Well my electrical engineering degree is severly dated, but as I remember, the carrier wave carries the information about the code. While there are several methods that can be used, a modulated carrier is the most common. We have a basic sine wave (carrier wave with it's own frequency) and this is modulated (kind of combined with a second wavform) to produce a signal that has pulses (bursts). This pattern contains the IR information.

Pronto has the capability of learning this information up 56kHz in frequency (carrier wave). There are few devices (very few) that use frequencies above this. If the manufacturer will give you the carrier frequency, and it's below 56kHz, you are almost guaranteed success.

Look here: [Link: geocities.com], Figure 1 and 2 about half way down the page.