Darth Venal said:
Yeah, Bingowings is right, I think. The people on Alderaan had to have had some idea they were in peril. After all, Bail Organa was well aware what the Death Star was because of his affiliation with the Rebel Alliance. And he surely would have tried to get his people away.

How about a monitor in the background somewhere inside the Death Star observation room, showing a video of Jimmy Smits' face, him being visibly upset and concerned about the Imperial presence, rambling on in desperation to save his people.

There must be a lot of material that could be used, and what he is actually saying would not be much of an issue. It would only detract from the scene if we heard him. It would make sense for the Imperials to have the sound muted -- they ignore him anyway.

There could also be, like a radar display somewhere, with blips showing ships blasting off from the planet. Seeing that the Death Star II's laser was used to destroy ships, it would only make sense that the gunner's control room would have targeting systems that show ships.