Tokøta (Mastering.com) shows how to build a custom Alchemy instrument in Logic Pro using your own recorded audio instead of Alchemy's built-in sources.
After initializing a blank preset, he imports a sample and it automatically maps across the keyboard. For a more realistic instrument, importing multiple pitches lets Alchemy map them more accurately, though here the goal is just a usable layer, not realism.
Imported samples often cut off instead of sustaining. The fix is entering Edit mode, setting loop points, and switching to Loop mode: continuous keeps the sound going, while forward-backward creates a more textured, evolving loop.
A second sample gets layered in the same way, with tune, pan, volume, and coarse pitch used to shape each layer before combining them into a fuller custom sound.