 Peter OToole (I) (qv) recorded his vocal tracks for the film, but  realized that his own singing voice was not good enough for the  requirements of the music, so he assisted in the search for a voice  double. The man OToole picked sounded nothing like him, so a new  search was begun, and eventually Simon Gilbert (I) (qv) was  selected as the singing voice of Don Quixote, because his singing  voice sounded the most like OTooles speaking voice.