REW Cabling and Connection Basics
This thread is a quick reference that covers the basics of connecting cables and SPL meters (or microphones) to Room EQ Wizard software (a.k.a. REW) in order to take audio measurements of any home theater, stereo system, or studio.
Additional details and the use of Room EQ Wizard software (REW) are available in the REW HELP FILES.
REW Connections Using a USB Microphone such as MiniDSP UMK-1 (recommended combo, simplest connections and most economical)
The easiest setup for capturing measurements is a USB microphone that comes with a calibration file. Such a mic can be used for low frequency or full range measurements. If the cal file also has sensitivity data in a format REW recognizes, it can also act as a calibrated SPL meter. The MiniDSP UMIK-1 is recommended and has calibration data in an REW-friendly format, see www.minidsp.com. This mic can also be purchased from our recommended vendor Cross Spectrum Labs for a bit more, with the added benefit of additional 45 and 90 calibration files that are useful for acoustics measurements.
If you are using a USB microphone your computer's headphone output can generate the test signals REW uses, no soundcard needed and no need for soundcard loopback calibration.
If your computer or laptop has an HDMI output you may be able to use an HDMI connection to your processor to generate the test signals, and you may also be able to select the various channels for output (by default REW's test signal is available on the left and right channels of the stereo pair selected in the Soundcard Preferences). Sometimes the various channels can only be selected if you use an ASIO driver for the HDMI output such as ASIO4All, that requires the latest (beta) version of REW.
REW Connections Using an ECM8000 Microphone and External USB Audio Interface with Integral Microphone Preamp with Phantom Power (recommended combo)
USB audio interfaces that offer an internal preamp with phantom power preclude the use of a separate sound card and mic preamp (as discussed below). This simplifies the connections and offers easier portability of the equipment. TASCAM, M-Audio, Presonus, Focusrite etc. offer such units. However, it is best to keep things simple when choosing an interface. This post indicates that higher-end, complex interfaces do not work well with REW.
Typically these audio interfaces exhibit flat frequency response and as such do not need a soundcard calibration performed. However, a loopback may be desirable for an acoustical timing reference. To accomplish a soundcard calibration, a loopback cable is connected from a channel line-out to a channel line-in and then removed once the calibration file is created and saved. It is not necessary to perform the calibration utilizing the microphone input. Experience has shown that the mic stage response anomalies are small and that response drop-off is mainly attributed to the line stages.