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

An apparatus for determining for the compression of an HOA data frame representation (C(k)) a lowest integer number βe of bits for describing representations of non-differential gain values corresponding to amplitude changes as an exponent of two (2e) for channel signals of the HOA data frames,

• wherein each channel signal in each frame comprises a group of sample values and wherein to each channel signal (y1(k−2), . . . , yI(k−2)) of each one of the HOA data frames a differential gain value is assigned, wherein the differential gain value causes a change of amplitudes of first sample values of a channel signal in a current HOA data frame ((k−2)) with respect to second sample values of a channel signal in a previous HOA data frame ((k−3)), and wherein resulting gain adapted channel signals are encoded in an encoder,
• and wherein the HOA data frame representation (C(k)) was rendered in a spatial domain to 0 virtual loudspeaker signals wj(t), wherein positions of the virtual loudspeakers are lying on a unit sphere and are targeted to be distributed uniformly on that unit sphere, said rendering being represented by a matrix multiplication w(t)=(Ψ)−1·c(t), wherein w(t) is a vector containing all virtual loudspeaker signals, Ψ is a virtual loudspeaker positions mode matrix, and c(t) is a vector of the corresponding HOA coefficient sequences of the HOA data frame representation,
• and wherein said HOA data frame representation (C(k)) was normalised such that
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• said apparatus including:
• a processor configured to form said channel signals (y1(k−2), . . . , yI(k−2)) by:
• a) for representing predominant sound signals (x(t)) in said channel signals, multiplying said vector of HOA coefficient sequences c(t) by a mixing matrix A, the Euclidean norm of which mixing matrix A is not greater than ‘1’, wherein mixing matrix A represents a linear combination of coefficient sequences of a normalised HOA data frame representation;
• b) for representing an ambient component cAMB(t) in the channel signals, subtracting the predominant sound signals from the normalised HOA data frame representation, and selecting at least part of the coefficient sequences of said ambient component cAMB(t), wherein ∥cAMB(t)∥22≦∥c(t)∥22, and transforming a resulting minimum ambient component cAMB,MIN(t) by computing wMIN(t)=ΨMIN−1·cAMB,MIN(t), wherein ∥ΨMIN−1∥2<1 and ΨMIN is a mode matrix for said minimum ambient component CAMB,MIN(t);
• c) selecting part of the HOA coefficient sequences c(t) that relate to coefficient sequences of the ambient HOA component to which a spatial transform is applied, and the minimum order NMIN describing the number of said selected coefficient sequences is NMIN≦9;
• a processor configured to determine the integer number βe of bits based on βe=┌log2(┌log2(√{square root over (KMAX)}·0)┐+1)┐,
• wherein KMAX=max1≦N≦NMAX K(N, Ω1(N), . . . , Ω0(N)), N is the order, NMAX is a maximum order of interest, Ω1(N), . . . , Ω0(N) are directions of said virtual loudspeakers, 0=(N+1)2 is the number of HOA coefficient sequences, and K is a ratio between the squared Euclidean norm ∥Ψ∥22 of said mode matrix and 0.

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 ei(k) and gain correction exception flag βi(k);
• providing gain corrected signal frames ŷi(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 ei(k) and the gain correction exception flag βi(k),
• re-distributing the gain corrected signal frames ŷi(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 CI,AMB(k) of an intermediate representation of an ambient HOA component,
• wherein a lowest integer number βe of bits applied to a signal of a transport channel in a previous frame is based on
• βe=┌log2(┌log2(√{square root over (KMAX)}·0)┐+1)┐,
• wherein KMAX=max1≦N≦NMAXK(N, Ω1(N), . . . , Ω0(N)), N is the order, NMAX is a maximum order of interest, Ω1(N), . . . , Ω0(N) are directions of said virtual loudspeakers, 0=(N+1)2 is the number of HOA coefficient sequences, and K is a ratio between the squared Euclidean norm ∥Ψ∥22 of said mode matrix and 0.

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 ei(k) and gain correction exception flag βi(k);
• wherein the processor is further configured to provide gain corrected signal frames ŷi(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 ei(k) and the gain correction exception flag βi(k),
• wherein the processor is further configured to re-distribute the gain corrected signal frames ŷi(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 CI,AMB(k) of an intermediate representation of an ambient HOA component,
• wherein a lowest integer number βe of bits applied to a signal of a transport channel in a previous frame is based on
• βe=┌log2(┌log2(√{square root over (KMAX)}·0)┐+1)┐,
• wherein KMAX=max1≦N≦NMAX K(N, Ω1(N), . . . , Ω0(N)), N is the order, NMAX is a maximum order of interest, Ω1(N), . . . , Ω0(N) are directions of said virtual loudspeakers, 0=(N+1)2 is the number of HOA coefficient sequences, and K is a ratio between the squared Euclidean norm ∥Ψ∥22 of said mode matrix and 0.