Method for decoding a higher order ambisonics (HOA) representation of a sound or soundfield
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 and decoding the compressed HOA representation to determine perceptually decoded signals {circumflex over (z)} i (k), i=1, . . . , I, associated gain correction exponent e i (k) and gain correction exception flag β i (k);
providing gain corrected signal frames ŷ i (k), i=1, . . . , I, by performing inverse gain control processing for the perceptually decoded signals {circumflex over (z)} i (k) i=1, . . . , I, the associated gain correction exponent e i (k) and the gain correction exception flag β i (k),
re-distributing the gain corrected signal frames ŷ i (k) i=1, . . . , I, during channel reassignment, in order to reconstruct a frame {circumflex over (X)} PS (k) of predominant sound signals and a frame C I,AMB (k) of an intermediate representation of an ambient HOA component,
wherein a lowest integer number β e of bits applied to a signal of a transport channel in a previous frame is 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.
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 and decoding the compressed HOA representation to determine perceptually decoded signals {circumflex over (z)} i (k), i=1, . . . , I, associated gain correction exponent e i (k) and gain correction exception flag β i (k);
wherein the processor is further configured to provide gain corrected signal frames ŷ i (k), i=1, . . . , I, by performing inverse gain control processing for the perceptually decoded signals {circumflex over (z)} i (k), i=1, . . . , I, the associated gain correction exponent e i (k) and the gain correction exception flag β i (k),
wherein the processor is further configured to re-distribute the gain corrected signal frames ŷ i (k), i=1, . . . , I, during channel reassignment, in order to reconstruct a frame {circumflex over (X)} PS (k) of predominant sound signals and a frame C I,AMB (k) of an intermediate representation of an ambient HOA component,
wherein a lowest integer number β e of bits applied to a signal of a transport channel in a previous frame is 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.