The biggest jump in quality in GarageBand 10.4.8 comes from switching your project’s bit depth. By default, many older projects might be set to 16-bit (CD quality), but for professional-grade audio, you should move to 24-bit.
While previous versions of GarageBand were stable, the fear of losing a project often led to cautious creativity. Version 10.4.8 introduced much-requested stability improvements and, crucially, a more robust handling of plugin validation and third-party Audio Units (AU). This allows producers to integrate high-end third-party plugins (like Native Instruments or Spitfire Audio garageband 1048 high quality