theoretically, what all mahiiiji said is absolutely right.in simple language to say,when we hear sanjeev kumar singing meri bheegi bheegi si palkho me rehgayi, song from the movie anamika,or when rajesh khanna singing roop tera mastana,or when amitabh singing dilbhar mere,or for that matter kaante nahi kathe din ye raat by anil kapoor,we feel they them selves are singing,it is them nd no one .but the playback given by kishore da
we should feel the actor himself is singing.
when sreeram sang kawa kawa, I felt some punjabi singer is singing,as I heard it from the other room, nd when I saw the video,I couldnt believe how he modified his voice as per the song .this is called versatile singing.this is what they are indeed looking this year in indian idol 5.versatality,playback voice.