MARC21       007v'06  Medium for sound
     Values: 
              #   No sound (silent)
              a   Optical sound track on motion picture film
              b   Magnetic sound track on motion picture film
              c   Magnetic audio tape in cartridge
              d   Sound disc
              e   Magnetic audio tape on reel
              f   Magnetic audio tape in cassette
              g   Optical and magnetic sound track on motion picture film
              h   Videotape
              i   Videodisc
              u   Unknown
              z   Other