Further on this, I've now put a CD into my Mac and imported the contents into iTunes.
I tried playing it, but the speakers are in the living room and I'm eating breakfast in the kitchen, so I brought the Mac into the kitchen and set it to play through the computer's own internal speakers.
While it plays loudly enough on the speakers, I can scarcely hear it on the internal speakers.
I tried going to Get Info on the file and upping the volume choice, but it didn't make any discernible difference. Hmmm.