The Roland SH-01A has an arpeggiator that only starts when more than one note are active at the same time. You can play monophonic without the arpeggiator turning your playing into a staccato.

This MIDI Rack tries to emulate this (and more).

Thanks @gravitas for the initial idea and for sharing the initial patch in the AudioBus Forum!

How does it work:
– The “Threshold” parameter sets the maximum number of voices that will be passed through the patch without arpeggiation. If it’s set to 3, you can play a triad, and the connected (polyphonic) synth will play a triad. Add another note, and the arp will start running. You will then get monophonic output.

– The “ARP” section is a standard Drambo MIDI arpeggiator.

– “Mode” allows for three operating modes:
RUN -> Always arpeggiate without threshold.
TH -> Only arpeggiate when the voice threshold is exceeded.
OFF -> Polyphonic passthru / no arpeggiation.

Changelog:
0.1 initial release.
0.2 fixed multiple note triggers in MIDI output.