Luis de Narváez was a Spanish 16th Century Renaissance composer who wrote extensively for the vihuela, a guitar-like instrument with double strings tuned like a lute in a slightly different way to the guitar. Although sometimes played on period instruments his music is now more frequently played on the guitar. "Diferencias sobre Guardame las Vacas" in English would translate something like "Variations on Guarding the Cows" where "Guarding the Cows" must be an existing folk melody. The piece is most commonly presented as a theme and 3 variations, and note that the 3rd variation is extended by a short coda to round off the pice. Sometimes however a further set of 4 variations are added. The video below illustrates the music in piano roll format, while below that you can play the mp3 file and see the music before downloading.