#5 Mis-use of Compression
I cannot count the number of times I have walked into a gig as a guest mixer and found that Compressors are adjusted incorrectly.
Very recently I was mixing at my friend's church, and the bass sounded like I was moving the fader up and down on every note the bass player played. I looked at the channel strip, and there was not one but two compressors inserted on the bass, When I disabled the comps, the change was so dramatic the rehearsal stopped, and the worship leader says "well you found the bass, thank goodness."
I rarely use compression. I love the dynamic range. Today's sound system can handle lots of dynamic range. Before digital mixers, it was rare that you would see a compressor inserted on every channel. #1 it was too expensive, #2 it is not needed. But give an inexperienced sound person a digital console, and they will put a comp on every input squeezing the life out of everything.
I use parallel compression on Drums, (explained in another post), I use comp on a vocalist with a huge dynamic range to tame transients.
Many people say your live mix need to sound like a record (CD). I would agree the mix needs to sound that way, but not the Dynamic range.
When I mix bands, and they get soft, I pull the levels back. On big crescendos, I push levels up. I accentuate what the group is doing. Dynamics are more exciting than just loud music. If your show starts loud and stays at the same volume throughout the entire program and ends at the same level, you have mixed a boring show. But if your show has dynamics, your audience WILL enjoy it more.
Use compression sparingly. You will get better results than squashing the life out of everything.