Method and apparatus for determining for the compression of an HOA data frame representation a lowest integer number of bits required for representing non-differential gain values
When compressing an HOA data frame representation, a gain control ( 15, 151 ) is applied for each channel signal before it is perceptually encoded ( 16 ). The gain values are transferred in a differential manner as side information. However, for starting decoding of such streamed compressed HOA data frame representation absolute gain values are required, which should be coded with a minimum number of bits. For determining such lowest integer number (β e ) of bits the HOA data frame representation (C(k)) is rendered in spatial domain to virtual loudspeaker signals lying on a unit sphere, followed by normalisation of the HOA data frame representation (C(k)). Then the lowest integer number of bits is set to β e =┌log 2 (┌log 2 (√{square root over (K MAX )}·O)┐+1)┐.
1. A method of decoding a compressed Higher Order Ambisonics (HOA) sound representation of a sound or sound field, the method comprising:
receiving a bit stream containing the compressed HOA representation, wherein the bitstream includes a number of HOA coefficients corresponding to the compressed HOA representation, and
decoding the compressed HOA representation based on a lowest integer number β e , wherein the lowest integer number β e is determined based on β e =┌log 2 (┌log 2 (√{square root over (K MAX )}·O)┐+1)┐,
wherein
K MAX =max 1≤N≤N MAX K ( N,Ω 1 (N) , . . . ,Ω O (N) ),
N is the order, N MAX is a maximum order of interest, Ω 1 (N) , . . . , Ω O (N) are directions of said virtual loudspeakers, O=(N+1) is the number of HOA coefficient sequences, and K is a ratio between the squared Euclidean norm ∥Ψ∥ 2 2 of said mode matrix and O,
wherein √{square root over (K MAX )}=1.5.
2. An apparatus for decoding a compressed Higher Order Ambisonics (HOA) sound representation of a sound or sound field, the apparatus comprising:
a processor configured to receive a bit stream containing the compressed HOA representation, wherein the bitstream includes a number of HOA coefficients corresponding to the compressed HOA representation, and the processor further configured to decode the compressed HOA representation based on a lowest integer number β e , wherein the lowest integer number β e is determined based on β e =┌log 2 (┌log 2 (√{square root over (K MAX )}·O)┐+1)┐,
wherein
K MAX =max 1≤N≤N MAX K ( N,Ω 1 (N) , . . . , Ω O (N) ),
N is the order, N MAX is a maximum order of interest, Ω 1 (N) , . . . , Ω O (N) are directions of said virtual loudspeakers, O=(N+1) 2 is the number of HOA coefficient sequences, and K is a ratio between the squared Euclidean norm ∥Ψ∥ 2 2 of said mode matrix and O,
wherein √{square root over (K MAX )}=1.5.
3. A non-transitory computer readable storage medium containing instructions that when executed by a processor perform a method according to claim 1 .