This article will almost certainly make more sense with accompanying videos. I plan to make those as soon as it is safe. (5-29-2020)
Rolls are the closest thing that marimba has to a sustain pedal. At times, a roll is needed but only one hand is available to perform it. In this case, it is possible to employ a one handed roll.
comfortable intervals
In the world of 4-mallet playing, not all intervals are created equal. This is especially true when playing one handed rolls. In my view, the mallets sit most comfortably around a 5th. (This of course is not a fixed size on an instrument with graduated bars). The farther away from a fifth, the less comfortable it is to play. After a certain point (no larger than a 10th), playing with two mallets in one hand is essentially impossible.
In the case of one handed rolls, I’d argue that small intervals are harder than (achievable) large ones. Small intervals prevent the proper torque needed to execute a quality roll. On the other hand, large intervals can risk the stability of the mallets and compromise the sound.
Generally speaking, the less comfortable the interval, the lower the dynamic ceiling, and with a lower dynamic ceiling comes a lower chance to make a good sound. Closer intervals allows for less torque in the wrist motion, meaning it’s not possible to play the keys as hard. Rolling on a single note is extremely uncomfortable, though may at some points be executed using a split roll (see below).
notation
In most cases, there is no need for special notation on one handed rolls. The one exception is if a composer wants both hands to roll with one hand simultaneously. If needed, a text instruction could due, or a specially notated stem. There is no standard for this, so whatever you choose should be specified in the performance notes.
playing between the roll
In some situations, it is possible for one hand to engage in a one handed roll while the other plays between the rolled notes. One instance of this is viewable in the below example:
In this instance, the right (rolling) hand will need to be set at an angle that leaves certain notes (in this example, C# and F#) available to be played.
split roll
The “split roll” refers to holding two mallets in one hand and rolling on a single note or surface by moving the hand vertically. This is achievable on most mallet instruments, but only on the natural keys when playing from the normal side of the instrument, as the accidentals will be blocked from this technique.
mallet choice
Keep in mind the consequences of mallet guidelines when writing for a one handed roll. Any chance of the roll sounding even will go right out the window if a hand is to be holding different types of mallets. For example, if one hand is required to hold one yarn and one plastic mallet, a one-handed roll will produce 2 starkly different attacks.
beyond keyboards
One handed rolls have uses beyond keyboards; it can be used on any instrument, with varying effectiveness. This does not need to be notated in any way, and is up to the player to determine how best to execute a passage.
Recommended Listening:
Chris Cerrone: Memory Palace (split roll)
Adam Holmes 