Method for decoding a mixed spatial/coefficient domain representation (d,w;D,W) of coded HOA signals, wherein the number of said HOA signals can be variable over time in successive coefficient frames, said decoding including: - receiving multiplexed vectors of PCM encoded spatial domain signals ( w' 1, W' 1) and PCM encoded and normalised coefficient domain signals ( d" 2, D" 2); - receiving side information; - de-multiplexing (24, 34) said multiplexed vectors of PCM encoded spatial domain signals ( w' 1, W' 1) and PCM encoded and normalised coefficient domain signals ( d" 2, D" 2); - transforming (25, 35) said vector ( w' 1, W' 1) of PCM encoded spatial domain signals to a corresponding vector ( d' 1, D' 1) of coefficient domain signals by multiplying said vector of PCM encoded spatial domain signals with a transform matrix (Ψ); characterized in that - de-normalising (28, 38) said vector ( d" 2, D" 2)of PCM encoded and normalised coefficient domain signals, wherein said de-normalising includes: -- computing, using a corresponding exponent e n ( j - 1) of the received side information ( e) and a recursively computed gain value g n ( j - 2), a transition vector h n ( j - 1), wherein a gain value g n ( j - 1) for the corresponding processing of a following vector ( D" 2) of the PCM encoded and normalised coefficient domain signals to be processed is kept, j being a running index of an input matrix of HOA signal vectors; -- applying the transition vector to a current vector x n " j − 1, D " 2 of the PCM-coded and normalised signal so as to get a corresponding vector x n ′′′ j − 1, D ′′′ 2 of the PCM-coded and de-normalised signal; - combining (29, 39) said vector ( d' 1, D' 1) of coefficient domain signals and the vector ( d′′′ 2, D′′′ 2) of de-normalised coefficient domain signals so as to get a combined vector ( d',D') of HOA coefficient domain signals that can have a variable number of HOA coefficients. - receiving multiplexed vectors of PCM encoded spatial domain signals ( w' 1, W' 1) and PCM encoded and normalised coefficient domain signals ( d" 2, D" 2); - receiving side information; - de-multiplexing (24, 34) said multiplexed vectors of PCM encoded spatial domain signals ( w' 1, W' 1) and PCM encoded and normalised coefficient domain signals ( d" 2, D" 2); - transforming (25, 35) said vector ( w' 1, W' 1) of PCM encoded spatial domain signals to a corresponding vector ( d' 1, D' 1) of coefficient domain signals by multiplying said vector of PCM encoded spatial domain signals with a transform matrix (Ψ); - de-normalising (28, 38) said vector ( d" 2, D" 2)of PCM encoded and normalised coefficient domain signals, wherein said de-normalising includes: -- computing, using a corresponding exponent e n ( j - 1) of the received side information ( e) and a recursively computed gain value g n ( j - 2), a transition vector h n ( j - 1), wherein a gain value g n ( j - 1) for the corresponding processing of a following vector ( D" 2) of the PCM encoded and normalised coefficient domain signals to be processed is kept, j being a running index of an input matrix of HOA signal vectors; -- applying the transition vector to a current vector x n " j − 1, D " 2 of the PCM-coded and normalised signal so as to get a corresponding vector x n ′′′ j − 1, D ′′′ 2 of the PCM-coded and de-normalised signal; -- computing, using a corresponding exponent e n ( j - 1) of the received side information ( e) and a recursively computed gain value g n ( j - 2), a transition vector h n ( j - 1), wherein a gain value g n ( j - 1) for the corresponding processing of a following vector ( D" 2) of the PCM encoded and normalised coefficient domain signals to be processed is kept, j being a running index of an input matrix of HOA signal vectors; -- applying the transition vector to a current vector x n " j − 1, D " 2 of the PCM-coded and normalised signal so as to get a corresponding vector x n ′′′ j − 1, D ′′′ 2 of the PCM-coded and de-normalised signal; - combining (29, 39) said vector ( d' 1, D' 1) of coefficient domain signals and the vector ( d′′′ 2, D′′′ 2) of de-normalised coefficient domain signals so as to get a combined vector ( d',D') of HOA coefficient domain signals that can have a variable number of HOA coefficients.