The song is described as "a series of deep booming notes, the first 3 rising, the last 2 even at a slightly higher pitch: BMMM mmMMM... mmMMM'BMMM-BMMM, sometimes followed after pause by sharp BMM!" (Lane, in Schulenberg et al. 2007). The song has a very low frequency, which renders it difficult to record well under field conditions. The song also is somewhat ventriloquial, and usually does not sound very low, even at close range.
The song usually is given from a perch, from a few m above the ground to the lower canopy (Gutiérrez 1997).
Singing is most frequent at or before dawn (03:00-05:00), but may take place at any time during the day, as well as throughout the night (Gutiérrez 1997, del Hoyo and Motis 2004). Song is rarely given when curassows are not breeding; for example, at one site in southeastern Peru no song was noted from March-July, a limited amount of singing was detected in August, song became frequent in September, and dropped off again in December (Gutiérrez 1997, del Hoyo and Motis 2004).
Calls of Razor-billed Curassow include "rising whistles and popping notes" (Lane, in Schulenberg et al. 2007) and "soft pweet calls" (O'Neill 1974).