Title : Sergei Rachmaninov, Vocalise (Songs (14), Op. 34: no 14)
From Wikipedia,Vocalise, Op. 34 No. 14 is a song by Sergei Rachmaninoff, published in 1912 as the last of his Fourteen Songs, Opus 34. Written for voice (soprano or tenor) with piano accompaniment, it contains no words, but is sung using any one vowel (of the singer’s choosing). It was dedicated to soprano Antonina Nezhdanova.
Although the original publication stipulates that the song may be sung by either soprano or tenor voice, it is usually chosen to be performed by a soprano. As with many classical vocal pieces, it is transcribed in a variety of keys, allowing the performer to choose a vocal range more suitable to their natural voice, so that artists who may not have the higher range of a soprano can nevertheless perform the song. When sung by a tenor, it is sung an octave lower than the same key when sung by a soprano.