A standard 5 string banjo is often tuned to Open G (gDgbd). Disregarding the high drone g string, using a 4 string CBG, I usually use Dgbd tuning (CD 5). This is also the highest strings of the full 6 string tuning on guitar for Open G - DGDgbd (CD 2).
This banjo simply reduces the standard banjo tuning down by elimating the two highest strings. gDgbd into gDg. I use this GDg tuning on 3 string CBG too (CD 4). The only difference is the (banjo) tone created by having a high drone g instead of a lower g on CBG.
(Note: I am tuned up a full step to aEa on this banjo. Due to the fact the relationships between the strings are staying the same, all the finger positions will be the same.) A fundamental understanding of musical theory can go a long way to seeing the various possibilities of playing in different keys. (CD 7)
In a future video, I will present a more traditional approach by alternating the high drone a and E strings while playing a melody line on the first a string. Keep in mind, 5 string banjos are usually fingerpicked (Earl Scruggs 3 finger style) or use the claw hammer method. 4 string tenor or plectrum banjos are played with a flat pick.
Another interesting possibility would be an altered 4 string banjo. A high g drone and Dgb. Dgb is the same string relationship from the major scale (513) as the ADf# tuning I use on CD 6 for 3 string CBG. Using the movable chord method that this tuning offers could make for a very versatile instrument. (Note: This instrument could be tuned up a whole step to aEac# and all the fingering positions would remain the same.)
Enjoy your practice. http://youtu.be/o8PKhCCcA44