Okay gang, if you have arrived here and have NOT read the last three blogs on playing direct and in-ear monitoring, do it now!
Okay with that out of the way, let's get right down to it, quick-n-simple!
When you can, use a wired, NOT wireless pack!
Why on earth would you drag a CABLE around you might ask, and that's simple: they ALWAYS sound better. Period. Even the cheapest Shure wired packs sound friggin excellent. So if you are a drummer, keyboard player, or any player who basically stays in the same area, go with the wire, you'll thank me later.
When ya gotta go wireless:
Do not, I repeat, do NOT go cheap! Airspace is getting very, very crowded these days, and nobody really cares about our little wireless musical gear, so we are stuck in ever shrinking bandwidth. Manufacturers all do SOMETHING to try to get around this, but it's not easy and requires a ton of engineering and detailed component selection. Almost all packs are digital these days, so think about what happens to the audio/music that's fed to your wireless in-ear pack inside the TRANSMITTER:
The signal is sent through a bandpass filter that makes sure the ultra-highs and ultra lows are cut out, because the digital converter and transmitter can't handle them.
The signal is sent through a brick-wall limiter that keeps the pack from overloading and totally crapping out.
The signal is converted into digital, most likely with a proprietary format.
The ones and zeros are coded do they ONLY are sent to the right pack.
The new coded ones and zeros are sent to a transmitter set to a specific RF carrier frequency,
And then on the pack itself, all that same crap basically happens again in reverse to turn it back into something kinda similar to the audio that was fed into the transmitter!
Are ya all with me?
If ANY of those components/processes along the way are poor, the system will sound like dog poop. If many or all of those components/processes are poor, then you have as nightmare!
So, my hard-n-fast rule to you is this: Go pro. Don't skimp here. Even the LEAST expensive Shure and Sennheiser systems sound perfectly fine and they are not terribly expensive either.
One last tip/words of caution:
No matter what mixer/app you are using to feed the mix to your wireless pack, for God's sake keep the master level well below zero db on peaks. Remember those brick-wall limiters I spoke of earlier? Yep, you feed it to hot and those limiters will kick in and smash/destroy your sound. Trust me, it ain't good.