I recently came across a video online that had all the audio on the left channel. It was a recording of a talk, and having the speaker’s voice coming out of only the left speaker was very distracting.
Thankfully, there’s a quick way to fix this. Macs and recent versions of Windows have an accessibility feature that combines stereo audio into a single mono channel (which is then distributed equally to both of your speakers).
On a Mac open System Preferences, choose Accessibility, select Audio from the list on the left, then check the Play stereo audio as mono box.
On Windows 10 press Windows Key + U to bring up the Ease of Access Settings, click on Other Options, then turn on the Mono Audio setting.
After enabling this setting, you can concentrate on what matters. Just remember to turn it off when you’re done!