(It.: ‘to spin the sound/the voice/the tone’; Fr. filer le son).
A direction in singing to ‘spin out’ a long note, usually pianissimo, without any change in dynamics. Verdi uses this direction at the end of Violetta’s aria ‘Addio del passato’ in La traviata, where the phrase ‘un filo di voce’ is attached to the final a'', its soft dynamic emphasized by the preceding direction, allargando e morendo. At the end of the sleep-walking scene in Macbeth, Verdi uses this term over the final four notes, rising to d''', indicating that the phrase should be sung without a crescendo and, probably, with little or no vibrato.
The term is also used for wind instruments and (meaning without a change of bow) for string instruments, the direction usually implying that the note is to be sustained quietly and without any gradation in volume. L’Abbé le fils (J.-B. Saint-Sevin) defines the term this way in his Principes du violon (1761).
In both vocal and instrumental music the term has sometimes, confusingly, been equated with Son filé or Messa di voce.
ELLEN T. HARRIS