When I bought my first 7 string guitar a few years ago I was expecting it to be a smooth graduation from six to seven strings. It took a few weeks to become able to actually just ignore that extra string and play regular six string guitar music. Slowly I started incorporating some of the lower notes but for a long time it felt more like 6+1 strings. Jazz shell voicings were the next big step. Walking bass lines. Reading cello music at least gave some workout for that extra low string. But somehow I couldn't find much music specifically written for seven string guitar - music that requires that low B string. Music that can't really be played on a regular guitar.
Like Bach's Two Part Inventions the music in The Well Tempered Clavier is timeless and even more so NOT for guitar. In other words: A good target for a seven string adaptation. Bach's original Well Tempered Clavier covers 48 pieces total in about 110 pages (at least in the piano edition I used.) As you can see with all the extra stuff we need that space for only the first six preludes and fugues. So it comes in four volumes just to keep everything a little more compact.
While it was relatively clear how to adapt the preludes to seven string guitar the fugues were a real challenge. I started with finding a 'good' key. Of course a purist will already criticize the key changes and I somewhat agree because my treatments just don't cover all the keys as the originals do. At the same time keeping the range of the piece inside the range of the instrument seemed more important to make it at least theoretically playable.
The bigger problem though was how to actually write out a fugue with three or four parts in a single staff system. When I put the original fugues into Finale on two staves it was often hard enough. After transposing into the preferred key and showing both staves with a guitar treble clef I could sort of sight read from this version. This is what you see below all but one of the fugues in smaller print. What you can see in the single main staff line is a brutal 'attack-only' version. It shows really only when to pick the given note(s) but not how long to hold them. And there goes all the counterpoint and the magic of the fugue. It is turned into a complex voice leading exercise! It's also hard to read in the context of standard classical guitar notation where you usually see notes picked with the thumb notated stem down and the others stem up.
This sounds like a list of reasons for not pursuing this project. But, after preparing the first fugue as a test subject, I found I really liked working it on the instrument. And while editing I started to hear the counterpoint in many places even though I only read from the single-staff version. And with the two-staff version shown just below the main staff all the counterpoint information is there.
While this material is pretty far removed from the ordinary classical guitar repertoire I feel I have reached my goal of presenting music that is both a challenge for sightreading and finger flexibility, and also rather specific for seven string guitar.
Lastly, I never liked to deal with guitar tab unless absolutely necessary. On these pieces though, when I tried to decide how much fingering information should be written in, I noticed that the right amount would have really cluttered up the standard notation. It seemed better to add a TAB staff. One of the most annoying features about tab is that you need a lot more pages. I decided to use up even more space and provide two versions: one in just standard notation, the other with standard and tab notations. I tried to write the 'easiest' fingerings down (but 'easy' is somewhat misleading in this context.)
Obviously, you don't have to print the TAB versions if you don't need them.