Definition of "purring"

Kenny G is a dull but wickedly consistent musician: automatic with his tremulous phrasing and canned licks, which formed fast, organized roils during his unaccompanied solos; melismatic purrings of the melody on ballads; and gospel phrases in R&B songs.

2008 February 14, Ben Ratliff, “Upholding the Standards of Smooth Jazz Purists”, in New York Times‎