The lowest acceptable PPQ is 96. Ideally you want a sequencer with the highest PPQ resolution available. A higher resolution does allow you to more accurately offset the parameters of tools that allow you to alter the MIDI data in relation to time. Cakewalk Home Studio Try not to use quantinization too much, however. It is the timing irregularities we humans introduce to music that prevents it all from sounding like it was created by a machine.
Nobody has the kind of perfect timing a computer has - so, quantize sparingly.
To play back a sequence, most MIDI sequencers default to their internal clock. If you have a secondary MIDI device that you record information into, such as a drum machine, you can make the MIDI sequencer sync to the MIDI clock output of the external device or vice versa. Using this method, you can control the playback of externally recorded MIDI data from a single set of controls. More than one point of timing reference can create some very weird music. Not very pleasant, unless you are into that sort of thing, or you're using hallucinogenic chemicals.