Polyend Tracker clock issue/mystery


I’m trying to use the Polyend Tracker as a clock source into the FLXS1’s 3.5mm MIDI In port and found the FLXS1 wouldn’t respond at all.

I verified the Tracker is configured and sending everything correctly with MIDI Monitor on OS X — it’s sending 0xFA, 0xF8, and 0xFC bytes for Start, Clock, and Stop respectively (and Ableton is able to sync to it successfully).

I verified all my Type A and Type B 3.5mm->MIDI adapters were correct, and confirmed that FLXS1 happily syncs via 3.5mm MIDI to e.g. Ableton Live sending to an external USB MIDI interface.

I then built the FLXS1 source repository to connect and debug via serial. I added a Serial.printf here https://github.com/cosmikwolf/FLXS1/blob/master/lib/MIDI/src/MIDI.hpp#L691 and found that the bytes from the Tracker are, quite mystifyingly, coming in as 0xF0 (i.e. Sysex Start) where 0xF8 (Clock) should be, and 0xF8 (Clock) where 0xFC (Stop) should be. Other MIDI messages like note on look similarly corrupted. Checking Ableton’s clock messages in this manner shows everything coming up correctly (FA, F8, FC, all report correctly and work great) (again, using the same 3.5mm MIDI In port).

I can swap MIDI cables on the fly while logging and see the good clock messages coming from Ableton, and the bad clock messages coming from the Tracker, and again, can also plug the Tracker into other MIDI gear and they see the messages as AOK and respond as such. So this really seems to be some specific issue with FLXS1 and the Tracker specifically.

Oh, and just flailing, I also tried powering the Tracker via a USB battery in case is some weird grounding issue, but no luck there either.

I’m at a bit of a loss now — @tenkai any ideas what could cause this??

All the best


Hey Luke,

Sorry for the late response. I had been on another planet for a little while.

This is indeed curious. Good on you for inspecting the serial traffic!

Strange as it sounds, I have had a faulty midi cable adapter cause weird issues like this, so that is something to suspect. I would make sure the contacts are all clean. Try a different adapter and midi cable if you have one.

It does sound like it could be some strange isolation issue. Possibly connecting through another device using Midi Thru to see if it would retransmit properly?

Are you able to get your FLXS1 to sync properly with other devices via 3.5mm midi?