A method for synthesizing sound, comprising: receiving first inputs comprising a first plurality of monaural audio tracks, such that each first input comprises a respective monaural audio track; receiving second inputs indicating respective three-dimensional source locations having azimuth and elevation coordinates to be associated with the first inputs; assigning to each of the first inputs respective left and right filter responses based on filter response functions that depend upon the azimuth and elevation coordinates of the respective 3D source locations; and synthesizing left and right stereo output signals by applying the respective left and right filter responses to the first inputs, wherein synthesizing the left and right stereo output signals comprises: spatially upsampling the first plurality of the monaural audio tracks in order to generate a second plurality of synthesized inputs, having synthesized 3D source locations with respective coordinates different from the respective 3D source locations associated with the first inputs; filtering the synthesized inputs using the filter response functions computed at the azimuth and elevation coordinates of the synthesized 3D source locations; and after filtering the first inputs using the respective left and right filter responses, summing the filtered synthesized inputs with the filtered first inputs to produce the stereo output signals, characterized in that spatially upsampling the first plurality of the monaural audio tracks comprises applying a wavelet transform to the monaural audio tracks to generate respective spectrograms of the monaural audio tracks, and interpolating between the spectrograms according to the 3D source locations to generate the synthesized inputs. receiving first inputs comprising a first plurality of monaural audio tracks, such that each first input comprises a respective monaural audio track; receiving second inputs indicating respective three-dimensional source locations having azimuth and elevation coordinates to be associated with the first inputs; assigning to each of the first inputs respective left and right filter responses based on filter response functions that depend upon the azimuth and elevation coordinates of the respective 3D source locations; and synthesizing left and right stereo output signals by applying the respective left and right filter responses to the first inputs, wherein synthesizing the left and right stereo output signals comprises: spatially upsampling the first plurality of the monaural audio tracks in order to generate a second plurality of synthesized inputs, having synthesized 3D source locations with respective coordinates different from the respective 3D source locations associated with the first inputs; filtering the synthesized inputs using the filter response functions computed at the azimuth and elevation coordinates of the synthesized 3D source locations; and after filtering the first inputs using the respective left and right filter responses, summing the filtered synthesized inputs with the filtered first inputs to produce the stereo output signals, characterized in that spatially upsampling the first plurality of the monaural audio tracks comprises applying a wavelet transform to the monaural audio tracks to generate respective spectrograms of the monaural audio tracks, and interpolating between the spectrograms according to the 3D source locations to generate the synthesized inputs. spatially upsampling the first plurality of the monaural audio tracks in order to generate a second plurality of synthesized inputs, having synthesized 3D source locations with respective coordinates different from the respective 3D source locations associated with the first inputs; filtering the synthesized inputs using the filter response functions computed at the azimuth and elevation coordinates of the synthesized 3D source locations; and after filtering the first inputs using the respective left and right filter responses, summing the filtered synthesized inputs with the filtered first inputs to produce the stereo output signals, characterized in that spatially upsampling the first plurality of the monaural audio tracks comprises applying a wavelet transform to the monaural audio tracks to generate respective spectrograms of the monaural audio tracks, and interpolating between the spectrograms according to the 3D source locations to generate the synthesized inputs.