Just a quick note...it's not easy to get the Alesis Performance Pad synced up with your Linux system. Jack and Ardour supports MTC, not midi clock (at least not yet).
My need was to sync all of my virtual stuff (seq24, Ardour) with my drum machine, the Alesis. Unfortunately, no midi in on the Alesis, only midi out. The Alesis will emit old school midi clock messages, and that's about it.
My hackish solution: use Rosegarden.
Under settings/midi/midi sync you'll find a MIDI Clock and System Messages option. From the drop down select "Accept start, stop and continue."
Assuming your external synth or drum machine is connected via midi in to jack, pressing play on the external device will now start Rosegarden. If synced to other Jack applications, this will also kick off your entire virtual orchestra.