It is a work of nostalgia, a lament for the decline of steam engines - the stillness of the whistle. Based mainly on a poem by the Spanish writer, Gregorio Corral.
The setting is for twelve voices, eight of them singing through close microphones. The work is fourth in a series of pieces derived from 13th Century homophonic Spanish cantigas and canciones. The final series of works will form a sort of song-book, the composer's own accounts of early Spanish music. The idea of a song-book is contained in the title of the firstwork of the series, Cancionero para una mariposa.