[Ancient Geek]

To help see what's going on, if your 'scope supports it, try setting the timebase and trigger holdoff so that you can see a consistent trace when you repetitively hit a key. This would make it easier to see any noise or jitter. The timebase should be such that you see at least the whole first byte of data. There's one start bit, 8 data bits and a stop bit transmitted at 31250 bits per second. If my mental arithmetic is not way off beam, something like 25-50 microseconds per division horizontal timebase would work. The idea of the trigger holdoff is that it's a delay to prevent the scope from retriggering until after the end of the midi message to avoid the trace of the first byte or two being overwritten. You may need to adjust this. Try hitting the same key repetitively at a rate that allows you to see what's going on given the screen persistence of your scope. If you have it set up right, you should be able to see any changes in the status byte that contains the channel ID, and also any jitter in the bit timings.