Bad Sound Input from USB Interface

Hello all,

My school has a news journalism class and we are having some audio issues. We have all the audio entered through a mixer (mics and packages), which goes through XLR to the switcher, from the switcher, it enters a web presenter (SDI audio/video to USB), and from the USB, it enters the Mac which goes straight to YouTube via Webcam. Whenever we play a video with some bass in it, the output volume gets a lot quieter. Being a sound engineer, I know it has something to do with the compression, but unsure if it's the Mac or YouTube compressing it, if it's Mac, is there a way we can disable it? The mixer we use has a built-in USB audio interface and have tried connecting it, but I get the same results so it's not the Mixer or Switcher. I have put headphones on from the phone's port on the mixer and the switcher and it sounds very clean, no compression is on for anything. I'm worried I might have to put a low-cut filter when exporting the news stories from Premier Pro.

TYIA!