Before we start on this white noise machine review, we need to review what white noise is in association to these sound machines we've tested. “White noise machines” and “sound machines” are used pretty interchangeably, but you need to actually dig into the details to know what you're actually hearing. If you've seen pink noise, brown noise, and green noise amid all the white noise machine chatter, it's because more often than not, you'll find those options available to you wrapped up into one little machine.