It is evident from the above definition that the Sha’riah does not forbid ‘pleasant sounds’; but if someone recites any thing with prolongation of sound and variation of pitch so much so that a common man thinks that he/she is singing, then and only then it will be ‘Ghina’ and sin
Music, according to the New National Dictionary, means "Art of combining sounds or sequences of notes into harmonious patterns pleasing to the ear and satisfying to the emotions; melody". According to the Great Encyclopaedic Dictionary, this combining of sounds is "for reproduction by the voice or various kinds of musical instruments in rhythmic, melodious and harmonious form so as to express thought or feeling and affect the emotion;" and the word is also used for the "sound so produced," and for ‘written or printed score of musical compositions." Not so technically, it is also used for "pleasant sound, e.g., song of a bird, murmur of a stream, cry of hounds."
In Islam some kind of music is called Ghina, and in Shia Sha’riah is counted as one of the ‘great sins’. At first, it may seem unrealistic to ban every "pleasant sound"; but there is no need to be alarmed. The Sha’riah has defined ‘Ghina’ in a different way. In Islam, vocal music means: "Prolongation and vibration of sound with variation of the pitch to such an extent that people may say that ‘he/she is singing’."
It is evident from the above definition that the Sha’riah does not forbid ‘pleasant sounds’; but if someone recites any thing with prolongation of sound and variation of pitch so much so that a common man thinks that he/she is singing, then and only then it will be ‘Ghina’ and sin.
And it makes no difference whether the recited thing is Qur’an, religious poem or love song.
Source: http://www.al-islam.org