2 channel ac3 & azid

[HotSpur]

I've looked through doom9's ac3 > mp3 guides and searched the audio forum but I can't figure out the proper command line to use azid with a 2 channel ac3. From what I understand for 5.1 ac3s the
'-L -3db' option is used to put the bass channel into the main stereo channels, but since 2 channel ac3s have no bass channel would this command line be accurate? '-z1 -b1 -c normal'

[Doom9]

that line is good.. but you have no gain there.. is that desired? why not use besweet with the ota gain option?

[Nightweaver]

Here seems as good a place as any ... the answer seems obvious to me, but I just want to make sure: I've noticed some movies have the soundtrack in both 2 and 5.1 channel AC3. Given this choice, should I actually use the 2-channel source to encode my mp3 or vorbis files?

[Taric25]

If you're using the Besweet GUI, in the azid settings, check that you have 2/0 selected and are controling the rear channel filtering. Also, you should check suround instead of stereo.

Since you are encoding from a 2.0 AC3 to 2.0 MP3/Ogg, you don't need the '-L -3db' option.

As for your lame settings, sterero vs. joint stereo wise, joint stereo compares the two channels and looks for similarities to arrange "what bits go where". Joint stereo preserves the phase information. Stereo just encodes the two channels seperately, however it takes complexity into account. Stereo also preserves the phase information.
So basically, if you want you channels to be as descrete as possible choose stereo, if you want higher quality sound, choose joint stereo.

As for decoding from a 5.1/2.0 file, 5.1 is typically encoded at 384kbs, and 2.0 is typically encoded at 192kbs. If we do some math the 5.1 is ~75kb/s/channel and the 2.0 is 96kb/s/channel. Both are (mostly) originally encoded from PCM streams.
If your 2.0 file is stereo, then go with encoding from the 5.1. Surround sound is more important than slightly higher quality sound (in my opinion). However, if your 2.0 file is Dolby Pro-Logic, choose the 2.0 file.

In conclusion, I choose the Dolby Pro-Logic 2.0 file, have 2/0 and control the rear channel filtering selected as welll as suround instead of stereo and encode my MP3 as stereo at (an average of) ~192kb/s VBR.

Have fun!;)