In performance, Callas's vocal range was just short of three octaves, from F-sharp (F3) below middle C (C4) heard in "Arrigo! Ah parli a un core" from "I vespri siciliani" to E-natural (E6) above high C (C6), heard in the aria "Mercè, dilette amiche" in the final act of the same opera, as well as in Rossini's "Armida" and "Lakmé"s Bell Song. Whether or not Callas ever sang a high F-natural in performance has been open to debate. After her June 11, 1951, concert in Florence, Rock Ferris of "Musical Courier" said, "Her high E's and F's are taken full voice." Although no definite recording of Callas singing high Fs has surfaced, the presumed E-natural at the end of Rossini's "Armida"—a poor-quality bootleg recording of uncertain pitch—has been referred to as a high F by Italian musicologists and critics Eugenio Gara and Rodolfo Celletti. Callas expert Dr. Robert Seletsky, however, stated that since the finale of "Armida" is in the key of E, the final note could not have been an F, as it would have been dissonant. Author Eve Ruggieri has referred to the penultimate note in "Mercè, dilette amiche" from the 1951 Florence performances of "I vespri siciliani" as a high F; however, this claim is refuted by John Ardoin's review of the live recording of the performance as well as by the review of the recording in "Opera News", both of which refer to the note as a high E-natural.