AC3Filter is a high quality free audio decoder and processor filter. It allows media players to playback movies with AC3 and DTS audio tracks. Also it can process any audio track, much of processing options allows to adjust the sound in almost any way. It is possible to upmix any audio source to 6 channels. Filter can do multi-channel and digital (SPDIF) output. It can encode any audio source to AC3 on-the-fly and send it over SPDIF to the receiver.

With AC3Filter you can:

Playback:

Watch movies with AC3 and DTS audio tracks
Listen multi-channel (AC3/DTS) AudioCD
Playback WAV files with AC3/DTS content, ripped from multi-channel AudioCD without any conversion of these files.
Playback raw .AC3 and DTS files (with help of AC3File filter)

Process:

Up-mix any audio track (even plain stereo) up to 6 channels
Down-mix any audio track to any number of channels (to match your speaker configuration)
If you have an external Dolby ProLogic decoder, you may use ProLogic down-mix to help DPL decoder to extract surround information
Watch movies under poor hearing conditions (noisy environment, weak speakers, ...)
Decrease dynamic range to watch movies at night
Apply time shift to the audio track to synchronize audio with video.
Adjust gain of every input/output channel independently to compensate loudness differences
Adjust time delays for every channel to compensate different distances to loudspeakers.

SPDIF output:

Passthrough AC3 and DTS over SPDIF without any change to external decoder
Encode any audio to AC3 and transmit it over SPDIF
USB sound cards supported.