Question

I am using the audio interface usb connection to play sound from my Mac. Everything that plays back is missing frequencies. Certain instruments become non existent. I am almost positive the left sound output is the same for the right. I do have them panned and can control individual left and right.

Answer 1

Please ensure you have setup this correctly. 

Link: https://support.presonus.com/hc/en-us/articles/115001134163-Tape-In-USB-Playback-Routing-on-the-StudioLive-Series-III

If you source is causing the issue then try basic playback like YouTube/iTunes. 

If the issue remains then please log a support ticket. 

Link: https://support.presonus.com/hc/en-us/articles/210050813-How-to-create-a-new-Support-Request-

Answer 2

Can you try an audio signal without computer (USB), just to check if the mixer is ok? Do you have a cable to connect the headphone output of your Mac with Tape In or Aux In on the back of your mixer? Or input channels 1+2 (XLR) or 17+18 (combo)?