Whilst some stations record and play back dry and tracked audio content much louder than songs (and therefore rely on their audio processing to even out the balance), some radio stations either have light or non-existent processing and need a way to play only some audio louder or quieter in relation to others.
In the Cart Setup Options Screen, you can optionally specify that DPS rides the faders automatically in automation mode to account for this. You can also set other fader ride features, such as the depth by which to duck the music, and the speed of fade-down and fade-back-up-again!
But how does DPS know which audio should implement a fader-ride? And which one should be louder?
The answer lies in careful use of the DPS reserved categories. For example, a DRY or tracked link will cause a fader ride to occur because DPS knows that this kind of audio must be heard above the music. IDs may also ride faders as well, depending on the category of the audio that follows them in automation.