Allpass decorrelating filter design and evaluation

By breaking up the phase coherence of a signal broadcast from multiple loudspeakers, it is possible to control the perceived spatial extent and location of a sound source. This so-called signal decorrelation process is commonly achieved using a set of linear filters, and finds applications in audio upmixing, spatialization, and auralization. It is important that any individual decorrelating filter does not perceivably alter the sound of its input, i.e., that it does not color the signal spectrum or smear transients over time. In that way, the process will only affect the spatial properties of the sound. Allpass filters make ideal decorrelation filters since they have unit magnitude spectra, and therefore can be perceptually transparent. By manipulating their phase, allpass filters can be leveraged to achieve a degree of decorrelation. Here, we present a method for designing allpass decorrelation filters by specifying group delay trajectories in a way that allows for control of the amount of correlation as...