AAC or AC3

[JosephTocco]

What audio format to use: AAC or AC3? I see in professional use an AC3 (for example on BD). Is it better than AAC?

[Cornucopia]

To use: where? when? Both AC3 and AAC are commercial formats (licensed from Dolby & MPEG, respectively). BD & DVD use AC3 but not AAC, not necessarily for differences in quality but more due to the corporate politics & marketing at the time. Broadcast has used AC3, newer forms would probably use both.

AAC is usually quite more efficient than AC3, mainly because AC3 uses older tech. Quality will depend on bitrate, but I would say that AC3 at 256kbps is roughly equal to AAC at 128 or 96kbps. YMMV.


Scott

[JosephTocco]

To use: where? when?

Sorry, I forgot, in movies. In both, compressed from raw footage or ripped from discs?

[Cornucopia]

Ripped? Go with how it was. Why change it? It should have already been compatible with most things as designed.

In general, let yourself be guided by the target audience & target device/platform. If e.g. you are doing HTPCs, you can use many many formats to choose from. If instead e.g. you are using the built-in player in a TV, it will be the limiting factor as to what is compatible.


Scott

[JoeS99]

I question why AAC is used so widely on downloaded files. I have an old Denon receiver, before HDMI ((I use optical) , and it doesn't play AAC 5.1 correctly, plays as 2 channel. My media players are connected via optical to the receiver. I haven't done my homework on this but do the new receivers process AAC 5.1 thru the optical or only thru HDMI?

[Cornucopia]

Why so widely used? Because it is very efficient (compared even to mp3, ac3).

I have similar Denon receiver. It's not surprising - optical only supports up to 2 channels (or matrixed surround like ProLogic, or special compressed discreet multichannel bitstreams that are masquerading as 2ch within the 2ch structure).
Most receivers from any era prior to HDMI-centric seem to support standard AC3 or DTS 5.1 via optical, and that's it.
You would have to check models to see if a new receiver says it supports aac 5.1 specifically, but if it does, it still might not necessarily support it via optical, as there doesn't seem to be a compressed bitstream standard for that like there is with ac3 or dts. But YMMV so do trial & error testing.
For HDMI, it makes much more sense anyway to decode to uncompressed prior to sending down the pipeline.


Scott

[stonesfan187]

Yes AAC is used because it produces smaller files vs AC3. But I don't think AAC is supported by most home theater equipment where formats like AC3, DTS and PCM are. I would say use AC3 5.1 @ 640kbps which is very good quality.

[jagabo]

I question why AAC is used so widely on downloaded files.

Because that's what Apple uses. And for many years they didn't support AC3 in MP4.