Her voice sounds beautiful.
His eyes look frightening.
Your cooking smells fabulous!
I each of these examples, there is a noun preceded by a possessive adjective. Each states simply, whose voice, eyes, or cooking we mean.
The sound of her voice Is beautiful.
The look in his eyes is frightening.
The smell of your cooking is fabulous!
In each of the previous 3 examples, the possessive adjective still states whose eyes, voice, or cooking we mean but we have changed the initial verb into a noun. Then the preposition is added to the possessive adjective and noun to create the prepositional phrase.
It could be looked at as a more poetic way of speaking or writing. They both mean the same thing. However, if you don't insert a preposition in each of the second three examples, you do not have a complete thought/sentence. Hope this helps.