Nantonos

This is an OS MIDI 2.0 implementation, looking for a MIDI 2.0 device, failing, and falling back to MIDI 1.0 as required by the spec.

There is now at least one MIDI 2.0 product (Roland A-88MKII, with revision 2 firmware). However this is a high-end product (hammer-action 88-key keyboard, for example) at a correspondingly high-end price ($1,266.99 at Sweetwater). (I do...

You could put a powered USB hub inside your case and connect that to the one Teensy USB Host port.

From the Pinout Card, the max current draw is 250mA. So you can draw up to 10mA per pin, but not from all pins simultaneously. And preferably, you would draw 4mA or less from each pin.

SPICE models for the Teensy4 ADC Input @MarkT - this addresses the points you raised, I hope. The last figure I think might explain why that sampling cap is only 2pf, besides that it is only 12 bits. The Teensy3.2 had 10pf for 16 bit mode...

Quick followup, O_C T4.1 is now in beta testing. Here's a photo of one of the beta test units being calibrated. Full open source release is likely soon, of course depending on feedback from beta testers in the coming days. But so far...