Who is the 'telling voice'?

As everybody already knows who reads this; Don Quijote is a very complex work. There is something I've been thinking about: who is the telling voice?
Is it Cervantes or another person? As I understand it we can gather there is almost a 'poetic Cervantes', a bit like Dante uses for his Comedia, who is telling the story? But he in his turn has found the story through a third source, such as the Arab man who sells some pages to him? Then we also have Don Quijote himself at some points acting as Cervantes medium to convey the real Cervantes' voice, not the poetic Cervantes? Is this something you can agree upon?

I certainly agree that Don Quixote, as well as most of the characters, are used to voice/demonstrate the author's views and ideas. In general in fiction, characters are used to demonstrate a given idea, either positively or negatively.

In answer to your question on the 'telling voice,' the fictional context within this book is that a Moorish historian and writer named Cide Hamete Benengeli (again, fictional) documented Don Quixote's life. Then, the character that you refer to as "poetic Cervantes," the Cervantes within the book, collects the historical manuscripts written by Benengeli and translates them into Spanish to write the book we are reading.

Cervantes (the actual author) uses this self-referential approach to comment on authorship itself and (through Benengeli's excessive interjection of opinions into his 'historical' writing) criticizes the tenancy for historians of Cervantes' time to embellish their writing to make it more interesting and story-like.