Midi clock jitter from computers and DAWs is a very pervasive problem. The source of the problem is that your computer doesn't prioritize the midi data very highly (like it does with the audio data) so the midi clock, which is supposed to transmit 24 pulses per quarter note at a very steady pace actually transmits 24 pulses per quarter note, but the timing is all over the place. If you sync the H9 to Midi Clock we have some very good filtering available to extract a very accurate tempo BPM from even a very jittery midi clock, but in the process the location of the midi pulses is lost. We could re-generate them, but we still wouldn't know exactly where they were supposed to be in the original recording. The upshot is, if you need actual timing data from a crapppy source, and not just the average BPM value, you're hosed.
However, because this is a common problem a couple companies make little devices which transmit the midi clock on an audio channel, which your computer does treat as very high priority, and is therefore very accurate. Here are a couple examples:
Another option many people use is an external midi clock source. I personally use a drum machine as the midi clock source and slave my DAW to that, along with the H9 and other midi gear.Show More...
Here's another thread on the topic: