Just to make sure everyone knows what settings you need for REW and a USB microphone without a loopback timing reference:


In REW Preferences:

Click image for larger version. 

Name:	Screen Shot 2021-02-05 at 11.46.42.png 
Views:	715 
Size:	175.4 KB 
ID:	15243




In the Measurement window:

Click image for larger version. 

Name:	Screen Shot 2021-02-05 at 11.44.29.jpg 
Views:	663 
Size:	129.5 KB 
ID:	15242