What is a AC3 file?
AC3 — Dolby Digital
What is it?
AC3, better known as Dolby Digital, is the format behind multichannel sound: five speakers plus a subwoofer, the famous 5.1 setup.
It's the soundtrack format on nearly every DVD, Blu-ray disc, and digital television broadcast. Each channel is encoded separately, which lets sound move around the listener rather than simply coming from the front.
History & origin
Dolby developed AC3 in the early 1990s for cinema use. It first appeared in theaters in 1992, before going on to become the standard audio format for DVD.
It has outlasted every generation of media that followed and remains, thirty years on, the reference format for home theater sound.
Why it is useful
Multichannel sound with universal compatibility: every home theater receiver can decode it.
A reasonable bitrate given what it delivers.
Limits & drawbacks
Its compression scheme shows its age: newer formats do better at the same bitrate.
A standalone AC3 file won't play on a phone or computer without conversion — and without a multichannel setup, it loses much of its point.
Practical tips
To play an AC3 track on an ordinary device, convert it to MP3 or AAC: the sound will be downmixed to stereo, which is exactly what you want for headphones.
Keep the original AC3 file if you have a home theater setup: that's the one place where it truly makes sense.
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