text: module in control panel named ac3 -- what is this for? i have windows 98 with updates.  cannot pull up properties on this module, never noticed it previously, is this normal part of software? ac3 is normally a audio codec, primarily used in video files to encode the audio.   a direct quote from pcmag:  definition of: ac-3   (active coding-3) dolby's third digital audio coding technology based on a perceptual coding method. it is more advanced than ac-2 and provides six channels of audio in less space than two-channel stereo cd. ac-3 and "dolby digital" are synonymous. see dolby digital.   the control panel object should be a graphical front end to which ever ac3-decoder or encoder codec that's installed on your computer.  this control panel object should allow you to change various options associated with how ac3 works.  divx is a popular video compression that can utilize ac3 sound streams.  there are many other popular products that either use the ac3 decoder, or possibly even allow you to encode your sound files into the ac3 standard.  creative labs has such products.  the control panel object normally shows up when you install a product that uses one of the open-source ac3 decoders.  there may be commericial software that will install this object as well, of course.  hope this helps a little.