Mono audio is simply 1 channel of audio duplicated to multiple channels. It should sound obvious with headphones because it will usually sound like it’s in the middle of your head.
I like to describe stereo more as how one would hear sound in the real world if you pull your fingers out of your ears. The sound should be wide with music, representing a live environment like a club or stadium, with kick drum and lead vocals in the center and other instruments, reverb and backing vocals off to each side. With movies and TV shows, the dialogue should mostly come from the center while background ambient sounds and cars zooming by will come from both sides depending on where the action is on-screen.
Learn More… Monaural (Mono) & Stereo
This guy struggles to teach the difference... (You can skip the long guitar intro.)
NOTE: In the last 5 of my 15 years multi-media experience, this problem has come up more and more. Even with music videos which should always be stereo! I’m not sure why but I want to make sure we all know what to look for. Keep in mind that just because the metadata of a file reports that the audio is 2 channel stereo doesn’t mean it is stereo. The only thing that data is good for is telling you how many channels of audio it contains. Never, ever should we QC audio on a laptop or tablet through it’s built-in speakers. Always use headphones. I trust my ears but just to be safe, when in doubt, use a scope. I have found a good one bundled with Final Cut Studio, in SoundTrack Pro. Import your video or audio file and in the effects tab on the left choose “Metering”, then “Multimeter” and click the plus icon to pop up the scope. Click the button for “Goniometer” and play several points of your audio timeline. If the scope shows the audio in the vertical-middle then you my friend have mono tracks.
Here are good examples to listen to in stereo and mono.