Triggering arpeggiator with a melody line

[SGuttman]

For live performance, I'm trying to create a setup whereby I use a mono melody track to run thru the scale and chord midi effects into an arp (either the midi effect or an arp preset in a vst). Are there any Max plugins that can isolate an incoming note on the basis of position in the bar, e.g. the first note of a bar to generate the chord and hold it throughout the bar, ignoring the subsequent notes, which otherwise keep re-triggering the arp? This way I only have to make sure that the first note of the bar is the root note of the chord I want held for the remainder of the bar, Any ideas, or a way to do something similar?

[anamexis]

You could do this without M4L by automating the chain selector of a MIDI FX rack so that MIDI is sent to the Arp only on the first beat of a measure, and then setting the Arpeggiator "Hold" to on

[SGuttman]

That sounds interesting. How would you automate the chain selector?

[anamexis]

Normal clip automation (or modulation if you don't have Live 9)