First of all, I'm a drummer and I use a drumpad(DrumKat) to trigger samples on my laptop, so for me the latency is a 1st class problem.
I have two setups: one with Ubuntu 10.04(Kernel 2.6.33-29-realtime) + jack, and the other with OSX leopard + jackosx. The first one is the more tested.

I want to know the latency that PD creates between notein-noteout process.
To do this, I simply connected my drumpad to PD's midiin, PD's midiout to PD's midiin, and opened my patch(attached to this post).

If the patch is right, there is a link between jack's latency and PD's MIDI latency.
If I set jack's framebuffer to 256, I have 11.6 msec of audio latency and 5.8 ms of PD's MIDI latency.
If I set jack's framebuffer to 128, I have 5.8 msec of audio latency and 2.9 ms of PD's MIDI latency.

Is this correct? Is there a way to reduce MIDI latency without changing the audio latency of jack?

Thank you and sorry for my english.

Nicola

http://www.pdpatchrepo.info/hurleur/pd-midi_latency_test.pd

But anyway, to reduce the latency you'll need to reduce Pd's latency in the audio settings dialog as low as you can get it. If you're just doing MIDI processing (i.e. [notein] -> process -> [noteout]), you can run that in it's own instance of Pd and reduce the audio buffer to a minimum. Then have the audio stuff in its own instance.

As far as I know, this is only an issue with MIDI output. I don't think it's an issue with input, so if you're just triggering audio in Pd with MIDI and aren't sending MIDI events out, it shouldn't be something to worry about.

I've got a MIDI keyboard triggering samples in buffers. So there's a [notein] taking MIDI notes which are assigned with a [sel 1 2 3 4 etc] object to buffers which have little samples for each key in.

There is a considerable delay between pressing the key and hearing the sound.

I've also got a [key] object for using the computer keyboard to select the different sounds that go in to the buffers and there's an even larger delay between pressing the key and the sound changing.

Help!

Perhaps you were hoping for latency compensation?

I find 20ms the threshold for suitable keyboard playing.

And get Jack, though I don't know much about PD on windows other than that some people have reported impressively low latencies. Search the forum.

??