Room EQ Wizard (REW) for Beginners: Measure Your Room Free

What is Room EQ Wizard and what does it show you?

Room EQ Wizard is a free acoustic measurement program that plays a test sweep through your speakers, records it with a microphone, and shows what your room did to the sound. The developer describes it as a tool to optimize room acoustics, find the best positions for speakers and listening seat, and configure EQ for room problems^[1]. Builds are available for Windows, macOS and Linux.

For a producer, REW answers questions your ears cannot. Is that boomy 808 note your mix or your room? Did the new bass trap do anything? Does moving the desk 20 cm forward help? Ears adapt to a room within minutes. A saved measurement does not, which makes REW the honest judge of every change you make in the studio.

What equipment do you need to use REW?

You need a calibrated measurement microphone, a way to play the sweep through your monitors, and a stand to hold the mic still. The REW site calls a calibrated USB mic plus your computer's headphone or HDMI output the simplest setup for most measurements, and recommends miniDSP's UMIK-1^[1].

A vocal mic like an SM58 will not do. Measurement mics are small omnidirectional capsules sold with an individual calibration file that corrects their response. Without that file, the graph mixes up the mic's coloration with the room's.

The REW site notes that an analog mic such as the EMM-6 needs an interface with a mic preamp and phantom power^[1]. If you are still choosing an interface, our home studio connection guide covers routing. Add a cheap mic stand or camera tripod. REW's help warns that small mic movements cause large variations, so a fixed support is essential for repeatable results^[2].

How do you set up REW and the mic calibration file?

Install REW, select your mic as the input and your speakers' output device as the output, then load the mic's calibration file. The file is unique to each mic's serial number, so download it from the maker using the number printed on the mic.

Most measurement mics ship with two files. REW's help explains the difference: use a 90 degree calibration file when the mic points straight up, which suits low-frequency work, and a 0 degree file when the mic points at the speaker for full-range measurements. Either way, the mic goes at ear height in your usual listening position^[2].

1. Download and install REW
   Get it from roomeqwizard.com. On macOS, grant REW microphone access in Privacy settings when asked.
2. Download the calibration files
   Enter your mic's serial number on the maker's site and save both the 0 degree and 90 degree files.
3. Set input and output
   Open Preferences, choose the measurement mic as input and the device feeding your monitors as output. Match sample rates on both, for example 48 kHz.
4. Load the cal file
   In the Cal Files tab, assign the 90 degree file if the mic points at the ceiling, or the 0 degree file if it points at the speaker.
5. Position the mic
   Mount it on a stand exactly where your head sits when you mix, capsule at ear height. Mark the spot with tape so later measurements match.

How do you run your first REW measurement?

Set a safe playback level of about 75 dB SPL at the mic, then press Measure and run a sweep from 20 Hz to 20 kHz on one speaker at a time. REW's help says measurements are usually made at around 75 dB SPL, which is not very loud, and warns that loud test signals can damage speakers and ears^[3].

In the Measure dialog, the default sweep level is -12 dBFS and the default length of 256k samples works well for most purposes^[4]. The Check Levels button plays a few seconds of pink noise and warns you if the input is too hot or too quiet. If it is too quiet, raise the input gain, not the speaker volume.

1. Set level
   Open the SPL meter and signal generator, play pink noise, and raise monitor volume until the meter reads about 75 dB.
2. Open Measure
   Press Measure (Ctrl+M), set Start Freq to 20 Hz and End Freq to 20,000 Hz, and choose the left output channel.
3. Check levels
   Press Check Levels and fix any warning before continuing.
4. Sweep and stay quiet
   Press Start and keep still. Turn off fans or air conditioning for the few seconds the sweep runs.
5. Repeat for the right speaker
   Measure the right channel at the same level, then both together. Name each measurement clearly, such as L baseline.

How do you read an REW frequency response graph?

The frequency response graph shows level on the vertical axis and frequency on the horizontal axis at your mix position. A perfect result would be a flat line. Real rooms show big swings below about 300 Hz and smaller ripples above that.

Apply smoothing before you judge the graph, or the high end looks like noise. REW's Variable smoothing uses 1/48 octave below 100 Hz and widens to 1/6 octave at 1 kHz, and REW recommends it for responses you plan to EQ. Psychoacoustic smoothing gives a plot closer to how you hear the response^[5]. Use Var for diagnosing bass and 1/6 octave for a quick overall read.

How do you read a waterfall plot in REW?

A waterfall shows how long each frequency keeps sounding after the sweep stops. Short, even decay across the bass is good. Long ridges that stick out toward the back of the plot mark resonances that keep ringing, which you hear as boomy, smeared low end.

REW generates the waterfall with a default 100 ms rise time aimed at revealing room resonances^[6]. Set the frequency axis to roughly 20 to 300 Hz so the bass fills the view. Ridges that line up with the peaks on your response graph are room modes. Those are the targets for bass traps, because absorption shortens ringing in a way EQ cannot.

Skip the RT60 graph for bass decisions in a bedroom. REW's help explains that RT60 is typically not meaningful below a few hundred Hz in domestic rooms and suggests the waterfall and spectrogram instead. For small rooms under 50 cubic meters it gives 0.3 seconds as the recommended RT60^[7], which is a useful sanity check for the mids and highs.

What should you fix first after measuring?

Fix placement first, then treatment, then EQ. Moving speakers and your chair costs nothing and changes the bass more than any plugin. Measure after every single change so you know what each one did.

• 1. Seat position Slide the mic forward and back in 10 cm steps. The bass response often changes a lot, and one spot is usually clearly flatter. Avoid the exact middle of the room length.
• 2. Speaker position Adjust the distance to the front wall to move boundary dips out of the kick range. Our monitor placement guide explains the geometry.
• 3. Bass trapping Add thick corner traps and compare waterfalls. Stop when new traps no longer shorten the ridges.
• 4. Reflection panels Treat side-wall and ceiling reflection points to calm comb ripples in the mids.
• 5. EQ last Cut the remaining peaks with REW's EQ tool or correction software. Never try to boost a deep null; the room cancels the extra energy and your speakers just work harder.

If you would rather automate the EQ step, compare the approach in our SoundID Reference review with the Dirac Live room correction breakdown. Both still work best after the physical fixes above.