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Updating LED brightness values for velocity sensitive pads on the
Maschine leads to a perceived slowdown.  snd_ctl_elem_write appears to
be the culprit: new EV_ABS events are generated before the write
operation can complete, leading to a queue of writes.  Since, for the
Maschine, this involves rescaling input values (0 to 4096) to the LED
range of 0 to 63, we are potentially writing the same value
repeatedly.  By filtering out same-value writes, we can significantly
reduce the number of writes and thereby increase performance.

connect-control's abuse of keyword arguments needed a "dummy" keyword.
An empty list of keywords with only a #:rest section is not permitted.

by ALSA