Watching through TNG, I'm curious, with all the capabilities of Geordi's visor, could it be calibrated to pick up sound waves? There's so many other things that it picks up, that this seems like it would be simple enough.
The VISOR Geordi wears was only capable of scanning the electromagnetic spectrum from 1 Hz to 100,000 THz. As DVK's answer mentions, sounds is a mechanical movement of the air, and not electromagnetic.
Now, could a device similar to Geordi's VISOR in appearance be built that worked via sonar? Definitely. There are primitive (compared to 24th century technology) devices available today, fashioned around sun glasses, that already do that.
I'm not aware of any explicit capability to pick up sound waves (which are mechanical movement of air molecules, unlike electromagnetic waves used for vision).
The closest the topic was discussed was mentioned on Memory Alpha:
While being held hostage on Arkaria Base, the crew of the USS Enterprise-D reconfigured the VISOR to emit a hypersonic pulse to incapacitate their captors. (TNG: "Starship Mine").
Now, this merely indicates that they were able to emit the sound... but generally the same sort of hardware can be used to emit and produce a sound (e.g. piezoelectric stuff) which means that turning the VISOR into a sound recorder would not be much more difficult than into a sound transmitter, even if the capability is not there out of the box.