Room EQ Wizard (REW) is a free, professional-grade program for measuring what your room does to sound. You connect a calibrated measurement mic, play a test sweep through your monitors, and REW shows you your frequency response, decay times and room modes. This guide walks through using it from a standing start, without drowning you in every menu.
🔧 Free tool: try our EQ Frequency Chart.
Quick answer: install REW, load your mic’s calibration file, set input and output, run a measurement sweep from the mix position, then read the SPL graph, RT60 and waterfall to find your room’s problems.
What you need before opening Room EQ Wizard
- A calibrated measurement mic (commonly the miniDSP UMIK-1) and its calibration file — see what is a measurement microphone.
- Your interface and monitors set up at your usual mix position.
- REW installed (it is free and cross-platform). It uses Java, which it will prompt you to install if needed.
Step 1: Set up audio and load the calibration file
Open REW’s preferences and choose your soundcard input (the measurement mic) and output (your monitors). If you are using a USB measurement mic, select it directly as the input. Then load the calibration file that came with your mic so REW corrects for the capsule’s own response. Skipping this step is the most common reason people get misleading graphs.
Step 2: Position the mic and check levels
Put the mic on a stand at your listening height, where your head normally sits, capsule pointing up at the ceiling (the standard orientation for an omni measurement mic). Open the measurement window and use REW’s Check Levels control: it plays a tone so you can set a sensible volume — loud enough to be well above the room noise floor, not so loud it clips.
Step 3: Run the sweep
Set the sweep range (a full-range sweep is fine to start). Click Start Measuring; REW plays a rising sine sweep and records the result. Keep the room quiet. When it finishes you get a measurement you can name and save. Run it again at a couple of nearby positions so you can tell genuine room behaviour from a single-spot anomaly. For the wider method, see how to measure your room acoustics.
Step 4: Read the graphs
- SPL / frequency response — the main graph. Apply moderate smoothing (around 1/6 or 1/3 octave) so you see trends. Big low-end peaks and deep nulls are usually room modes.
- RT60 — REW’s decay analysis shows how long sound lingers. Compare it to a target for a small room; long, uneven decay means too much reflection. Background in what is RT60.
- Waterfall / spectrogram — shows frequencies that ring on after the signal stops. Long low-frequency tails confirm modal problems and where bass trapping is needed.
How to read your frequency response sensibly
The biggest beginner mistake is over-reacting to the raw, unsmoothed graph. With no smoothing the SPL trace looks like a jagged mess of tiny peaks and dips, and it is tempting to try to flatten every wobble. Most of that fine detail is inaudible and changes if you nudge the mic a few centimetres. Apply 1/6 or 1/3 octave smoothing and look at the broad shape instead: a gentle, fairly even slope that tilts down a little towards the highs is normal and healthy in a small room.
Pay attention to the bottom two or three octaves, because that is where small rooms misbehave most. Look for tall, narrow peaks (a frequency the room boosts) and deep nulls (a frequency that almost disappears). These nulls are often caused by a standing wave cancelling the direct sound. Peaks can often be tamed; the deep nulls usually cannot, because the reflection arrives out of phase. Moving the speakers or your seat is the only real fix for a stubborn null — no amount of EQ will refill it.
Common mistakes that ruin a measurement
- Forgetting the calibration file. Without it, the mic’s own response is baked into your graph and you end up chasing problems that are in the microphone, not the room.
- Measuring at the wrong height or spot. The mic must sit where your ears actually are. A measurement taken on the desk or off to one side tells you nothing useful about what you hear when you mix.
- Setting the sweep level too low. If the sweep is barely above the room noise, REW cannot separate signal from background and the decay graphs become unreliable. Get a clear margin without clipping.
- Trusting a single measurement. One sweep at one point can show a freak null that vanishes 10cm away. Always take several and look for what stays consistent.
- EQ-ing before treating. Reaching for filters first is the classic shortcut, and it papers over peaks while leaving the ringing and nulls untouched.
Step 5: Use it to plan treatment (not just EQ)
REW can generate EQ filters, but treat that as a last layer. Fix the acoustics first: corners and modes with bass trapping, reflections with broadband panels. Re-measure after each change to confirm the improvement. REW can also help you tune room correction settings later — see what is room correction software and our take on acoustic treatment vs room correction. Plan the panels with how to treat a room for mixing.
Work in a sensible order: measure to establish a baseline, move speakers and seat to dodge the worst modes, add bass trapping and broadband panels, then re-measure. Only once the room itself is behaving should you let REW design a few gentle EQ filters to smooth the last remaining peaks. Treating REW as a diagnostic tool first and an EQ generator second is what separates a room that genuinely sounds better from one that just measures flatter on paper.
Frequently asked questions
Is Room EQ Wizard free?
Yes, REW is free to download and use. It is the standard measurement tool for home recordists and many professionals.
Can I use REW without a measurement mic?
Not reliably. REW needs a microphone with a known, flat response to give accurate results. An uncalibrated vocal mic adds its own coloration that corrupts the measurement.
Should I use REW’s EQ filters instead of acoustic panels?
No. Fix the room with treatment first, then consider EQ or room correction for the remaining issues. EQ cannot fix deep modal nulls or shorten reverb time, which only physical treatment addresses.
How long does a measurement take?
The sweep itself lasts only a few seconds, and the whole process — setting levels, running several sweeps and saving them — takes a few minutes once you are familiar with it. Most of your time is spent interpreting the graphs and re-measuring after each change you make to the room.
What smoothing should I use when reading the graph?
Start with 1/6 or 1/3 octave smoothing for the overall frequency response so you judge trends rather than tiny, inaudible spikes. You can switch to lower smoothing when you want to study a specific narrow problem, such as a single room mode, but do not make decisions off the raw, unsmoothed trace.
