CMB File

What are CMB files and how to open them

Are you having problems opening a CMB file or are you simply curious about its contents? We're here to explain the properties of these files and provide you with software that can open or handle your CMB files.

What is a CMB file?

A .CMB file is a Reason Combinator Instrument Patch file.

Reason's Combinator Instrument Patch format is a patch file used by Reason, a music production application by Reason Studios (formerly Propellerhead). It represents complex instrument presets built by combining multiple instruments or effects into a single unit called a Combinator device. It stores all of the devices used in that setup, the way they are connected (audio and control signal paths), the parameter settings for each device, and the Combinator's own settings such as key zones, velocity splits, knob and button mappings, and front-panel customization.

This format is generated by Reason when saving a Combinator patch, or when exporting an Insert FX patch via the "Export Insert FX Patch" dialog. A saved patch can be loaded into Reason's patch browser and dragged or double-clicked to create a Combinator device in the rack with the stored devices and settings automatically recalled. Effect-or Instrument-type Combinators are distinguished by whether they produce sound or process input, and may be used either as instruments or as effect chains.

Files in this format begin with the ASCII signature "FORM" at offset 0, followed by "PTCHCAT" at offset 8, then "REFS" at offset 20. Inside the file are strings such as INIT PATCH, DEVLFORM, and PARM identifying sections related to initial patch state, device form data, and parameter values.

How to open CMB files

Important: Different programs may use files with the CMB file extension for different purposes, so unless you are sure which format your CMB file is, you may need to try a few different programs.

While we have not verified the apps ourselves yet, our users have suggested eight different CMB openers which you will find listed below.

Last updated: August 31, 2026

Various apps that use files with this extension

These apps are known to open certain types of CMB files. Remember, different programs may use CMB files for different purposes, so you may need to try out a few of them to be able to open your specific file.

Help us help others

File.org helps thousands of users every day, and we would love to hear from you if you have additional information about CMB file formats, example files, or compatible programs. Please use the links below or email us at submit@file.org to discuss further.