Relative tuning involves using one string as a reference to tune the other strings of your banjo. That string doesn't really have to be in tune with any outside source, because in this case, you're just getting the banjo strings in tune with one another so that you can play by yourself.
With each new string you tune in relative tuning, you then fret that string to create a new reference note that you use to tune the next highest string. Relative tuning is the most useful way to tune the banjo, because you need nothing but your banjo and your ears to get your instrument in tune. You have a banjo; now you can get to work on training your ears!
Even pro players follow up on their initial pass at relative tuning by trying different pairs of strings to hear what they sound like together and tuning the adjacent pairs of strings a second time. If one or more strings are severely out of tune to begin with, you definitely need to repeat the processes I describe in the following sections once or twice until the banjo is in good tune.
When tuning from low to high, you begin with the lowest-pitched 4th string and work your way up to the 5th string, the highest-pitched string. Using the following instructions, you tune the remaining four strings up from the 4th string, using the left-hand middle finger to fret each reference note. For now, try striking (or picking) each string with a downward motion of your right-hand thumb.
When you're comparing the pitches of two strings as you work through the following steps, your goal is to match the pitch of the open string to the fretted string that you pick. If the open string sounds higher in pitch, that string is sharp, and you want to adjust the tuning peg for that string in the direction that brings its pitch down (usually clockwise for the 3rd and 4th strings; counterclockwise for the 1st and 2nd strings).
If the open string is lower in pitch, that string is flat; in this case, you rotate the peg in the direction that causes the pitch of the string to rise (usually counterclockwise for the 3rd and 4th strings; clockwise for the 1st and 2nd strings).
Pick the 4th string fretted at the 5th fret and compare its pitch to the open 3rd string.
You may need to strike the fretted 4th string first, wait a moment to hear its pitch, and then strike the 3rd string to listen to its pitch. Does the 3rd string (the second note you play) sound higher or lower than the 4th string? Try singing the two pitches to feel whether the pitch rises or falls.
Using the tuning peg, adjust the pitch of the 3rd string up or down until it matches the pitch of the fretted 4th string.
When the pitches of the two strings match each other, the 4th and 3rd strings of your banjo are in tune.
Pick the 3rd string fretted at the 4th fret and match the open 2nd string to this sound.
After these strings sound the same, you have the 4th, 3rd, and 2nd strings of your banjo in tune.
Pick the 2nd string fretted at the 3rd fret and tune the open 1st string to this sound.
Pick the 1st string fretted at the 5th fret and tune the open 5th string to this sound.
Remember that the 5th string is the short string on your banjo that's located on the opposite side of your neck from the 1st string. Some banjos have 5th-string tuning pegs that are difficult to turn without causing wild fluctuations in pitch. Don't worry if it takes a bit more time to get the 5th string in tune.
Even if you follow these instructions carefully, you might discover the following frustrations when tuning the banjo in this way (but don't “fret” — you aren't alone):
Your reference point is always a fretted string when tuning from a lower- to a higher-pitched string. You need to lift the left hand up to adjust the tuning peg of the string you're attempting to tune and then fret it again on the lower string to play the reference pitch.
If you make a slight error at the beginning of this process, that mistake is exaggerated as you proceed to try and tune the rest of the strings. You might have to start all over.
If you're having difficulty determining whether a string is sharp or flat, tune it down until the string is obviously below the pitch of your reference note. Then gradually bring the string you're trying to get in tune up in pitch to match the reference note.