In order to better understand the role of a banjo player in a band, one must understand the general roles of a band. There are generally two sections, vocals and instruments. Even groups that only technically have one of the two have aspects will have elements of both.
The difference within vocals is fairly simple. One or more persons sing melody and one or more other vocalists sing harmony (for a brief explanation of harmony, follow this video, just try to ignore the goofy hat). With instruments, the distinctions aren’t quite as easy. There are three categories; the melody, the harmony, and the rhythm. Generally, the melody instrument is a guitar or a fiddle. The melody strums the chords, plays the main riff, or plays the melody line, this is generally done by the lead instrument, which is generally a guitar, fiddle, or banjo (but can be any melodic instrument). In this example video, the fiddle plays the melody riff. On top of this, there are generally harmony instruments. These include backing guitars, backing banjos, and other backing instruments. In the above video, the banjo and cello play a harmony to the fiddle’s melody. The harmony instruments help fill out a song and provide greater depth. The rhythm section includes bass, drums/percussion, and sometimes cello. This section is often crucial to keeping all the other instruments in time. Along with the harmony instruments, the rhythm fills out songs and keeps everything even.
So where do you fit in? It depends on what your band needs. If you have a solid rhythm section, then maybe you should play melody. If you have a solid lead guitarist, then maybe you should play more harmony. If you have three fiddles that can’t stay on time, maybe rhythm is the best option. You also need to know what you are strongest at. If you struggle to keep a beat, maybe harmony or melody would be better. If you are rock solid, but don’t like improvising or deviating, rhythm might be best for you. If you enjoy playing chords, and don’t really want to move from that, harmony would be your best option.
That being said, sometimes the best option can be having fluid roles. Playing just one section can be uplifting, or it can be boring, depending on the skill level of the individual and their idea of playing music. In my band, we switch things up almost every song. One song I will be singing harmony, another I will be playing melody on the banjo and singing melody, and another I will play banjo in a rhythm sense, only playing constant notes and not deviating from that.
In my experience, the banjo can play in most songs. Generally I don’t play the banjo in slow, sad songs, or cover songs that have distinct instrumentation. Other than that, I play banjo all the time in my band. When I am playing rhythm, I roll a constant pattern of notes. Playing what comes easy is best when it comes to rhythm, since your role is to support the other instruments. When I am playing harmony, I tend to take rests (really really short pauses), play chords higher up the neck, or experiment with the timing on a song. When I play melody, I usually am doing it for a song I wrote, so I will play the riff or chords that I have memorized.
The best way to find what role suits you is to play your banjo. There is no better way to determine your role with your band than to practice together and see what works. Try switching things around and experimenting. Experience is the best teacher in this case. As always, happy picking!
Footnote 1: For example, many A Capella groups will have a beat-boxer, and almost all have a bass vocalist that sings something similar to a bass guitar. This group is a good example of both concepts, link. Also, instrumental groups will often have a single instrument play a melody line, similar to a single vocalist singing the melody of a song. Béla Fleck is a pristine instance of this in a excellent song. Notice how all the instruments come together to form the chorus.