There is a passage in Bermudo which seems to refer to the use of some sort
of device to raise the strings of the vihuela a semitone or a tone. It is
in Book 2, Chapter 36 f.30. It is referred to as a "panezuelo" which
literally seems to mean a handkerchief but there is some doubt as to whether
this is really what it means. He says that experienced players place this
under the strings close to the nut (pontezuela) and this rasies the pitch of
the strings.
Maybe someone more of an expert on Bermudo can elucidate.
Monica