[Wayne A. Pflughaupt]

Hmm... The Shure link is the only one I can get to open.

Any measuring will only be as good as your equipment. Since only the most expensive equipment is truly flat, calibrations are needed to compensate for the inadequacies inherent to the relatively inexpensive equipment we use for REW.

The REW software can calibrate itself for any suitable sound card. However, your mic of choice is a problem. Did you look at its frequency response?

Shure specs it at rolling out at 6 dB-octave below 100 Hz, with the rumble filter set flat. IOW, your readings are going to be down more than –12 dB at 20 Hz.

Obviously, no mic is perfect. We have available a calibration file for the common Radio Shack SPL meter most of us use. I understand it’s possible to create a mic calibration file for REW, if you know the response characteristics of the mic. It would be a bit “iffy” to do that given the rather coarse resolution the Shure graph uses, but it’s possible you could create a calibration file for the SM-81. Other members here more familiar with what that entails can tell you how.

As noted, I couldn’t open the link for the USB interface. The soundcard you use has to be full duplex; if your interface has that capability, you can use it. The REW Help Files can show you how to calibrate it.

Regards,
Wayne