My problem is that when I press play on Bitwig, I get the MIDI notes to channel 1 going, or I assume, they are going to the correct channel, but I am not sure. If I arm any of the other tracks, I get a flashing quickly MIDI notes and then a PortMIDI: 'Buffer overflow' as shown in the jpeg.

Is there a simple way to use Bitwig or some other app to easily demo this type of Pd patch? I am kind of stuck with it and not sure how to proceed. Reading on has not helped resolve the issue.

If I arm any of the other tracks, I get a flashing quickly MIDI notes and then a PortMIDI: 'Buffer overflow' as shown in the jpeg.

By "arm," do you mean enable MIDI input on the Bitwig tracks?

If you're sending MIDI out from Bitwig, there shouldn't be any need to arm anything.

I'm guessing that you've got a MIDI feedback loop somewhere. For the Pd patch, MIDI should be traveling in only one direction: DAW --> IAC bus --> Pd. This Pd patch isn't sending MIDI out anywhere, so Pd can't be the source of the loop.

"PortMIDI: Buffer overflow" isn't a Pd internal error so you'll have to address it in the way MIDI is configured in your system (DAW and OS settings).

hjh

In a MIDI message, thestatus byte differentiates the various message types, with a leading 1 to indicate that it's a status byte, a 3-bit code for the message type and, for messages that apply to channels, a 4-bit channel code, packed together into one byte.

Binary 1 001 zzzz = hexadecimal 0x9z = note on
Binary 1 000 xxxx = hex 0x8z = note off
Etc (https://www.recordingblogs.com/wiki/status-byte-of-a-midi-message)

Note on messages on channel 1 should be encoded as 0x90 (decimal 144), on channel 2 as 0x91 (145), up to 0x9F (159) for channel 16.

So the MIDI channel information that pd receives is encoded into the message contents. The IAC bus, of course, shouldn't modify message contents! So the IAC bus is vanishingly unlikely as the cause of the problem.

Bitwig is responsible for encoding its outgoing MIDI messages, so if a wrong channel is being encoded, that's where it's happening. I'd suggest to doublecheck the outgoing MIDI channel assignment in the MIDI tracks in Bitwig. Also, in some DAWs, MIDI notes can have their own MIDI channel data; the track-level MIDI channel setting might override the note-level setting, or vice versa. You'd have to check documentation on that.

hjh