What Is REW?
Room EQ Wizard (REW) is a free, cross-platform application for measuring and analysing room acoustics. It generates test signals, captures them through a measurement microphone, and produces frequency response plots, waterfall plots, RT60 calculations, impulse responses, and more.
REW is the de-facto standard tool in home studio acoustics. It is available for Windows, macOS, and Linux at roomeqwizard.com.
Equipment Needed
- Measurement microphone — an omnidirectional condenser mic with a known (or calibratable) frequency response. The UMIK-1 from miniDSP is the most popular budget option; it connects via USB and comes with a calibration file.
- Audio interface — if you use a standard measurement mic (e.g., Behringer ECM8000, Dayton EMM-6), you need a USB audio interface with phantom power (+48V). If you use a UMIK-1, the interface is built in.
- Mic stand — position the mic at your ear height in the listening position. A sturdy stand prevents vibration artifacts.
- Your monitors — the speakers you are measuring through. Leave them at your normal listening level.
Measurement Setup
1. Install and Configure REW
Download and install REW. On first launch, go to Preferences > Soundcard and select your audio interface for both input and output. If using a UMIK-1, load the calibration file via Preferences > Mic/Meter.
2. Set Levels
Use REW's SPL Meter to check that the measurement level is in the right range. The test signal should be around 75 – 80 dB SPL at the microphone position. Too quiet and the signal-to-noise ratio suffers; too loud and you risk clipping or disturbing neighbours.
3. Run a Sweep
Click Measure and configure a logarithmic sine sweep. Default settings (256k length) work well for most rooms. Run the sweep once for the left monitor, then once for the right. You can also measure both together for a combined response.
4. Repeat at Multiple Positions
A single measurement only tells you about one point in space. Measure at your primary listening position, then move the mic 15 – 20 cm in each direction (forming a small grid) to see how the response varies. This reveals whether bass problems are positional (modes) or structural.
Reading the Results
Frequency Response
The primary plot. A flat line would mean perfect reproduction. In reality you will see peaks (room modes, boundary reinforcement) and dips (cancellations, SBIR). Apply 1/3-octave smoothing for a clearer picture of the overall trend.
Waterfall Plot
A 3D plot showing how sound decays over time at each frequency. Room modes appear as ridges that persist long after other frequencies have died away. These ridges indicate frequencies that will sound boomy and smeared.
Look for ridges that extend beyond 300 ms — these are the modes that need treatment. A well-treated room shows a waterfall that decays uniformly across all frequencies.
RT60
REW calculates RT60 from the impulse response (using T20 or T30 extrapolation). Check octave-band values from 63 Hz to 8 kHz. Typical studio targets are 0.2 – 0.4 seconds across all bands.
Energy-Time Curve (ETC)
Shows individual reflection arrivals over time. The direct sound arrives first (the tallest spike), followed by reflections. Large spikes within the first 20 ms indicate strong first reflections that should be treated.
Using REW with SAMESOUND Tools
SAMESOUND calculators let you predict room behaviour before measuring. REW lets you verify those predictions. A powerful workflow:
- Use the Room Modes calculator to predict modal frequencies, then check against REW's frequency response to confirm which modes are actually problematic.
- Use the RT60 calculator to estimate reverberation time with planned treatment, then measure with REW after installation to verify.
- Use the Room Analyzer tool to input REW measurements and get actionable treatment recommendations.
Prediction and measurement together give you a complete picture: the calculator tells you why a problem exists; the measurement tells you how severe it is.