How do I export an MDAT file from REW?

In REW, go to File → Save All Measurements or File → Save Measurement. Choose a location and save the file with the .mdat extension. You can also use File → Export → Export All Measurements As MDAT.

What information does an MDAT file contain?

An MDAT file can contain frequency response measurements, waterfall data, phase information, impulse response data, RT60 measurements, measurement notes, and project settings such as calibration data and graph preferences.

Why do forums ask for MDAT files instead of screenshots?

Because MDAT files contain significantly more information than a screenshot. They preserve the underlying measurement data, allowing others to analyse the results in detail, change graph settings, overlay measurements, and make more accurate diagnoses.

Can AudioBro analyse my MDAT file?

Yes. AudioBro can process MDAT files as part of room analysis. Upload your MDAT file and AudioBro will interpret the measurement data, identify key issues, and provide prioritised recommendations.

Should I include all measurements in the MDAT file?

Yes, including all relevant measurements provides the most complete picture of your room. Multiple measurements from different positions help identify whether issues are localised or consistent throughout the listening area.

Getting Started

•June 20, 2026•8 min read

What Is An MDAT File? The REW Measurement Format Explained

Q: What is an MDAT file?

An MDAT file is the native project format used by Room EQ Wizard (REW). It stores measurement data, graphs, phase information, timing information, and project settings inside a single file.

Q: Can I open an MDAT file without REW?

MDAT is a proprietary format designed for REW. While the file is based on a structured data format, REW is the primary tool for viewing and working with MDAT files. AudioBro can also process MDAT files as part of room analysis.

AudioBro

What Is An MDAT File? The REW Measurement Format Explained

If You Use REW, You Need To Understand MDAT Files

If you have spent any time in audio forums asking for help with room measurements, you have probably been asked to upload your MDAT file.

For many beginners, this request is confusing.

You already posted a screenshot of your graph. Surely that is enough?

Usually it is not.

Understanding what an MDAT file is, what it contains, and why it matters is one of the most practical things you can learn as someone who measures their room.

This article explains everything you need to know.

This article is part of our comprehensive REW guide: REW Shows You The Problem. AudioBro Explains What To Do About It..

What Exactly Is An MDAT File?

MDAT is the native file format used by Room EQ Wizard (REW).

When you save your work in REW, it creates an MDAT file. The extension stands for Measurement Data.

Think of it as the complete project file for your measurement session.

Instead of saving just a picture of a graph, the MDAT file stores the underlying measurement data itself.

This means anyone who opens the file can:

View the original measurements
Change graph settings and smoothing
Overlay multiple measurements
Analyse phase, waterfall, and impulse response data
Read measurement notes
Re-process the data with different parameters

A screenshot only captures one specific view at one specific moment.

An MDAT file captures the evidence behind the view.

What An MDAT File Contains

A single MDAT file can contain a remarkable amount of information.

Frequency Response Data

The most common content. Each measurement captures the full frequency response at the measurement position, including level information across the audible spectrum.

Waterfall Data

Waterfall plots showing how sound energy decays over time are stored alongside frequency response data. This allows anyone reviewing the file to assess bass ringing and decay characteristics.

Phase Information

Phase response data is preserved, which is essential for diagnosing integration problems between speakers and subwoofers.

Impulse Response Data

The raw impulse response that underpins many other measurements is stored in the file. Advanced users can re-process this data to generate additional analyses.

RT60 Measurements

Reverberation time data may be included if RT60 measurements were captured during the session.

Measurement Notes

Any notes you added to measurements within REW are preserved. This is valuable for documenting measurement conditions, microphone positions, and other contextual information.

Project Settings

Calibration data, graph preferences, window settings, and other configuration information is stored in the file.

Split screen comparing a simple screenshot vs complete MDAT measurement project

Why Screenshots Are Not Enough

This is the key point that many beginners miss.

Imagine two systems that both show a large dip at 80Hz on a frequency response graph.

The screenshots may look identical.

The causes may be completely different.

One system might be suffering from a room mode cancellation.

The other might be dealing with an SBIR null caused by speaker placement near a boundary.

The solution for each problem is different.

Room modes might require repositioning the subwoofer or adding a second one.

SBIR might require moving the speaker relative to the wall.

