What Is REW (Room EQ Wizard) and How Do You Use It for Room Measurement?

REW (Room EQ Wizard) is free software for measuring and analyzing room acoustics, loudspeakers, subwoofers, and audio devices. You use it to see how your room and system actually behave, then act on that data: find better speaker, subwoofer, and listening positions, and configure EQ to reduce room problems. It is a practical fit if you have a computer, a measurement microphone, and an audio interface or receiver you can connect to. The current version listed on the site is V5.31.3 (25 July 2024).

What REW does

REW covers the full measurement chain rather than just one device:

• Room acoustics: measure the listening room, studio, or home theater and identify resonances and room modes.
• Speaker and subwoofer placement: compare positions using measured response instead of guesswork.
• Device and chain analysis: analyze the performance of the whole audio reproduction chain.
• EQ configuration: use parametric equalizers to tackle room problems the measurements reveal.
• Visual analysis: frequency response, waterfall/spectrogram views, and room mode identification are part of the toolkit.

The site describes these as "free professional-grade tools" aimed at finding "a path to better sound."

The core workflow

1. Prepare the hardware

You need a measurement microphone, a way to get its signal into the computer (audio interface or a receiver/processor with digital input), and a playback path to your speakers or subwoofers. REW's own Equipment page and help files cover supported setups.

2. Install REW

Downloads are organized by OS:

There is also a sample data file (Sampledata.mdat) you can open to explore the interface before measuring your own room. On macOS, you may need to grant REW access to the microphone and to the folders where measurements are saved—especially the desktop—through Privacy settings.

3. Measure

Connect the mic, confirm input levels, and run a measurement sweep. The expected result is an impulse response from which REW derives frequency response and time-domain views. Repeat at each candidate speaker, subwoofer, and listening position you want to compare.

4. Analyze

Read the frequency response for overall balance and obvious peaks and dips, use waterfall/spectrogram views to see how energy decays over time, and identify room modes—the resonances that cause boomy or uneven bass. This is where placement decisions get made: move a subwoofer or seat, re-measure, and compare.

5. Apply EQ

Use REW's EQ tools to design parametric filters targeting the problems you measured, then enter those settings into your equalizer or processor. Re-measure afterward to verify the result rather than assuming the predicted curve matches reality.

Getting help and learning the tool

REW ships with comprehensive help, and the same material is available online, as downloadable HTML for offline use, and as a PDF snapshot (V5.20, September 2021). The site notes the online and in-application help are the most current; PDFs are snapshots. Community support lives at the AV NIRVANA REW forum, which also hosts beta builds. Translations of the V5.20 help exist, including French (Patrick Del Basso, January 2022) and Chinese (Johnson Chow, Initial Audio Concept, October 2021).

Free vs. Pro upgrade

The base software is described as free, with donations invited to support development. The Pro upgrade adds capabilities aimed at more advanced measurement work:

• Simultaneous measurement of multiple inputs with RMS averaging
• Adjustable weighting for each input and level alignment
• Up to 16 input traces on the RTA, in addition to the RMS average
• Speech Transmission Index calculation from the impulse response (indirect method, per IEC 60268-16:2020)

If you are measuring one listening position with a single mic, the free version covers the core workflow. The Pro features matter when you need multi-input capture, averaging across sources, or speech intelligibility metrics.

Common sticking points

• Mic permissions on macOS: blocked mic or folder access is a frequent first-run failure; check Privacy settings.
• Linux dependency: the Linux installer requires a Java 8 runtime.
• Trusting the prediction: EQ filters designed in REW are predictions—verify with a fresh measurement.
• Version drift in help files: use the online or in-app help for current features; the PDF is a 2021 snapshot.

Start with the sample data file to learn the interface, then take one measurement of your current setup before changing anything—that baseline is what every placement and EQ decision gets compared against.