If you own the physical DVD retail version, you need the standalone updater (DL1601).
Apple no longer hosts the standalone 9.1.8 DMG installer publicly. logic pro 9 update 918 download free
If you purchased Logic Pro 9 through the Mac App Store, sign out and sign back into your account, then check the Updates sidebar to see if the 9.1.8 version is available for download. If you own the physical DVD retail version,
Beware of third-party sites offering "free" installers. These are often abandonware or, worse, contain malware. 9.1.8 is officially abandonware; use it only if you have the original installer discs or legacy App Store access. Beware of third-party sites offering "free" installers
Resolved performance slowdowns when using plug-ins with frequent graphic feedback.
(Archival pages and forum posts summarizing the 9.1.8 update and third‑party download sites; public release-note excerpts from Apple-era documentation.)