Mono Audio: When you’re using headphones, you may miss some audio if you’re hard of hearing or deaf in one ear. That’s because stereo recordings usually have distinct left- and right-channel audio tracks. iOS can help by playing both audio channels in both ears, and letting you adjust the balance for greater volume in either ear, so you won’t miss a single note of a concerto or word of an audiobook.
You can adjust the audio volume balance between the left and right channels. You can use Mono Audio to combine the left and right channels into a mono signal played on both channels. This way you can hear everything with either ear, or through both ears with one channel set louder.
In order to use mono audio:
- Go to Settings > General > Accessibility.
- To combine the left and right channels, turn on Mono Audio.
Source: https://www.razmobility.com/ios-built-in-accessibility/#learn-more