CI1 File

What are CI1 files and how to open them

Are you having problems opening a CI1 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 CI1 files.

What is a CI1 file?

A .CI1 file is a Common Instrument File Format Type 1 file.

Common Instrument File Format Type 1 is a version-1 file format of the Common Instrument Format (CIF) standard. It stores how sound is emitted from natural sources (like musical instruments, singers, or environmental noise) in all directions, for different frequency bands. It is used when the angular or spatial behaviour ("directivity") of an instrument or natural sound source needs to be measured, preserved, shared, or used in simulations of acoustic spaces. Version 1 captures magnitude data only; later version 2 adds phase information. Sources belonging to its development include the CLF-group.

Files in this format are produced by measurement or modelling systems that characterize natural sound sources for directivity, such as acoustic researchers or audio software focussing on realistic modelling of sound propagation. After collection of directivity data, these files are often consumed by room-acoustics simulators, virtual instrument renderers, or other audio tools that require spatial emission patterns of sources rather than simple point-source assumptions. Distribution and archival of these directivity datasets also utilise this format because version 1 is compact (only magnitudes) and simpler than version 2.

Version identifier and file signature details appear from the binary value at the start of the file: the first bytes are "42 BD 0A 00 01 00 … 76 31 2E 30", representing, in ASCII terms, a header string ending in "v1.0". That signature is found at offset zero of the file.

How to open CI1 files

Important: Different programs may use files with the CI1 file extension for different purposes, so unless you are sure which format your CI1 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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