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

Patent metadata

Field	Value
Publication number	US-10515652-B2
Application number	US-201815985930-A
Country	US
Kind code	B2
Filing date	May 22, 2018
Priority date	Jul 22, 2013
Publication date	Dec 24, 2019
Grant date	Dec 24, 2019

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.

First claim

The invention claimed is:

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:

h
out

⁡

(
k
)

=

h
in

⁡

(

N
-
1
-
k

)

,

∀
Xbias

h
out

⁡

(
k
)

+

h
in

⁡

(
k
)

=
1

,

Xbias
=
0

h
out

⁡

(
k
)

=

0.5
+

0.5
·

cos
⁡

(

k

N
-
1
-
Xbias

·
π

Assignees

• Fraunhofer Ges Forschung

Inventors

• Disch Sascha
• Geiger Ralf
• Helmrich Christian
• Nagel Frederik
• Neukam Christian
• Schmidt Konstantin
• Fischer Michael

Classifications

• G10L21/038

  using band spreading techniques · CPC title

• G10L19/02 Primary

  using spectral analysis, e.g. transform vocoders or subband vocoders · CPC title

• G10L19/032

  Quantisation or dequantisation of spectral components · CPC title

• G10L19/0212

  using orthogonal transformation · CPC title

• G10L19/008 Primary

  Multichannel audio signal coding or decoding using interchannel correlation to reduce redundancy, e.g. joint-stereo, intensity-coding or matrixing · CPC title