l3codecp.acm

Audio codec module

An .acm file is an audio codec for the Audio Compression Manager on Windows. The file is a DLL in the PE format. The system loads it to compress and decompress audio streams, for example with the GSM or ADPCM codecs. Windows ships several such codecs, for example msg711.acm. Modern applications use Media Foundation in its place.

A file extension is only a part of the file name. It does not give a guarantee about the format or the content of a file. But on Windows, the extension selects the program that opens the file.