Vocalise" Op. 34-14 is the last of 14 songs in Rachmaninoff's Op. 34, which was sung only in vowels. It's a beautiful melody that purifies your heart when performing and listening to it.
Don't get too caught up in the tempo of the trills that contain the phrases and the agogics that accompany the crescendos (but don't forget to balance them) so that they remain beautiful and musical. It is also important to embrace the melody line and set the singing style for each player. Naturally, the tone will change if the instrument changes, but study pitch and vibrato properties so that they are expressed as similarly as possible.