one subband, the high band extended spectral fine structure comprising a plurality of spectrum coefficients, wherein predicting comprises

preparing the spectrum coefficients of the low band spectral information,

defining prediction parameters for the high band extended spectral fine structure and index ranges of the prediction parameters; and

determining possible best indices of the prediction parameters, determining comprising minimizing a prediction error between a reference subband in high band and a predicted subband that is selected and composed from an available low band; and

transmitting the possible best indices of the prediction parameters.

2. The method of claim 1, wherein the prediction parameters comprise prediction lag and sign.

3. The method of claim 1, wherein predicting comprises intra frame frequency predicting.

4. The method of claim 1, wherein the available low band is modified before predicting if a modification is performed in both an encoder and a decoder.

5. The method of claim 1, wherein minimizing the prediction error comprises minimizing the expression:

$\mathrm{Err\_F}<br><br>\left(k_p^{\mathrm{\prime <br><br>}},\mathrm{sign}\right)=\underset{k}{\sum <br><br>}<br><br><br><br>{\left[\mathrm{sign}·<br><br>{\hat{S}}_{\mathrm{LB}}<br><br>\left(k+k_p^{\mathrm{\prime <br><br>}}\right)-S_{\mathrm{ref}}<br><br>\left(k\right)\right]}^2$

by selecting best k′

_p and sign, wherein k′

_p and sign comprise prediction parameters, k′

_p comprises a prediction lag, sign comprises a value of either 1 or −

1, S_ref(·

) comprises reference coefficients of a reference subband representing ideal spectrum coefficients, and Ŝ

_LB(·

) represents the available low band.

6. The method of claim 5, wherein minimizing the prediction error further comprises maximizing the expression:

$\mathrm{Max}<br><br>\left\{\frac{{\left[\underset{k}{\sum <br><br>}<br><br><br><br>{\hat{S}}_{\mathrm{LB}}<br><br>\left(k+k_p^{\mathrm{\prime <br><br>}}\right)·<br><br>S_{\mathrm{ref}}<br><br>\left(k\right)\right]}^2}{\underset{k}{\sum <br><br>}<br><br><br><br>{\left[{\hat{S}}_{\mathrm{LB}}<br><br>\left(k+k_p^{\mathrm{\prime <br><br>}}\right)\right]}^2},\mathrm{for}<br><br><br><br>\mathrm{possible}<br><br><br><br>k_p^{\mathrm{\prime <br><br>}}\right\}$

by selecting best k′

_p and sign, wherein sign is determined by the expression;

$\begin{array}{cccc}\mathrm{If}& \underset{k}{\sum <br><br>}<br><br><br><br>{\hat{S}}_{\mathrm{LB}}<br><br>\left(k+k_p^{\mathrm{\prime <br><br>}}\right)·<br><br>S_{\mathrm{ref}}<br><br>\left(k\right)& ><br><br>=0,& \mathrm{sign}=1;<br><br>\\ \mathrm{else}& \mathrm{sign}=-1& & \end{array}$

7. The method of claim 1, further comprising receiving the possible best indices of the prediction parameters.

8. The method of claim 7, wherein an extended spectral fine structure of the at least one subband in high band is produced from the received possible best indices of the prediction parameters according to the expression:

Ŝ

_p(k)=Ŝ

_HB(k)=S_BWE(k)=S_h(k)=sign·

Ŝ

_LB(k=k′

_p)

wherein k′

_p and sign comprise prediction parameters, k′

_p comprises a prediction lag, sign comprises a value of either 1 or −

1, Ŝ

_LB(·

) represents the available low band, and Ŝ

_p(·

)=Ŝ

_HB(·

)=S_BWE(·

)=S_h(·

) comprises a predicted portion of said extended subband.

9. The method of claim 8, further comprising scaling a final energy of each predicted subband in the high band based on received spectral envelope information.

10. The method of claim 1, wherein transmitting is performed with a limited bit budget.

11. The method of claim 1, wherein transmitting comprises transmitting the possible best indices of the prediction parameters over a voice over internet protocol (VOIP) network.

12. The method of claim 1, wherein transmitting comprises transmitting the possible best indices of the prediction parameters over a voice over a mobile telephone network.

13. The method of claim 1, further comprising receiving an audio signal and converting the audio signal to the low band spectral information.

14. The method of claim 13, wherein receiving an audio signal comprises receiving a speech signal from a microphone.

15. The method of claim 1, wherein predicting is performed in a log, linear or weighted domain.

16. A method of receiving an encoded audio signal, the method comprising:

receiving the encoded audio signal, the encoded audio signal having an available low band comprising a plurality of spectrum coefficients;

predicting an extended spectral fine structure of a high band from the available low band, wherein the spectral fine structure of the high band comprises at least one subband having a plurality of spectrum coefficients, wherein predicting comprises

preparing the plurality of spectrum coefficients of the available low band,

defining prediction parameters and variation ranges of the prediction parameters based on the available low band,

estimating possible best prediction parameters based on a regularity of a harmonic structure of the available low band,

producing the extended spectral fine structure of the high band based on the estimated possible best prediction parameters of the at least one subband.

17. The method of claim 16, wherein the prediction parameters comprise a copying distance estimated by finding locations of harmonic peaks and measuring a distance between the harmonic peaks.

18. The method of claim 16, wherein the prediction parameters comprise a prediction lag estimated by maximizing a correlation between two harmonic segments in the available low band.

19. The method of claim 16, further comprising converting the extended spectral fine structure of the high band into an output audio signal.

20. The method of claim 19, wherein converting the extended spectral fine structure of the high band into an output audio signal comprises driving a loudspeaker.

21. A system for transmitting an audio signal, the system comprising:

a transmitter comprising an audio coder, the audio coder configured to;

convert the audio signal to low band spectral information comprising a plurality of spectrum coefficients,

predict a high band extended spectral fine structure from the low band spectral information for at least one subband, the high band extended spectral fine structure comprising a plurality of spectrum coefficients,

prepare the spectrum coefficients of the low band spectral information,

define prediction parameters for the high band extended spectral fine structure and index ranges of the prediction parameters,

determine possible best indices of the prediction parameters, wherein a prediction error is minimized between a reference subband in high band and a predicted subband that is selected and composed from an available low band, and

produce an encoded audio signal comprising the possible best indices of the prediction parameters;

wherein, the transmitter is configured to transmit the encoded audio signal.

22. The system of claim 21, wherein the transmitter is configured to operate over a voice over internet protocol (VOIP) system.

23. The system of claim 21, wherein the transmitter is configured to operate over a cellular telephone network.

24. The system of claim 21, further comprising a receiver configured to receive the encoded audio signal, the receiver comprising a decoder configured to produce an extended fine structure of the at least one subband based on received possible best indices of the prediction parameters.