Signal Processing Toolbox is an additional cost add-on, except for the Student Suite bundle (it is included in the bundle.)
On the main command interface, you can use Add-Ons -> Get Add-Ons, and use the Add-On Explorer to find the Signal Processing Toolbox. If you already have a license for it, it will permit you to install the software; if you do not already have a license, I seem to remember that it offers to take you to the purchase interface.
