Abstract: This sound processing system creates surround effects by minimizing quality degradation experienced by known sound processing systems in non-optimum listening environments such as vehicles. The sound processing system may include taking two channel input stereo signals and upmixing the input signals into at least two output signals where the phase of the output signals remains unchanged from the input signals. Once the output signals are generated by the upmixer, all pass filters can be adjusted based on the distance of the listeners from the loudspeakers to obtain the desired all pass filter frequencies and Q values.