Association

• According to the file extension database FILExt, there is no information on files with the .ef extension. The extension may be typed incorrectly or the file that you possess is invalid.
  
  

Ensoniq

• Ensoniq offers a line of music software that enables users to emulate different musical instruments. These files all begin with ".ef," with a third letter representing a unique instrument or synthesizer.
  
  

Troubleshooting

• If you encounter a file with the extension .ef it is important to make sure that you know where it came from before attempting to open it. Since the extension is not valid, it is possible the file could pose security threats to your computer. Additionally, .ef files may be incorrectly named by another user and may function if the extension is altered. If someone were to give you an .ef file, you should ask him what function the file offers to better judge what to rename it.