Update: Currently, as of April 4th 2015, the combination of Logic Pro 9 and Yosemite (10.10.x) is NOT recommended as many people are reporting performance/stability related issues. so long as any external hardware drivers are compatible with 10.10.3 However, as Yosemite seems to make more demands on hardware, there is likely to be quite a noticeable performance hit using LPX and Mavericks/Yosemite compared to the LP9 and Snow Leopard combination Logic Pro X 10.1.1 and Yosemite 10.10.3 seems to be relatively stable. Previous recommendations for Logic Pro 9 users to stay with earlier OS X versions (Preferably 10.6.8 for best performance) still apply for more optimal performance. Ensure any hardware drivers used are fully compatible with 10.10.3 before upgrading to Yosemite. but that's because Yosemite adds/makes a much high demand on system resources For others however, the combo of Yosemite and LP9 is still proving to be unstable so bear this in mind. Update: 20th May 2015: Logic Pro 9 working okay for some users under Yosemite 10.10.3. Do not upgrade unless you have made full 'clone' backups using something like SuperDuper! or Carbon Copy Cloner beforehand, of your current system disk so you can easily roll back if things no longer function correctly after upgrading OS X. Bear in mind most issues relating to Logic after major OS X Upgrades are usually caused by incompatible drivers for external devices or 'broken' 3rd party plugins. I (and hopefully others.) will be testing and publishing results and further information on compatibility here, after 10.11 is out of Beta. Update: July 26th 2015: Reference El Capitan / OS X 10.11.

Note: What follows is a series of personal opinions and advice based on my own experiences and those I have gleaned from other, long time, users of Logic Pro.

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