Method for compressing a higher order ambisonics (HOA) signal, method for decompressing a compressed HOA signal, apparatus for compressing a HOA signal, and apparatus for decompressing a compressed HOA signal
A method for compressing a HOA signal being an input HOA representation with input time frames (C(k)) of HOA coefficient sequences comprises spatial HOA encoding of the input time frames and subsequent perceptual encoding and source encoding. Each input time frame is decomposed ( 802 ) into a frame of predominant sound signals (X PS (k−1)) and a frame of an ambient HOA component (C AMB (k−1)). The ambient HOA component (C ˜ AMB (k−1)) comprises, in a layered mode, first HOA coefficient sequences of the input HOA representation (c n (k−1)) in lower positions and second HOA coefficient sequences (c AMB,n (k−1)) in remaining higher positions. The second HOA coefficient sequences are part of an HOA representation of a residual between the input HOA representation and the HOA representation of the predominant sound signals.
1. A method of decoding a compressed Higher Order Ambisonics (HOA) representation of a sound or soundfield, the method comprising:
receiving a bit stream containing the compressed HOA representation;
decoding, based on a determination that there are multiple layers, the compressed HOA representation from the bitstream to obtain a sequence of decoded HOA representations,
wherein a first subset of the sequence of decoded HOA representations is determined based only on corresponding ambient HOA components, and
wherein a second subset of the sequence of decoded HOA representations is determined based on corresponding ambient HOA components and corresponding predominant sound components,
wherein, for a frame k, the sequence of decoded HOA representations are represented at least in part by
c
^
~
n
(
k
-
1
)
=
{
c
^
~
AMB
,
n
(
k
-
1
)
for
n
in
the
first
subset
c
^
n
(
k
-
1
)
=
c
^
PS
,
n
(
k
-
1
)
+
c
^
AMB
,
n
(
k
-
1
)
,
for
n
in
the
second
subset
wherein ĉ AMB,n (k−1) corresponds to the corresponding ambient HOA components and ĉ PS,n (k−1) corresponds to the corresponding predominant sound components,
wherein an indication of the multiple layers is signaled in the bitstream, and wherein the multiple layers include a base layer and at least an enhancement layer that are independently decodable of one another.
2. The method of claim 1 , further determining, based on a determination that there are not multiple layers, that there is a single layer, and, based on the determination of the single layer, determining, for a frame k, a single layer decoded HOA representation based on an addition of a corresponding predominant HOA sound component (Ĉ PS (k−1)) and a corresponding ambient HOA component ({tilde over (Ĉ)} AMB (k−1)).
3. An apparatus for decoding a compressed Higher Order Ambisonics (HOA) representation of a sound or a soundfield, the apparatus comprising:
a receiver for receiving a bit stream containing the compressed HOA representation;
an audio decoder for decoding, based on a determination that there are multiple layers, the compressed HOA representation from the bitstream to obtain a sequence of decoded HOA representations,
wherein a first subset of the sequence of decoded HOA representations is determined based only on corresponding ambient HOA components, and
wherein a second subset of the sequence of decoded HOA representations is determined based on corresponding ambient HOA components and corresponding predominant sound components,
wherein, for a frame k, the sequence of decoded HOA representations are represented at least in part by
c
^
~
n
(
k
-
1
)
=
{
c
^
AMB
,
n
(
k
-
1
)
for
n
in
the
first
subset
c
^
n
(
k
-
1
)
=
c
^
PS
,
n
(
k
-
1
)
+
c
^
AMB
,
n
(
k
-
1
)
,
for
n
in
the
second
subset
wherein ĉ AMB,n (k−1) corresponds to the corresponding ambient HOA components and ĉ PS,n (k−1) corresponds to the corresponding predominant sound components, wherein an indication of the multiple layers is signaled in the bitstream, and wherein the multiple layers include a base layer and at least an enhancement layer that are independently decodable of one another.
4. The apparatus of claim 3 , wherein the audio decoder is further configured to determine, based on a determination that there are not multiple layers, that there is a single layer, and, based on the determination of the single layer, determining a single layer decoded HOA representation based on an addition of a corresponding predominant HOA sound component (Ĉ PS (k−1)) and a corresponding ambient HOA component ({tilde over (Ĉ)} AMB (k−1)).
5. A non-transitory computer readable storage medium containing instructions that when executed by a processor perform a method of decoding a compressed Higher Order Ambisonics (HOA) representation of a sound or soundfield, comprising:
receiving a bit stream containing the compressed HOA representation;
decoding, based on a determination that there are multiple layers, the compressed HOA representation from the bitstream to obtain a sequence of decoded HOA representations,
wherein a first subset of the sequence of decoded HOA representations is determined based only on corresponding ambient HOA components, and
wherein a second subset of the sequence of decoded HOA representations is determined based on corresponding ambient HOA components and corresponding predominant sound components,
wherein, for a frame k, the sequence of decoded HOA representations are represented at least in part by
c
^
~
n
(
k
-
1
)
=
{
c
^
~
AMB
,
n
(
k
-
1
)
for
n
in
the
first
subset
c
^
n
(
k
-
1
)
=
c
^
PS
,
n
(
k
-
1
)
+
c
^
AMB
,
n
(
k
-
1
)
,
for
n
in
the
second
subset
wherein ĉ AMB,n (k−1) corresponds to the corresponding ambient HOA components and ĉ PS,n (k−1) corresponds to the corresponding predominant sound components, wherein an indication of the multiple layers is signaled in the bitstream, and wherein the multiple layers include a base layer and at least an enhancement layer that are independently decodable of one another.