AU Lab

https://www.apple.com/apple-music/apple-digital-masters/

Apple’s free digital audio mixing application, AU Lab, can be used as a host application for Audio Unit effects, including the AURoundTripAAC plugin, one of the Apple Digital Mastering tools. If you don’t already have Logic or another Audio Unit host application, download AU Lab to get started with auditioning your audio, detecting peaks and clipping, and performing double-blind listening tests.

here is a description of how you can use it to set up an audio monitor