A method for reconstructing an N -channel audio signal, wherein N ≥ 3, the method comprising: receiving a single-channel downmix signal together with associated dry and wet upmix parameters ( C̃,P̃); computing a dry upmix signal as a linear mapping of the downmix signal, wherein a set of dry upmix coefficients is applied to the downmix signal; generating a decorrelated signal based on the downmix signal, wherein the decorrelated signal has N - 1 channels; computing a wet upmix signal as a linear mapping of the N - 1 channels of the decorrelated signal, wherein a set of wet upmix coefficients is applied to the N - 1 channels of the decorrelated signal; and combining the dry and wet upmix signals to obtain a multidimensional reconstructed signal ( X̂) corresponding to the N -channel audio signal to be reconstructed, wherein the method further comprises: determining the set of dry upmix coefficients based on the received dry upmix parameters; populating an intermediate matrix having more elements than the number of received wet upmix parameters, based on the received wet upmix parameters and knowing that the intermediate matrix belongs to a predefined matrix class, wherein known properties of all matrices in the predefined matrix class include known relations between predefined matrix elements or predefined matrix elements being zero; and obtaining the set of wet upmix coefficients by multiplying the intermediate matrix by a predefined matrix, wherein the set of wet upmix coefficients corresponds to the matrix resulting from the multiplication and includes more coefficients than the number of elements in the intermediate matrix. receiving a single-channel downmix signal together with associated dry and wet upmix parameters ( C̃,P̃); computing a dry upmix signal as a linear mapping of the downmix signal, wherein a set of dry upmix coefficients is applied to the downmix signal; generating a decorrelated signal based on the downmix signal, wherein the decorrelated signal has N - 1 channels; computing a wet upmix signal as a linear mapping of the N - 1 channels of the decorrelated signal, wherein a set of wet upmix coefficients is applied to the N - 1 channels of the decorrelated signal; and combining the dry and wet upmix signals to obtain a multidimensional reconstructed signal ( X̂) corresponding to the N -channel audio signal to be reconstructed, wherein the method further comprises: determining the set of dry upmix coefficients based on the received dry upmix parameters; populating an intermediate matrix having more elements than the number of received wet upmix parameters, based on the received wet upmix parameters and knowing that the intermediate matrix belongs to a predefined matrix class, wherein known properties of all matrices in the predefined matrix class include known relations between predefined matrix elements or predefined matrix elements being zero; and obtaining the set of wet upmix coefficients by multiplying the intermediate matrix by a predefined matrix, wherein the set of wet upmix coefficients corresponds to the matrix resulting from the multiplication and includes more coefficients than the number of elements in the intermediate matrix. determining the set of dry upmix coefficients based on the received dry upmix parameters; populating an intermediate matrix having more elements than the number of received wet upmix parameters, based on the received wet upmix parameters and knowing that the intermediate matrix belongs to a predefined matrix class, wherein known properties of all matrices in the predefined matrix class include known relations between predefined matrix elements or predefined matrix elements being zero; and obtaining the set of wet upmix coefficients by multiplying the intermediate matrix by a predefined matrix, wherein the set of wet upmix coefficients corresponds to the matrix resulting from the multiplication and includes more coefficients than the number of elements in the intermediate matrix.