This essay (a translated, updated version of the last chapter of my book, Leopardi Sublime: la poetica della temporalità) examines Leopardi's conception of the role of sound as a major poetic device (a figure of sound). His writings on how sound produces poetic meaning and affect, scattered throughout his notebooks, Lo Zibaldone, have much in common with later 19th and 20th century poetic and linguistic investigations into what Roman Jakobson will call "the poetic function" or the paradigmatic axis of language use. For Leopardi, sound produces meaning in a more direct (or non-mimetic) mode than lexemes, and is inherently connected to his theories of the indefinite, memory and recurrence, and "il vago." The recurrence of a sound is therefore both the subject of many of his idilli and also a principle structuring device. In the concluding section, the essay turns to to Paul Valéry's theories of poetic sound, and to several lyrics of William Wordsworth, in order to initiate a possible "conversation" between these three poets.