The "Double" consists of two banjos playing together, side by side, operated by the same music roll, with each playing identical notes. This double arrangement tends to produce a "fuller" sound than just a single banjo, due to the slight dissonance that always exists between the two instruments. Bad tuning is not the question here, because no amount of careful tuning will keep the two instruments in perfect tune. This slight dissonance between the two is actually desirable, and, in fact, a slight tuned "beating" between pipe voices in band organs and orchestrions is deliberate, and is what gives them their characteristic full throated quality of sound.