On a monophonic synth, or a polyphonic synth in unison mode, the procedure used to determine which note is actually sounded when more than one note is played on the keyboard. Three common methods are low-note priority, in which the lowest-pitched note being held is sounded; high-note priority is analagous, and last-note priority, in which the most recently struck note is sounded. High-note priority is generally regarded as the most useful; among other things, it can be used to emulate a guitarist's "hammer" technique by holding a low note and rapidly striking and releasing higher notes.
On a well-designed keyboard that employs resistor ladder circuitry, a note priority arbitrating circuit is an essential feature. Many performers will, when playing fast runs, employ a "passing" technique where two notes are held for a brief instant as the performer moves up or down the scale. If the resistor ladder lacked a priority mechanism, then during the period where two keys are pressed, the "sum of reciprocals" rule for resistors would cause the ladder circuit to produce a much lower or higher control voltage than intended, causing the VCO being controlled to output a frequency glitch.