Apparatus and method for generating a frequency enhancement signal using an energy limitation operation

• US 9,552,823 B2
• Filed: 07/28/2015
• Issued: 01/24/2017
• Est. Priority Date: 01/29/2013
• Status: Active Grant

• Current Assignee: Fraunhofer Gesellschaft Zur Foerderung Der Angewandten Forsching E.V.
• Original Assignee: Fraunhofer Gesellschaft Zur Foerderung Der Angewandten Forsching E.V.
• Inventors: Disch, Sascha, Geiger, Ralf, Helmrich, Christian, Multrus, Markus, Schmidt, Konstantin
• Primary Examiner(s): COLUCCI, MICHAEL C
• Application Number:
  US14/811,790
• Publication Number:
  US 20150332707A1
• Time in Patent Office: 546 Days
• Field of Search: 704/205, 704/200.1, 704/222, 704/500, 704/501, 700/94
• US Class Current: 1/1
• CPC Class Codes: G10L 19/0204 using subband decomposition
• CPC Class Codes: G10L 19/032 Quantisation or dequantisation of spectral components
• CPC Class Codes: G10L 19/06 Determination or coding of the spectral characteristics, e.g. of the short-term prediction coefficients
• CPC Class Codes: G10L 19/12 the excitation function being a code excitation, e.g. in code excited linear prediction [CELP] vocoders
• CPC Class Codes: G10L 2019/0012 Smoothing of parameters of the decoder interpolation
• CPC Class Codes: G10L 2019/0016 Codebook for LPC parameters
• CPC Class Codes: G10L 21/038 using band spreading techniques
• CPC Class Codes: G10L 21/0388 Details of processing therefor
• CPC Class Codes: G10L 25/18 the extracted parameters being spectral information of each sub-band

Abstract

An apparatus for generating a frequency enhancement signal, includes: a signal generator for generating an enhancement signal from a core signal, the enhancement signal including an enhancement frequency range not included in the core signal, wherein a time portion of the enhancement signal includes subband signals for a plurality of subbands; a synthesis filterbank for generating the frequency enhanced signal using the enhancement signal, wherein the signal generator is configured for performing an energy limitation in order to make sure that the frequency enhanced signal obtained by the synthesis filterbank is so that an energy of a higher band is, at the most, equal to an energy in a lower band or is greater than an energy of a higher band, at the most, by a predefined threshold.

Claims

1. Apparatus for generating a frequency enhancement signal, comprising:

a signal generator for generating an enhancement signal from a core signal, the enhancement signal comprising an enhancement frequency range not comprised in the core signal, wherein a time portion of the enhancement signal comprises one or more subband signals for single subband or a plurality of subbands;

a synthesis filterbank for generating the frequency enhanced signal using the enhancement signal,

wherein the signal generator is configured for performing an energy limitation in order to make sure that the frequency enhanced signal acquired by the synthesis filterbank is so that an energy of a higher band is, at the most, equal to an energy in a lower band or is greater than the energy of the lower band, at the most, by a predefined threshold,

wherein the signal generator is configured to generate the plurality of subband signals of the enhancement signal by mirroring a plurality of subbands of the core signal, and

wherein the signal generator is configured to perform the mirroring based on the following equations;

Qr(t,xover+f−

1)=−

Qr(t,xover−

f);

f=1 . . . nBands

Qi(t,xover+f−

1)=Qi(t,xover−

f);

f=1 . . . nBands,

wherein Qr(t,f) is a real value of a subband signal at a time-index t and subband-index f, wherein Qi(t,f) is an imaginary value of a subband signal at a time index t and the subband index f, wherein xover is a subband referring to a crossover frequency, and wherein nBands is an integer number of bands to be reconstructed,

wherein at least one of the signal generator and the synthesis filterbank comprises a hardware implementation.

2. Apparatus of claim 1,

wherein the signal generator is configured to use, as the predefined threshold, a threshold of 3 dB or smaller or a threshold derived from a value describing a spectral distribution of energy in the core signal.

3. Apparatus of claim 1,

wherein the signal generator is configured to examine a first subband signal in a first subband, to examine a second subband signal in a second subband being adjacent in frequency to the first subband and comprising a center frequency being higher than a center frequency of the first subband, and to not limit the second subband signal, when an energy of the second subband is equal to an energy of the first subband signal or when the energy of the second subband signal is greater than the energy of the first subband signal by less than the predefined threshold.

4. Apparatus in accordance with claim 1,

wherein the signal generator is configured to perform a plurality of processing operations in a sequence, and

wherein the signal generator is configured to perform the energy limitation at an end of the sequence to acquire the enhancement signal, and

wherein the synthesis filterbank is configured to receive, as an input, the enhancement signal generated at the end of the sequence by the energy limitation.

5. Apparatus in accordance with claim 1,

wherein the signal generator is configured to perform a spectral shaping or a temporal smoothing before the energy limitation.

6. Apparatus in accordance with claim 1,

wherein the signal generator is configured to perform the limitation operation based on the following equation:

7. Apparatus of claim 6,

in which the subband comprising a lower center frequency is adjacent to the current subband.

