A freshman here. When I’m playing on my Yamaha MX88 or iRig Keys I/O plugged directly into my MacBook Pro i7 16 gb of ram, I’m experiencing such a lag that I’m unable to affectedly play without being too late/behind the beat. It doesn’t depend on which VST I use. Of course the MX88 plays fine as a stand alone (not plugged into GP). I have GP 4.5.8
What are some areas to troubleshoot?
Thanks
Make sure you are using the ASIO audio driver with a reasonable buffersize of <512
See:
Also make sure you’ve read the rest of the manual! 
You’ll find the link to the docs being permanently present in the top line of the forum site (if you are not surfing with your mobile).
Thanks for the quick response! Do I need an ASIO driver with a Mac? I have read parts of the manual and I’m sure I’m missing something big. I’ll change my buffer size and try it.
Can’t tell for sure… i am a Windows guy.
But just look if there is an ASIO item in the sound driver field, then simply try this to see if things are getting better.
It isn’t available. when I do audio support. I thought I saw where Apple doesn’t use or need an ASIO (no slam intended to Windows users. I will try and reset the buffers tho.
The lag will improve if you use a dedicated audio interface, not the built in input and output. To oversimplify, the interface will have faster drivers which will add less to the 11.6ms.
Meanwhile see if it all works at 256 or even 128
No ASIO on Mac (Core Audio is used). 
Yes, try setting the buffer size to 128 or 256.
Of course, get yourself an audio interface.
As others have noted, a dedicated audio interface, even an inexpensive one like the MOTU M2 will perform far better than the built in sound card.
And 512 samples buffer size is to high, try to lower it.
… I am running the whole band through 512ms buffer;
seems to work as nobody (drum, bass, guitar, vocals) was claiming the reaction time. Sure, less is better, but as “power user” you want to be on the safe side, to avoid cracks etc…
For sure, with a single instrument on a MAC, 128 should be no problem, with an audio interface.
You mentioned that you also own a iRig Keys I/O and i wonder why you don’t use this as a dedicated audio interface… at least this might something you could try as well.
…just in case that the Built-in soundchip won’t do as you want it to…
“Again what learned!” (as we Germans say) 
No, only Lothar says.
(Off topic) We (Dutch) say: “Weer wat geleerd”.
French could say: « je me coucherai moins con… »
Thanks, I used a Behringer U-PHORIA UMC404HD and tried it last night. it made a significant difference.
This is still my “spare-audio-interface”… it’s a solid device which i cannot complain about… never let me down. Unfortunately many people don’t trust the Behringer cheapos… but i own a lot of Behringer stuff and most of it is actually not bad!
I also like Behringer. Here is an anecdote about Behringer reliability from the latest stream with Jim Erwin → LINK
