well, modems were originally in the audible range as they went over phone lines and saving to cassette was one of the earliest consumer media (which was a shrunken-head version of the reel-to-reel from the 60s computers) – and that was also audible range.
So the I/O in the audible range was usually incorporated either through cassette reading/writing and/or modem sending/receiving as they were almost identical.
This is ROM – Read Only Memory because the capacity to write to it wasn’t there. There were a number of fascinating experiments in transferring data when modems and saving mechanisms were audible-ranged.
oh, so aux-input.