Spectrasonics instruments include an in-depth reference guide that you can access instantly from the plugin's interface.
Here are direct links for the reference guides:
To access the Reference Guide directly from Omnisphere, Keyscape and Trilian, simply select the Reference Guide item in your Utility Menu and it will open in your default web browser.
To access the Reference Guide directly from Stylus RMX, click the Floppy Disk icon in the bottom right, and select Reference Guide:
You can find the Reference Guide for Omnisphere 1 here.
