A gain phase equalization, GPEQ, filter for pre-conditioning at least two transaural audio signals carried in respective audio channels for transaural reproduction at a listener position by an audio device having a like number of audio speakers that exhibit an asymmetric magnitude response, said GPEQ filter comprising: an asymmetric FIR filter bank configured to normalize the magnitude responses of the at least two audio speakers to a target response above a low frequency cross-over Fc of the audio speakers as reproduced at the listener position; characterised in that the GPEQ filter further comprises: an IIR filter bank including a symmetric IIR filter bank component configured to high pass filter above the low frequency cross-over Fc and equalize the normalized magnitude responses of the at least two audio speakers as reproduced at the listener position while maintaining a relative phase relationship of the transaural audio signals, wherein the IIR filter bank further includes an asymmetric IIR filter bank component configured to correct residual asymmetry in the normalized magnitude responses of the at least two audio speakers as reproduced at the listener position near the low-frequency cross-over Fc while preserving the relative phases of the at least two transaural audio signals, and wherein the symmetric IIR filter bank component and the asymmetric IIR filter bank component are configured to operate in sequential order. an asymmetric FIR filter bank configured to normalize the magnitude responses of the at least two audio speakers to a target response above a low frequency cross-over Fc of the audio speakers as reproduced at the listener position; characterised in that the GPEQ filter further comprises: an IIR filter bank including a symmetric IIR filter bank component configured to high pass filter above the low frequency cross-over Fc and equalize the normalized magnitude responses of the at least two audio speakers as reproduced at the listener position while maintaining a relative phase relationship of the transaural audio signals, wherein the IIR filter bank further includes an asymmetric IIR filter bank component configured to correct residual asymmetry in the normalized magnitude responses of the at least two audio speakers as reproduced at the listener position near the low-frequency cross-over Fc while preserving the relative phases of the at least two transaural audio signals, and wherein the symmetric IIR filter bank component and the asymmetric IIR filter bank component are configured to operate in sequential order. an IIR filter bank including a symmetric IIR filter bank component configured to high pass filter above the low frequency cross-over Fc and equalize the normalized magnitude responses of the at least two audio speakers as reproduced at the listener position while maintaining a relative phase relationship of the transaural audio signals, wherein the IIR filter bank further includes an asymmetric IIR filter bank component configured to correct residual asymmetry in the normalized magnitude responses of the at least two audio speakers as reproduced at the listener position near the low-frequency cross-over Fc while preserving the relative phases of the at least two transaural audio signals, and wherein the symmetric IIR filter bank component and the asymmetric IIR filter bank component are configured to operate in sequential order. <EOS>