Backup, "boom-chuck" guitar plays a bass note on the one and three, a chord on the two and four. Fine. What note?
The first beat of the measure is the note that names the chord, typically a D, G, A, C or E. These all lie in the bottom octave of the guitar. The only one not on the first two strings is the open, fourth-string, D, for the D chord.
The third beat of the measure is some other convenient string in the chord -- sometimes above, sometimes below -- also on these bottom three strings. I typically use D/A, G/B, A/E, C./G, and E/B in the five basic chords.
The "chuck" is a quick flick across the higher notes of the chord. (That's higher musically. The strings are closer to the ground. Confusingly, plucked instruments like guitar and mando number their strings starting nearest the ground, so the highest-pitched string is '1'. Banjos, even more confusingly, use that same rule, but the short, fifth string has the highest pitch.)
Emphasize the boom. The chuck doesn't need to be loud, just enough to be rhythmic and in a reasonable chord. Sandy Bradley said she used to come home after gigs with a black fingernail on her right hand. This stayed a mystery until she figured out she'd been chucking with the nail, not even the pick.
It's all downstrokes and root-position chords. If a guitar player is strumming hard and loud on each beat, with lots of upstrokes, you can bet this isn't his native, musical language.
(Rules are made to be broken. If someone's doing this and it sounds really great, he may be doing it on purpose, so watch for a couple of tunes before you judge.)
Each musical instrument has a native backup rhythm. Bluegrass, backup mandolin is all chucks on the two and four. Bass is all boom on the one and three. Banjo uke is all four plus the off-beats: chuck-a-chuck-a-chuck-a-chuck-chuck-a, like a machine. Banjo is bump-ti-ty. Tim Green says a Harley-Davidson is potato-potato-potato. I say, "That's not a musical instrument."
Tim says, "So? Neither is a banjo."
Mando in a contra or square-dance band? It's up to you. The instruments above have everything else covered, and I'm not trying to make the tune sound like it's bluegrass, so I'll try something different each tune, or even each time through, to color the tune and make it more danceable.
Tastes vary.
I went to a band workshop by Tom Adler, Alice Gerard, and Brad Leftwich, all spectacular musicians. They put us into bands and gave each band a tune to work up. Brad Leftwich came around, listened to us, stopped us, and said we all had the right idea, except me. A mandolin, he said, plays chuck-a-chuck-a through tunes, like a banjo uke. I'm easy and I did what I was told. He nodded approval and went on to fine-tune the next band.
"When you ask someone for advice, don't then argue with him about it," I always say.
The next time I was at a jam, I tried out my new skills. After the second tune, Dave Brown turned to me disapprovingly and said, "Could you play normal?"
