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-2016140979-A1
Application number	US-201615002343-A
Country	US
Kind code	A1
Filing date	Jan 20, 2016
Priority date	Jul 22, 2013
Publication date	May 19, 2016
Grant date	—

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

1 . 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, 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 subfilter 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.

2 . 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.

3 . Apparatus of claim 1 ,
wherein the cross-over filter is configured for applying a cosine-like filter characteristic for fading-in and fading-out.

4 . 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.

5 . 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.

6 . Apparatus in accordance with claim 5 , 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.

7 . 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.

8 . Apparatus of claim 7 ,
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 first impact on a cross-over filter input signal and that the cross-over filter has a second impact on the cross-over filter input signal for a less-transient signal portion, wherein the first impact is higher than the second impact.

9 . 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
-
l

)

,



∀
Xbias

h
out



(
k
)

+

h
in



(
k
)

=
1

,



Xbias
=
0

h
out



(
k
)

=

0.5
+

0.5
·

cos


(

k

N
-
1
-
Xbias

·
π

)

,



k
=
0

,
1
,
…


,

N
-
1
-
Xbias

wherein Xbias is an integer defining a slope of both filters extending between zero and an integer N, wherein k is a frequency index extending between zero and N−1, and wherein N is an additional integer, and wherein different values for N and Xbias result in different cross-over filter characteristics.

10 . Apparatus of claim 9 ,
wherein Xbias is se

Assignees

• Fraunhofer Ges Forschung

Inventors

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

Classifications

• G10L19/0204

  using subband decomposition · CPC title

• G10L21/0388 Primary

  Details of processing therefor · CPC title

• G10L19/032

  Quantisation or dequantisation of spectral components · CPC title

• G10L19/028

  Noise substitution, i.e. substituting non-tonal spectral components by noisy source (comfort noise for discontinuous speech transmission G10L19/012) · CPC title

• H03M7/30

  Compression (speech analysis-synthesis for redundancy reduction G10L19/00; for image communication H04N); Expansion; Suppression of unnecessary data, e.g. redundancy reduction · CPC title