El Capitan 10.11.6 and Logic pro 9.1.8 are they compatable?

El Capitan is a 64-bit only OS. The version of Logic Pro you have is 32-bit. I doubt it will run reliably. However, you will need to find out what the system requirements are for that version (I don't know.) The current version is 10.3. I suggest you upgrade your version. Also, see App Compatibility Table - RoaringApps.

You can boot Logic 9.1.8 in both 32 and 64bit. Just 'Get Info' on the Logic app icon and untick the 'Open in 32bit' tick box.

I have gotten 9.1.8 working under 10.10.x quite successfully but stopped in my experiments there. But Logic 9.1.8 can be booted in 64 bit mode.

You can switch at will. If you have any 3rd party 32-bit only plugs Logic will attempt to load them in bridged mode. Other than that, if you have an issue with a project you can just switch it back to 32 bit mode with no harm done.

The bridge mode is a helper app (located in /Applications/Logic Pro.app/Contents/Frameworks/MAAudioUnitSupport.framework/Versions/A/32-Bit Audio Unit Bridge.app) that will automatically launch if you activate a 32-bit AU plugin when Logic 9 runs in the 64-bit mode.

I'm seeing it often while mastering, because the old TT Dynamic Range Meter is 32-bit only.

Occasionally the 32-Bit Audio Unit Bridge.app may crash (and relaunch) but the rest of Logic usually remains unaffected. At least I haven't noticed any serious issues whatsover, but TT DRM is also the only 32-bit plugin I'm using regularly. Nonetheless it is always a Good Idea™ to relaunch Logic too, if the helper app crashes.

Hi

Whilst I generally use LPX, LP9.1.8 64bit runs fine on OS X 10.11.6 here ( as does LP9.1.8 32 bit).

Make sure to turn off iCloud Drive

CCT