CI2 File

What are CI2 files and how to open them

Are you having problems opening a CI2 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 CI2 files.

What is a CI2 file?

A .CI2 file is a Common Instrument File Format Type 2 file.

Common Instrument File Format Type 2 is a format for storing how natural sound sources such as musical instruments, singers, or speech radiate sound in every direction (a source's directivity), including how this radiation varies by frequency and by phase. It is part of the Common Instrument Format (CIF), standardized by the CLF Group to enable acoustic modeling, sound system design, or virtual acoustics research. CIF Type-2 (the newer version) adds phase information and uses finer frequency bands than Type-1.

These files are created from measurements of the acoustic radiation around an instrument in anechoic or similar controlled environments. Measured sound pressure levels (and now phase) across many directions and across frequency bands are compiled into a file so simulation or modeling software can compute how the instrument will sound in a hall or room under various orientations and placements. Researchers sharing directivity data, or acoustic modeling tools, typically read these files.

A CI-2 file begins with a fixed byte signature "43BD0A000100000000000000000000000000000076312E30" (ASCII: "C...................v1.0") at offset 0, identifying it as a binary distributable version of CIF Type-2.

How to open CI2 files

Important: Different programs may use files with the CI2 file extension for different purposes, so unless you are sure which format your CI2 file is, you may need to try a few different programs.

We have not yet verified any programs for Windows that work with this specific file format. If you know one, please use the 'Suggest a program' link below. Thanks!

Last updated: August 31, 2026

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