Notice that Pizzarelli plays the 7-string guitar. Jazz legend George Van Epps is probably best known for utilizing this configuration. He had Epiphone build him a custom guitar in the 1930s and Gretch made a special edition for him in the 60s and 70s.
The rockers decided to experiment with 7 strings in the 80s. The added string was a high A, so the highest two and the lowest two strings were the same pitch two octaves apart.
Alex Gregory had Fender make a prototype 7-string Stratocaster for him and a couple of them were shown at the NAMM show in 1987, but Fender never put them into general production.
The Ibanez UV7 was adopted by Steve Vai while he was with Whitesnake. Since the High A tended to break too easily, the guitar featured a low B. He featured the instrument on his 1990 album Passion And Warfare.
Korn, Rush and Metallica are other bands who featured 7-string guitars.
Legendary 12-string player Roger McGuinn of the Byrds developed a 7-string folk guitar which is now in production by Martin. It features a double G string — same as a 12-string guitar — but all the rest are single strings.
Russian and Brazillian musicians and luthiers have developed and utilized the 7 string guitar for about 100 years.
