We are proposing an interpolation technique for head related transfer functions (HRTFs). For deriving the algorithm we study the dual problem where sound is emitted from the listener’s ear and the generated sound field is recorded along a circular array of microphones around the listener. The proposed interpolation algorithm is based on the observation that spatial bandwidth of the measured sound along the circular array is limited (for all practical purposes). Further, we observe that this spatial bandwidth increases linearly with the frequency of the emitted sound. The result of the analysis leads to the conclusion that the necessary angle between HRTFs is about 5 degrees in order to be able to reconstruct all HRTFs up to 44.1 kHz in the horizontal plane.