Nonlinear interaction between pulses can severely reduce the bit-rate of an optical communication system. One way of reducing this interaction is amplitude shifting of consequtive pulses. In the present work a detailed analytical and numerical investigation is made of the coherent and incoherent interactions between two soliton pulses of unequal amplitudes. For the case of coherent interaction the obtained expressions for the pulse parameters in terms of initial phase and amplitude differences give a clear and explicit prediction of the reduction of the interaction strength for unequal soliton amplitudes. A comparison with numerical simulation results shows good agreement. For the case of incoherent soliton interaction it is found that the dependence of the interaction strength on the amplitude difference is weak.