8. Apparatus of claim 5,

wherein the signal generator is configured to perform the energy limitation with a first time resolution,

wherein the spectral shaping is performed with a second time resolution, or

wherein the temporal smoothing is performed with a third time resolution,

wherein the first time resolution is equal to the second time resolution, or wherein the third time resolution is higher than the first time resolution.

9. Apparatus of claim 1,

wherein the apparatus is configured to perform a non-guided frequency enhancement, without using parametric side information describing the enhancement frequency range not comprised in the core signal.

10. Apparatus of claim 5,

wherein the signal generator is configured to perform the spectral shaping using information on spectral centroid of a current frame in a filterbank domain.

11. Apparatus of claim 5,

wherein the signal generator is configured to perform the temporal smoothing of the plurality of subbands of the enhancement signal or the core signal using the same smoothing information calculated from the plurality of subband signals of the core signal or the enhancement signal.

12. System for processing audio signals, comprising:

an encoder for generating an encoded core signal; and

an apparatus for generating a frequency enhancement signal of claim 1,

wherein at least one of the encoder and the apparatus comprises a hardware implementation.

13. Method of generating a frequency enhancement signal, comprising:

generating, by a signal generator, an enhancement signal from a core signal, the enhancement signal comprising an enhancement frequency range not comprised in the core signal, wherein a time portion of the enhancement signal comprises one or more subband signals for a single subband or for a plurality of subbands;

generating, by a synthesis filterbank, the frequency enhanced signal using the enhancement signal,

wherein the generating comprises performing an energy limitation in order to make sure that the frequency enhanced signal acquired by the synthesis filterbank is so that an energy of a higher band is, at the most, equal to an energy in a lower band or is greater than the energy of the lower band, at the most, by a predefined threshold,

wherein the generating comprises generating the plurality of subband signals of the enhancement signal by mirroring a plurality of subbands of the core signal, and

wherein the generating comprises performing the mirroring based on the following equations;

Qr(t,xover+f−

1)=−

Qr(t,xover−

f);

f=1 . . . nBands

Qi(t,xover+f−

1)=Qi(t,xover−

f);

f=1 . . . nBands,

wherein Qr(t,f) is a real value of a subband signal at a time-index t and subband-index f, wherein Qi(t,f) is an imaginary value of a subband signal at a time index t and the subband index f, wherein xover is a subband referring to a crossover frequency, and wherein nBands is an integer number of bands to be reconstructed,

wherein at least one of the signal generator and the synthesis filterbank comprises a hardware implementation.

14. Method of processing audio signals, comprising:

generating, by an encoder, an encoded core signal; and

generating, by an apparatus, a frequency enhancement signal using a method of claim 13,

wherein at least one of the encoder and the apparatus comprises a hardware implementation.

15. A non-transitory storage medium having stored thereon a computer program for performing, when running on a computer or a processor, the method of claim 13.

16. A non-transitory storage medium having stored thereon a computer program for performing, when running on a computer or a processor, the method of claim 14.

17. Apparatus for generating a frequency enhancement signal, comprising:

a signal generator for generating an enhancement signal from a core signal, the enhancement signal comprising an enhancement frequency range not comprised in the core signal, wherein a time portion of the enhancement signal comprises one or more subband signals for single subband or a plurality of subbands;

a synthesis filterbank for generating the frequency enhanced signal using the enhancement signal,

wherein the signal generator is configured for performing an energy limitation in order to make sure that the frequency enhanced signal acquired by the synthesis filterbank is so that an energy of a higher band is, at the most, equal to an energy in a lower band or is greater than the energy of the lower band, at the most, by a predefined threshold,

wherein the signal generator is configured to perform the limitation operation based on the following equation;

18. System for processing audio signals, comprising:

an encoder for generating an encoded core signal; and

an apparatus for generating a frequency enhancement signal of claim 17,

wherein at least one of the encoder and the apparatus comprises a hardware implementation.

19. Method of generating a frequency enhancement signal, comprising:

generating, by a signal generator, an enhancement signal from a core signal, the enhancement signal comprising an enhancement frequency range not comprised in the core signal, wherein a time portion of the enhancement signal comprises one or more subband signals for a single subband or for a plurality of subbands;

generating, by a synthesis filterbank, the frequency enhanced signal using the enhancement signal,

wherein the generating comprises performing an energy limitation in order to make sure that the frequency enhanced signal acquired by the synthesis filterbank is so that an energy of a higher band is, at the most, equal to an energy in a lower band or is greater than the energy of the lower band, at the most, by a predefined threshold,

wherein the generating comprises performing the limitation operation based on the following equation;

20. A non-transitory storage medium having stored thereon a computer program for performing, when running on a computer or a processor, the method of claim 19.

21. Method of processing audio signals, comprising:

generating, by an encoder, an encoded core signal; and

generating, by an apparatus, a frequency enhancement signal using a method of claim 19,

wherein at least one of the encoder and the apparatus comprises a hardware implementation.