One of the things I've had to learn as an audio engineer is how to mix in mono and check stereo mixes for mono capability.
Before I can send off my song to mastering, I need to make sure that I have a good mix that translates sonically to any speaker. This is where mixing in mono is a great help! If it is to sound good even on a cheap pair of earphones or a poor car stereo, I can check to see how it will perform by turning off the stereo and listening in mono (all the sound going up the middle of the room). This pushes all the frequencies into the middle and anything that is lost when mono is on is because there are cancellations between the left and right taking place. (+1 plus -1 =0) These can be fixed in various ways and that's what I am trying to do today.
I've noticed that my mix of the song The Vine sounds almost half as loud when I turn the mono button on in my output channel than it does when it is off. This is a red flag. I believe that it is the synths that aren't doing well in mono so I went through my mix and listened to see what was dropping in volume when I turned the mono button on - it was, indeed, the midi tracks with synths and strings.
I could see this too, in Logic, when I looked at the Multimeter plugin's correlation meter. The pointer was all the way to the left for the most part. Not good. That means the tracks need to panned more evenly.
So I read some articles and watched some YouTube videos about how to fix this and this is what helped me. (see the links below)
What I'd done wrong
One miss I was doing was to only mix with my earphones. That's why this could sneak up on me. It is a good idea to listen from time to time with your speakers and move your head around, walk around in the room and listen for frequency issues. I had just mixed with my earphones on and tricked myself that everything was o.k.
Another thing I was not doing was mixing in mono from the start. It would have shown me that there was a problem there as I went along.
Nowadays I mix in mono as much as possible. The, when I turn on the stereo I get a pleasant boost. But it still sounds good on small speakers.
Links:
Barry Gardner's article from resoundsound.com was extremely helpful:
Maintaining Mono Compatibility In Your Music Mix
http://www.resoundsound.com/mono-compatibility/