First of all when two waves pass each other they dont reaĺly combine into one wave ,it is the particle in that region that displaces itself according to the sum of displacement of two waves at that point. So a wave should be unchanged at all time and reach reciever unaffected. but if it is that reciever reads resultant wave so both amplitude and frequency should be affected .why frequency is not affected in any modulation ? I have seen superpositions of two wave of different frequencies and the resultant frequency is different .