Apparatus and method for decoding an encoded audio signal using a cross-over filter around a transition frequency

• US 10,515,652 B2
• Filed: 05/22/2018
• Issued: 12/24/2019
• Est. Priority Date: 07/22/2013
• 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, Nagel, Frederik, Neukam, Christian, Schmidt, Konstantin, Fischer, Michael
• Primary Examiner(s): Roberts, Shaun
• Application Number:
  US15/985,930
• Publication Number:
  US 20180268842A1
• Time in Patent Office: 581 Days
• Field of Search: 7042001, 704500
• CPC Class Codes: G10L 19/008 Multichannel audio signal coding or decoding using interchannel correlation to reduce redundancy, e.g. joint-stereo, intensity-coding or matrixing
• CPC Class Codes: G10L 19/02 using spectral analysis, e.g. transform vocoders or subband vocoders
• CPC Class Codes: G10L 19/0204 using subband decomposition
• CPC Class Codes: G10L 19/0208 Subband vocoders
• CPC Class Codes: G10L 19/0212 using orthogonal transformation
• CPC Class Codes: G10L 19/022 Blocking, i.e. grouping of samples in time; Choice of analysis windows; Overlap factoring
• CPC Class Codes: G10L 19/025 Detection of transients or attacks for time/frequency resolution switching
• CPC Class Codes: G10L 19/03 Spectral prediction for preventing pre-echo; Temporary noise shaping [TNS], e.g. in MPEG2 or MPEG4
• 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 21/0388 Details of processing therefor
• CPC Class Codes: G10L 25/06 the extracted parameters being correlation coefficients
• CPC Class Codes: G10L 25/18 the extracted parameters being spectral information of each sub-band
• CPC Class Codes: G10L 25/21 the extracted parameters being power information
• CPC Class Codes: H04S 1/007 in which the audio signals are in digital form data reduction aspects thereof based on psychoacoustics G10L19/02

Abstract

Apparatus for decoding an encoded audio signal including an encoded core signal, including: a core decoder for decoding the encoded core signal to obtain a decoded core signal; a tile generator for generating one or more spectral tiles having frequencies not included in the decoded core signal using a spectral portion of the decoded core signal; and a cross-over filter for spectrally cross-over filtering the decoded core signal and a first frequency tile having frequencies extending from a gap filling frequency to an upper border frequency or for spectrally cross-over filtering a first frequency tile and a second frequency tile.

Claims

1. An apparatus for decoding an encoded audio signal comprising an encoded core signal, comprising:

a core decoder for decoding the encoded core signal to acquire a decoded core signal;

a tile generator for generating one or more spectral tiles comprising frequencies not comprised by the decoded core signal using a spectral portion of the decoded core signal; and

a cross-over filter for spectrally cross-over filtering the decoded core signal and a first frequency tile comprising frequencies extending from a gap filling frequency to an upper border frequency or for spectrally cross-over filtering a first frequency tile and a second frequency tile.

2. The apparatus of claim 1,

wherein the cross-over filter is configured to perform a frequency-wise weighted addition of the decoded core signal filtered by a fade-out subfilter and at least a portion of the first frequency tile filtered by a fade-in filter within a cross-over range extending over at least three frequency values or to perform a frequency-wise weighted addition of at least a part of a first frequency tile filtered by the fade-out subfilter and at least a part of a second frequency tile filtered by the fade-in subfilter within a cross-over range extending over at least three frequency values.

3. The apparatus of claim 1,

wherein a spectral portion of the decoded core signal, a spectral portion of the first frequency tile or a spectral portion of the second frequency tile influenced by the cross-over filter is smaller than 30% of the spectral portion covered by a total spectral band of the decoded core frequency band or a total spectral band of the first or second frequency tiles and is greater than or equal to a band defined by at least 5 adjacent frequency values.

4. The apparatus of claim 1,

wherein the cross-over filter is configured for applying a cosine-like filter characteristic for fading-in and fading-out.

5. The apparatus in accordance with claim 1, comprising an envelope adjuster for envelope adjusting a cross-over filtered spectral signal in a spectral range defined by spectral ranges of the one or more spectral tiles using parametric spectral envelope information comprised by the encoded audio signal.

6. The apparatus of claim 1,

further comprising a frequency-time converter for converting an envelope-adjusted signal together with the decoded core signal into a time representation.

7. The apparatus in accordance with claim 6, wherein the frequency-time converter is configured for applying an inverse modified discrete cosine transform comprising an overlap/add processing of a current frame with a preceding time frame.

8. The apparatus in accordance with claim 1, wherein the cross-over filter is a controllable filter,

wherein the apparatus further comprises a signal characteristics detector, and wherein the signal characteristics detector is configured for controlling a filter characteristic of the cross-over filter in accordance with a detection result derived from the decoded core signal.

9. The apparatus of claim 8,

wherein the signal characteristics detector is a transient detector, and wherein the transient detector is configured to control the cross-over filter in such a way that, for a more transient signal portion, the cross-over filter has a higher impact on a cross-over filter input signal and that the cross-over filter has a lower impact on the cross-over filter input signal for a less-transient signal portion.

10. The apparatus in accordance with claim 1,

wherein a characteristic of the cross-over filter is defined by a fade-out subfilter characteristic and a fade-in subfilter characteristic,

wherein the fade-in subfilter characteristic h_in(k), and the fade-out subfilter characteristic h_out(k) are defined based on the following equations:

11. The apparatus of claim 10,

wherein Xbias is set between 2 and 20 and wherein N is set between 10 and 50.

12. The apparatus in accordance with claim 1,

wherein the tile generator is configured to generate a preliminary frequency tile, wherein an analyzer is configured for analyzing the preliminary frequency tile, wherein the tile generator is additionally configured for generating a regenerated signal comprising attenuated or eliminated artifact creating tonal portions in relation to the preliminary frequency tile, wherein the file generator is configured to eliminate or attenuate tonal components near frequency tile borders to acquire an input signal into the cross-over filter.

13. The apparatus of claim 12, wherein the tile generator is configured to detect and remove or attenuate tonal spectral portions within a detection range being less than 20% of a bandwidth of a frequency tile or a source range for the regeneration.

14. The apparatus of claim 1, wherein the cross-over filter is configured to cross-over filter within an overlapping range, the overlapping range comprising an upper frequency portion of the decoded core signal and a lower frequency portion of the first frequency tile, or

wherein the cross-over filter is configured to cross-over filter within an overlapping range, the overlapping range comprising an upper frequency portion of a first frequency tile and a lower frequency portion of a second frequency tile.

15. A method of decoding an encoded audio signal comprising an encoded core signal, comprising:

decoding the encoded core signal to acquire a decoded core signal;

generating one or more spectral tiles comprising frequencies not comprised by the decoded core signal using a spectral portion of the decoded core signal; and

spectrally cross-over filtering the decoded core signal and a first frequency tile comprising frequencies extending from a gap filling frequency to an upper border frequency or for spectrally cross-over filtering a first frequency tile and a second frequency tile.

16. A non-transitory digital storage medium having a computer program stored thereon to perform the method of decoding an encoded audio signal comprising an encoded core signal, comprising:

decoding the encoded core signal to acquire a decoded core signal;

generating one or more spectral tiles comprising frequencies not comprised by the decoded core signal using a spectral portion of the decoded core signal; and

spectrally cross-over filtering the decoded core signal and a first frequency tile comprising frequencies extending from a gap filling frequency to an upper border frequency or for spectrally cross-over filtering a first frequency tile and a second frequency tile,

when said computer program is run by a computer.