AEGIS Is a form of Digital Encryption for EDACS systems. It is the oldest of the Digital formats that GE-Ericcson, now M/A-Com had. It is on the way out in favor of thier Provoice format. It is not scrambling/inversion, it is true encryption. When used on a TG, you can not hear anything but a electronic buzz/warble. A lot of people mistakenly think that AEGIS is like Provoice in that you cant hear any TG's.... with PV, you can set up the system to be pure digital, or mixed mode with some analog TG's. PV digital TG's are always digital and can't be heard on any scanner made. With AEGIS, you can turn it on and off on ANY TG. When enabled, you can't hear the traffic on the TG, but when its switched off, you can hear the coms clearly. AEGIS is used rarely on the Shelby County EDACS TRS. Years ago it was used a lot more. As for the Memphis City TRS, it uses the oldest Motorola Digital Format= ASTRO VSELP. It is an unmonitorable digital format, and is also on the way out as its being replaced with the ASTRO (3.6 KBPS IMBE), and the ASTRO-25 (9.6 KBPS IMBE "true P-25").