I just tried controlling my boss dr-770 drum machine with a step sequencer in Pd and when I get it going the audio sounds kinda phasey. It is coming directly out of the drum machine like that, and it only sounds that way when I have the sequencer playing. If I stop it and just hit the pads the sound is normal...

I'm guessing it is some sort of timing issue, but I have never heard of midi control effecting the sound of a device like that. I went through all the midi settings on the machine to see if I could correct it but no luck.

I've found when using drum samplers a phasing/comb filtered sound usually means a note-on is being triggered twice. MIDI take about a millisecond to transmit a single message, so if you have two note-ons scheduled to be triggered at the same time, there will actually be a one millisecond delay, causing some comb filtering. I don't know anything about the dr-770, but I would check to see if either your patch is double-triggering or if the dr-770 is set to multiply the MIDI messages. Maybe something like an omni mode?

OK. That sounds logical. But exactly how could I determine if this is what is happening?

You can try attaching a counter object to it and see if it outputs by multiples of 2 instead 1. Not sure if it'll actually work though.

Or just attach a [print] before the [noteout] or whatever you're using. If everything shows up twice, it's a problem with your patch.