A signal processing device comprising: a calculating unit which is configured to perform calculation using a signal level of a first acoustic signal Lin and a signal level of a second acoustic signal Rin, wherein the signals Lin and Rin are two-channel stereo music input signals; a determining unit configured to determine whether a component of a third acoustic signal to be output from a position between a position from which the first acoustic signal Lin is to be output and a position from which the second acoustic signal Rin is to be output is included in the first acoustic signal Lin and the second acoustic signal Rin, based on a result of a comparison between: - the signal level of at least one of the first acoustic signal Lin and the second acoustic signal Rin before the calculation; - and a result of the calculation; the signal processing device further comprising: a signal generating unit which is configured to generate the third acoustic signal from the first acoustic signal Lin and the second acoustic signal Rin when the determining unit determines that the component of the third acoustic signal is included in the first acoustic signal Lin and the second acoustic signal Rin; wherein the determining unit is configured to determine that the component of the third acoustic signal is included in the first acoustic signal Lin and the second acoustic signal Rin when at least one condition of four conditions represented by (Lin + Rin) > Lin, (Lin + Rin) > Rin, (Lin - Rin) < Lin and (Lin - Rin) < Rin are satisfied; wherein the values of Lin, Rin, (Lin + Rin), (Lin - Rin) are absolute values, and Lin, Rin being amplitude values of the first and the second acoustic signals. a calculating unit which is configured to perform calculation using a signal level of a first acoustic signal Lin and a signal level of a second acoustic signal Rin, wherein the signals Lin and Rin are two-channel stereo music input signals; a determining unit configured to determine whether a component of a third acoustic signal to be output from a position between a position from which the first acoustic signal Lin is to be output and a position from which the second acoustic signal Rin is to be output is included in the first acoustic signal Lin and the second acoustic signal Rin, based on a result of a comparison between: - the signal level of at least one of the first acoustic signal Lin and the second acoustic signal Rin before the calculation; - and a result of the calculation; - the signal level of at least one of the first acoustic signal Lin and the second acoustic signal Rin before the calculation; - and a result of the calculation; the signal processing device further comprising: a signal generating unit which is configured to generate the third acoustic signal from the first acoustic signal Lin and the second acoustic signal Rin when the determining unit determines that the component of the third acoustic signal is included in the first acoustic signal Lin and the second acoustic signal Rin; wherein the determining unit is configured to determine that the component of the third acoustic signal is included in the first acoustic signal Lin and the second acoustic signal Rin when at least one condition of four conditions represented by (Lin + Rin) > Lin, (Lin + Rin) > Rin, (Lin - Rin) < Lin and (Lin - Rin) < Rin are satisfied; wherein the values of Lin, Rin, (Lin + Rin), (Lin - Rin) are absolute values, and Lin, Rin being amplitude values of the first and the second acoustic signals. a signal generating unit which is configured to generate the third acoustic signal from the first acoustic signal Lin and the second acoustic signal Rin when the determining unit determines that the component of the third acoustic signal is included in the first acoustic signal Lin and the second acoustic signal Rin; wherein the determining unit is configured to determine that the component of the third acoustic signal is included in the first acoustic signal Lin and the second acoustic signal Rin when at least one condition of four conditions represented by (Lin + Rin) > Lin, (Lin + Rin) > Rin, (Lin - Rin) < Lin and (Lin - Rin) < Rin are satisfied; wherein the values of Lin, Rin, (Lin + Rin), (Lin - Rin) are absolute values, and Lin, Rin being amplitude values of the first and the second acoustic signals.