Cause very important role intro (note tones) a song, every musician who created the music of the paper will be thinking very carefully with the concept or the tone that would mark the beginning of a song. Music because it will be very pitch-sugest mind to heed a song, if it is directly from the intro to enjoy it. then automatically will be very curious to gather from the entire song. Different if otherwise. if we have thinking to feel or hear the alert tone that weird or normal, ordinary course of a song intro, we can be directly turned to listen to the songs.
Not all the songs, that the tone at the beginning of the intro song. there is also a direct jump to the song's reff. there is also a take-tone Reff its opener to be a song. the master of his songs are ringing Reff is more easily recognizable (in mind) to poison it to music. in addition can also be used as an alternative as distinguish's songs, or just to be more varied. there is no rule that requires that every song must have its intro, but as a reality of life, intro is a "first impression". The first impression is the beginning of everything.
30 seconds at the beginning of the song is the determination of the entire song can be enjoyed or in the ear it is not music. if the first 30 seconds of a song can have direct steal music and attention it got a good appreciation, this is a benefit for musicians who created the song.