Decoder for decoding an encoded audio signal and encoder for encoding an audio signal

Patent metadata

Field	Value
Publication number	US-10236008-B2
Application number	US-201715696934-A
Country	US
Kind code	B2
Filing date	Sep 6, 2017
Priority date	Mar 9, 2015
Publication date	Mar 19, 2019
Grant date	Mar 19, 2019

Abstract

A schematic block diagram of a decoder for decoding an encoded audio signal is shown. The decoder includes an adaptive spectrum-time converter and an overlap-add-processor. The adaptive spectrum-time converter converts successive blocks of spectral values into successive blocks of time values, e.g. via a frequency-to-time transform. Furthermore, the adaptive spectrum-time converter receives a control information and switches, in response to the control information, between transform kernels of a first group of transform kernels including one or more transform kernels having different symmetries at sides of a kernel, and a second group of transform kernels including one or more transform kernels having the same symmetries at sides of a transform kernel. Moreover, the overlap-add-processor overlaps and adds the successive blocks of time values to obtain decoded audio values, which may be a decoded audio signal.

First claim

The invention claimed is:

1. Audio decoder for decoding an encoded audio signal, the audio decoder comprising:
an adaptive spectrum-time converter for converting successive blocks of spectral values into successive blocks of time values; and
an overlap-add-processor for overlapping and adding successive blocks of time values to acquire decoded audio values,
wherein the adaptive spectrum-time converter is configured to receive a control information and to switch, in response to the control information, between transform kernels of a first group of transform kernels comprising one or more transform kernels comprising different symmetries at sides of a kernel, and a second group of transform kernels comprising one or more transform kernels comprising the same symmetries at sides of a transform kernel, and
wherein one or more of the adaptive spectrum-time converter, and the overlap-add-processor is implemented, at least in part, by one or more hardware elements of the audio decoder.

2. Audio decoder of claim 1 ,
wherein the first group of transform kernels comprises one or more transform kernels comprising an odd symmetry at a left side and an even symmetry at the right side of the kernel or vice versa, and wherein the second group of transform kernels comprises one or more transform kernels comprising an even symmetry at both sides or an odd symmetry at both sides of the kernel.

3. Audio decoder of claim 1 ,
wherein the first group of transform kernels comprises an inverse MDCT-IV transform kernel or an inverse MDST-IV transform kernel, and wherein the second group of transform kernels comprises an inverse MDCT-II transform kernel or an inverse MDST-II transform kernel.

4. Audio decoder of claim 1 ,
wherein the transform kernel of the first group and the second group is based on the following equation:

x

i
,
n

=

C
⁢

∑

k
=
0

M
-
1

⁢

spec
⁡

[
i
]

⁡

[
k
]

⁢

⁢

cs
⁡

(

2
⁢

⁢
π

N

⁢

(

n
+

n
0

)

⁢

(

k
+

k
0

)

)

wherein the at least one transform kernel of the first group is based on the parameters:
cs ( )=cos( ) and k 0 =0.5 or
cs ( )=sin( ) and k 0 =0.5, or

wherein the at least one transform kernel of the second group is based on the parameters:
cs ( )=cos( ) and k 0 =0; or
cs ( )=sin( ) and k 0 =1,

wherein x i,n is a time domain output, C is a constant parameter, N is a time-window length, spec are spectral values comprising M values for a block, M is equal to N/2, i is a time block index, k is a spectral index indicating a spectral values, n is a time index indicating a time value in a block i, and n o is a constant parameter being an integer number or zero.

5. Audio decoder of claim 1 , wherein the control information comprises a current bit indicating a current symmetry for a current frame, and
wherein the adaptive spectrum-time converter is configured to not switch from the first group to the second group, when the current bit indicates the same symmetry as was used in a preceding frame, and
wherein the adaptive spectrum-time converter is configured to switch from the first group to the second group, when the current bit indicates a different symmetry as was used in the preceding frame.

6. Audio decoder of claim 1 ,
wherein the adaptive spectrum-time converter is configured to switch the second group into the first group, when a current bit indicating a current symmetry for a current frame indicates the same symmetry as was used in the preceding frame, and
wherein the adaptive spectrum-time converter is configured to not switch from the second group into the first group, when the current bit indicates a current symmetry for the current frame comprising a different symmetry as was used in the preceding frame.

7. Audio decoder of claim 1 ,
wherein the adaptive spectrum-time converter is configured to read from the encoded audio signal the control information for a previous frame and a control information for a current frame following the previous frame from the encoded audio signal in a control data section for the current frame, or
wherein the adaptive spectrum-time converter is configured to read the control information from the control data section for the current frame and to retrieve the control information for the previous frame from a control data section of the previous frame or from an audio decoder setting applied to the previous frame.

8. Audio decoder of claim 1 ,
wherein the adaptive spectrum-time converter is configured to apply the transform kernel based on the following table:

current frame i

right-side symmetry
right-side symmetry

last frame i − 1
even (symm i = 0)
odd (symm i = 1)

Assignees

• Fraunhofer Ges Forschung

Inventors

• Helmrich Christian
• Edler Bernd

Classifications

• G10L19/18 Primary

  Vocoders using multiple modes · CPC title

• G10L19/0212 Primary

  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

• G10L19/032

  Quantisation or dequantisation of spectral components · CPC title

• G10L19/02

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