Method for and apparatus for decoding an ambisonics audio soundfield representation for audio playback using 2d setups

Patent metadata

Field	Value
Publication number	US-2016309273-A1
Application number	US-201415030066-A
Country	US
Kind code	A1
Filing date	Oct 20, 2014
Priority date	Oct 23, 2013
Publication date	Oct 20, 2016
Grant date	—

Abstract

Sound scenes in 3D can be synthesized or captured as a natural sound field. For decoding, a decode matrix is required that is specific for a given loudspeaker setup and is generated using the known loudspeaker positions. However, some source directions are attenuated for 2D loudspeaker setups like e.g. 5.1 surround. An improved method for decoding an encoded audio signal in soundfield format for L loudspeakers at known positions comprises steps of adding ( 10 ) a position of at least one virtual loudspeaker to the positions of the L loudspeakers, generating ( 11 ) a 3D decode matrix (D′), wherein the positions (Formula I) of the L loudspeakers and the at least one virtual position (Formula II) are used, downmixing ( 12 ) the 3D decode matrix (D′), and decoding ( 14 ) the encoded audio signal (i 14 ) using the downscaled 3D decode matrix (Formula III). As a result, a plurality of decoded loudspeaker signals (q 14 ) is obtained.

First claim

1 . A method for decoding an encoded audio signal in Ambisonics format for L loudspeakers at known positions, comprising
adding at least one position of at least one virtual loudspeaker to the positions of the L loudspeakers; generating a 3D decode matrix (D′), wherein the positions ({circumflex over (Ω)} 1 , . . . , {circumflex over (Ω)} L ), of the L loudspeakers and the at least one virtual position ({circumflex over (Ω)}′ L+1 ) are used and the 3D decode matrix (D′) has coefficients for said determined and virtual loudspeaker positions; downmixing the 3D decode matrix (D′), wherein the coefficients for the virtual loudspeaker positions are weighted and distributed to coefficients relating to the determined loudspeaker positions, and wherein a downscaled 3D decode matrix ({tilde over (D)}) is obtained having coefficients for the determined loudspeaker positions; and decoding the encoded audio signal using the downscaled 3D decode matrix ({tilde over (D)}), wherein a plurality of decoded loudspeaker signals is obtained.

2 . The method according to claim 1 , wherein the coefficients for the virtual loudspeaker positions are weighted with a weighting factor

g
=

1

L

,

wherein L is the number of loudspeakers.

3 . The method according to claim 1 , wherein the at least one virtual position ({circumflex over (Ω)}′ L+1 ) of a virtual loudspeaker is one of
{circumflex over (Ω)}′ L+1 =[0,0] T and {circumflex over (Ω)}′ L+3 =[π,0] T .

4 . The method according to claim 1 , further comprising a step of normalizing the downscaled 3D decode matrix ({tilde over (D)}) using a Frobenius norm, wherein a normalized downscaled 3D decode matrix (D) is obtained, and the step of decoding the encoded audio signal uses the normalized downscaled 3D decode matrix (D).

5 . The method according to claim 4 , wherein the normalizing is performed according to

D
=

D
~

∑

l
=
1

L



∑

q
=
1

O

3

D

|

d
~

l
,
q



|
2

.

6 . The method according to claim 1 , further comprising
determining positions ({circumflex over (Ω)} 1 . . . {circumflex over (Ω)} L ) of the L loudspeakers and an order N of coefficients of the soundfield signal; determining from the positions that the L loudspeakers are substantially in a 2-dimensional plane; and generating at least one virtual position ({circumflex over (Ω)}′ L+1 ) of a virtual loudspeaker.

7 . The method according to claim 1 , further comprising a step of separating the encoded audio signal into a plurality of frequency bands using band pass filters, wherein a plurality of separate 3D decode matrices (Db′) are generated, one for each frequency band, and each 3D decode matrix (Db′) is downmixed and optionally normalized separately, and wherein the step of decoding the encoded audio signal is performed for each frequency band separately.

8 . The method according to claim 1 , wherein the known L loudspeaker positions are substantially within one 2-dimensional plane, with elevations of not more than 10°.

9 . An apparatus for decoding an encoded audio signal in Ambisonics format for L loudspeakers at known positions, comprising an adder unit adapted for adding at least one position of at least one virtual loudspeaker to the positions of the L loudspeakers;
a decode matrix generator unit adapted for generating a 3D decode matrix (D′), wherein the positions ({circumflex over (Ω)} 1 . . . {circumflex over (Ω)} L ) of the L loudspeakers and the at least one virtual position ({circumflex over (Ω)}′ L+1 ) are used and the 3D decode matrix (D′) has coefficients for said determined and virtual loudspeaker positions; a matrix downmixing unit adapted for downmixing the 3D decode matrix (D′), wherein the coefficients for the virtual loudspeaker positions are weighted and distributed to coefficients relating to the determined loudspeaker positions, and wherein a downscaled 3D decode matrix ({tilde over (D)}) is obtained having coefficients for the determined loudspeaker positions; and a decoding unit for decoding the encoded audio signal using the downscaled 3D decode matrix ({tilde over (D)}), wherein a plurality of decoded loudspeaker signals is obtained.

10 . The apparatus according to claim 9 , further comprising a normalizing unit adapted for normalizing the downscaled 3D decode matrix ({tilde over (D)}) using a Frobenius norm, wherein a normalized downscaled 3D decode matrix (D) is obtained, and the decoding unit uses the normalized downscaled 3D decode matrix (D).

11 . The apparatus according to claim 9 , further comprising
a first determining unit adapted for determining positions ({circumflex over (Ω)} 1 . . . {tilde over (Ω)} L ) of the L loudspeakers and an order N of coefficients of the soundfield signal; a second determining unit adapted for determining from the positions that the L loudspeakers are substantially in a 2-dimensional plane; and a virtual loudspeaker position generating unit adapted for generating at least one virtual position ({circumflex over (Ω)} L+1 ) of a virtual loudspeaker.

12 . The apparatus according to claim 9 , further comprising a plurality of band pass filters adapted for separating the encoded audio signal into a plurality of frequency bands, wherein a plurality of separate 3D decode matrices (D b ′) are generated, one for each frequency band, and each 3D decode matrix (D b ′) is downmixed and optionally normalized separately, and wherein the decoding unit decodes each frequency band separately.

13 . A computer readable storage medium having stored thereon executable instructions to cause a computer to perform a method for decoding an encoded audio signal in Ambisonics format for L loudspeakers at known positions, the method comprising
adding at least one position of at least one virtual loudspeaker to the positions of the L loudspeakers; gen

Assignees

• Thomson Licensing

Inventors

• Keiler Florian
• HOEHM Johannes

Classifications

• H04S3/02 Primary

  of the matrix type, i.e. in which input signals are combined algebraically, e.g. after having been phase shifted with respect to each other · CPC title

• H04S2420/11

  Application of ambisonics in stereophonic audio systems · CPC title

• H04S2420/07

  Synergistic effects of band splitting and sub-band processing · CPC title

• H04S2400/11

  Positioning of individual sound objects, e.g. moving airplane, within a sound field (H04S2420/13 takes precedence) · CPC title

• H04S7/308

  Electronic adaptation dependent on speaker or headphone connection · CPC title