Most people associate the 8 string guitar with djent or micro-riffs (like Meshuggah or Dino Cazares), maybe even technical death metal (like Rivers of Nihil), but it can be much more than a low chugging metal machine. It can be tuned to produce a broader spectrum of sound by adding a high string and losing the low F# (which treads on the range of the bass guitar anyway), giving your chords more range and sparkle and giving you more options for counterpoint and high melody.
For anyone wanting to try my 8 string setup (which involves an extra high string and low string compared to standard guitar):
My guitar is tuned from the highest to lowest G-D-A-F-C-G-D-A. The string gauges I use are from D’Addario .08 .010 .013 .017 .026 .036 .046 .059 – This is semi-custom (there is not 8 string set that accommodates me) and can be recreated by buying a 7 string set of light gauge XL nickel-wound strings (“EXL 110-7” is the part number) and buying separate single high g strings (PL008).
There are a few ways to think about this tuning-
1) Renaissance Lute – This is the same as a popular 8 course renaissance lute tuning, and you can actually read a large selection of lute tablature on your 8 string guitar using this tuning and it will sound at pitch. Lots of classical guitarists are used to lute tuning (which is usually dropping the 3rd string to F#)
2) A 7 string guitar, dropped a whole step (2 frets) plus a high string. You can then think of the middle six strings as being like a standard guitar, and you have a high A and low B to work with – of course, you must transpose everything up a whole step to have the correct chord in reverence to a piano. This seems like a lot of thought, but it’s the most familiar way to approach the tuning.
Fun fact – This tuning puts your guitar into “Bb” transposition, meaning you can read music for trumpet, soprano and bass clarinet, soprano and alto sax. Bass Clarinet and Tenor sax will sound at pitch. All the others will sound an octave lower than written.
As for string choice, you are going to have limitations using a high G/A string. The D’Addario PL008 string, as well as the PL007 string, are both designed to sound at a “G” (the same as the third fret on the first string of the guitar) by being the upper octave of the third course (set of paired strings) of a 12 string guitar. I have tried tunings “in c” rather than Bb (essentially tuning that high string to an “A”) but the highest string is very brittle and will break frequently. Tuning it to G solves these problems, and it was only natural for me to follow suit with the rest of the strings. I normally play on .009 strings for my high E (ultra-light), so for every step I lower when tuning I size up the strings. You can use whatever strings you want for 2-8, but the 7 string sets that start with a .010 gauge string usually feel the best for me in this tuning, and I think that’s a great place to start.
By the way, Ihsahn plays with a more standard 8 string setup – high E to low F#.
Hope that helps!