The 9520 is a stand-alone, single rack unit, 20 x 10 video switcher. One or more 9520 video switchers can be combined with 9521 audio switchers to provide a maximum of 7 switching levels.
Typical configurations:

One 9520 and one 9521 switcher providing a complete 20 x 10 video and dual audio system in just two rack units
Two 9520 switchers with one 9521 switcher producing a 20 x 20 video and mono audio system in three rack units
Three 9520 switchers and one 9521 switcher forms a 20 x 10 RGB and dual audio system in four rack units
A front mounted control panel and redundant power supply are optionally available

The 9521 is a stand-alone, single rack unit, 20 x 10 dual audio or 20 x 20 mono audio/time code switcher. One or more 9521 audio switchers can be combined with 9520 video switchers to provide a maximum of 7 switching levels.
Typical configurations:

One 9520 and one 9521 switcher providing a complete 20 x 10 video and dual audio system in just two rack units
Two 9520 switchers with one 9521 switcher producing a 20 x 20 video and mono audio system in three rack units
Three 9520 switchers and one 9521 switcher forms a 20 x 10 RGB and dual audio system in four rack units
A front mounted control panel and redundant power supply are optionally available.