From the fifth-generation iPod on, Apple introduced a user-configurable volume limit in response to concerns about hearing loss. Users report that in the sixth-generation iPod, the maximum volume output level is limited to 100 dB in EU markets. Apple previously had to remove iPods from shelves in France for exceeding this legal limit. However, users that have bought a new sixth-generation iPod in late 2013 have reported a new option that allowed them to disable the EU volume limit. It has been said that these new iPods came with an updated software that allowed this change. Older sixth-generation iPods, however, are unable to update to this software version.

What type of sensory issue was a concern prior to the release of 5th gen iPods?