16GB om Memory is quite a lot and should be fine unless you have big sessions of Play or Vienna Instrument loaded in your Project.
To check what is going on with your memory and how it is used, optn the utility app "Activity Monitor". It is located in the /Applications/Utilities folder.
Here you see all the apps that ar currently running and their stats regarding CPU and Memory allocation.
Also selct the "System Memory" tab at the bottom to see the overal situaion of your RAM.
- Total installed RAM. See if your system sees all the 16GB
- How much REAL Memory is currently used.
- Check the Page Outs and the Swap space. If you are running a lot of apps (or Safari with a lot of tabs), your system will fall back on "virtual Memory" which means it outseources the storage to your (slower) drive. This is not good, especially for realtime apps
Keep that Activity Monitor window open and see how how your memory usage goes up with each instrument you load in GarageBand. Maybe there is a "bad one" that gobbles up all your memory.
Here is a screenshot of the Activity MonitorHope that helps
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