These are fundamentally different fixes for what looks like the same problem.

An MDAT file allows an experienced reviewer to:

Examine the waterfall plot for ringing that indicates a room mode
Check the phase response for integration issues
Compare multiple measurements from different positions
Assess whether the dip is consistent or position-dependent
Review the impulse response for timing clues

None of this is possible from a screenshot alone.

This is why experienced users almost always request the MDAT rather than the screenshot.

How To Save An MDAT File In REW

Saving an MDAT file in REW is straightforward.

Save All Measurements

Go to File → Save All Measurements.

This saves every measurement in your current session into a single MDAT file. This is usually the best option when sharing with others or uploading for analysis.

Save A Single Measurement

Go to File → Save Measurement.

This saves only the currently selected measurement. Use this if you want to share a specific measurement without including all the others.

Export Options

REW also provides export options under File → Export for saving data in other formats. However, the MDAT format preserves the most information and is the preferred format for sharing.

Best Practices For MDAT Files

Include Multiple Measurements

A single measurement rarely tells the complete story. When saving an MDAT file for analysis or sharing, include measurements from multiple positions if you have them.

This provides a more representative picture of room behaviour.

Add Notes

REW allows you to add notes to individual measurements. Use this feature to document:

Microphone position
Speaker configuration
Subwoofer settings
Crossover frequency
Any changes made between measurements

These notes are invaluable for anyone reviewing the data later, including yourself.

Use Meaningful Filenames

Instead of saving files as "measurement1.mdat" or "untitled.mdat", use descriptive names such as:

"living-room-left-seat-2024-01-15.mdat"
"basement-5.1.4-all-measurements.mdat"

This helps you and others identify the file later.

Save After Each Session

Make it a habit to save your MDAT file after each measurement session. REW does not auto-save, so if the application closes unexpectedly, your measurements may be lost.

Keep Original Files

If you make changes to measurements within REW, consider saving the original unmodified file as well. This preserves the raw data for future reference.

Acoustic measurement data transforming into clear room recommendations

How AudioBro Uses MDAT Files

AudioBro can process MDAT files as part of its room analysis workflow.

When you upload an MDAT file, AudioBro:

Extracts the measurement data
Identifies key issues such as room modes, SBIR, and phase problems
Prioritises the issues based on audible impact
Provides specific, actionable recommendations
Explains what each measurement means in plain language

This addresses the most common challenge that REW users face: understanding what their measurements actually mean and deciding what to fix first.

REW gives you the data. AudioBro helps you interpret it. For a detailed look at how these tools complement each other, see Room EQ Wizard vs AudioBro: Measurement vs Interpretation.

Common Questions About MDAT Files

Can I Open An MDAT File Without REW?

MDAT is a proprietary format designed for REW. While the underlying structure is accessible, REW is the primary tool for viewing and working with MDAT files.

AudioBro can also process MDAT files as part of room analysis.

How Large Are MDAT Files?

MDAT files are typically small, usually between 50KB and 2MB depending on the number of measurements and the amount of data captured. They are easy to share via email or forum attachments.

Is An MDAT File The Same As A Calibration File?

No. A calibration file (such as a UMIK-1 calibration file) contains microphone sensitivity data used to ensure accurate measurements. An MDAT file contains the measurement results themselves.

These are different files serving different purposes.

Can I Edit An MDAT File?

You can modify measurements within REW after loading an MDAT file, such as applying smoothing or adjusting graph settings. However, the raw measurement data itself should not be edited outside of REW as this could compromise data integrity.

What If My MDAT File Will Not Open?

If an MDAT file will not open in REW, it may have been created with a different version of REW. Try updating to the latest version. If the file is corrupted, there may be no way to recover the data, which is another reason to maintain backups.

Why Understanding MDAT Files Matters

If you are using REW to measure your room, understanding the MDAT format is not optional.

It is the mechanism by which you:

Preserve your measurement data
Share data with others for diagnosis
Maintain records of your room's behaviour over time
Enable tools like AudioBro to analyse your measurements

A screenshot is a snapshot.

An MDAT file is the complete picture.

The next time someone asks for your MDAT file on a forum, you will understand exactly why they are asking.

And more importantly, you will be able to provide it confidently, knowing that the file contains everything needed for an accurate and thorough analysis.