questions about quality of different formats etc

[inferno6a]

Hi. I am a newbie in these areas.Any response except flaming will be appreciated.

1. If i am to transcode a cbr 128 kbps mp3 audio to a format that is compatibile with dvd-video,should i use ac3 or mp2 and at what bitrate, if the maximum bitrate I can allow is
a) 192 and b) 256? (for different dvds)

( I know transcoding a lossy to another will suck etc but I just want to know which is the better of the 2 when my bitrate limit is 192 or 256 , they can both suck compared to the original for all i care)


2. I read in forums here and there that ac3 stereo has trouble providing the same quality as mp3 unless its of a much higher bitrate, is that true?
If it is true, why is ac3 still so popular if it is "less efficient"?
Even the next generation of video media seem to be using it as a standard.

3. Just for fun and testing purpose, I encoded a 448 kbps stereo AC3 file from a uncompressed stereo audio source with the latest besweet beta and the final audio contain hissing(at least i think its called hissing :p ), is there any reason for it?
(wrong setting,program imcompatibility etc)
Tried with another few lossless audio and most of them are affected to the same extent.
What i do is just
[ BeSweet.exe -core( -input "path\1 Musoka.wav" -output "path\1 Musoka.ac3" -logfile "path\1 Musoka.log" ) -ac3enc( -b 448 )]

http://www.badongo.com/file/2030210

4. Is AAC better than AC3 at a bitrate around 400 to 600 kb or equal or inferior?


Thanks for reading. I have little to no knowledge of such issues and I know the common "use your own ears" or "just keep it in its original format"reply. But just want to know the some opinions even if there is no "correct" answers to some of my questions..

[Blue_MiSfit]

As you know and state, It's hard to answer most of your questions. The real answer would ultimately be 'try it and see what you like better'.

Some important information regardless:

Dolby Digital (AC3) is a very powerful format which is well suited to handling film sound tracks. One of these features is its metadata support of dynamic range compression (DRC). This lets you adjust the sound track on the fly to suit your listening environment. For example - a quiet house at night with sleeping housemates is a situation where an even volume level is ideal. No loud explosions to wake everyone up, but still loud enough to hear whispered dialogue (strong compression). The opposite would be a full range environment like a movie theater or a good set of headphones, where you want to hear it all (little or no compression). This flexibility is lacking from MP3 and other typical audio compression standards.

Dolby Digital also works very well with multichannel content. MP3 to the best of my knowledge does not do this in a standard, well supported way. Finally, Dolby Digital is supported by a lot of home theater receivers, which means that you can pass a digital signal to your amplifier, and let its onboard decoders and DACs handle the processing instead of most wimpy DVD players. You can also send a full 5.1 signal in one cable, much better than 6 :)

Then again, people don't generally use AC3 for backing up music CDs, because it's not really designed for that. MP3, AAC, Vorbis, and FLAC are all very good with this kind of content.

One thing to keep in mind is that IIRC, most freely available AC3 encoders don't hold a candle to a pro commercial encoder. I may be wrong though :) AC3 is AFAIK always CBR, so it's not going to be as efficient as a tight LAME MP3 or AoTuv Vorbis. Freeware MP2 encoders on the other hand are mature and capable at this point. For this reason, when burning DVDs from content that has originally MP3 audio, I generally use MP2 at the standard 224kbit. If you've got lots of bitrate to burn (like 30 minutes of video on a DVD5) then, you can use uncompressed WAV, which will preserve all the quality of your MP3 source - AKA no recompression = good :)

Finally, if you're ok with having your CD's backed up at ~500-600kbit, then just use one of many lossless codecs like FLAC/Monkey Audio or Apple's ALAC (if you use an iPod). When you decode, it's mathematically identical (or absurdly close) to the raw uncompressed WAV you feed it, but it's around 500-600kbit usually, as opposed to ~1500kbit for 2ch 16/44.1 PCM.

[tebasuna51]

I agree with Blue_MiSfit post, and:

- You can use DivX-DVD standalone players (not expensive now) with avi container (MPEG4 video, MP3/AC3 audio) instead DVD format (MPEG2 video, MP2/AC3 audio). You don't need transcode the audio and uses a more efficient video codec.

- The new codecs are more efficients at low bitrates but equivalents at high bitrates. For instance a mpeg4 (DivX) video at 4000 Kb/s is similar to a mpeg2 video (DVD), but is clearly better at 1000 Kb/s. Same with audio codecs, then we can compare the codecs/bitrate (more or less, source dependent, different opinions, talking only of actually/future compatible codecs, stereo audio, ...):
aac 98 Kb/s ~ mp2/mp3 128 Kb/s ~ ac3 192 Kb/s

- Now answers to your exact questions:

1) Like you say, a transcode always is worse than original, then for a mp3/128 Kb/s is enough mp2/128 Kb/s or ac3/192 Kb/s

2) For only music I think mp3 is most popular than ac3. For audio movie tracks ac3 support multichannel , is a old standard in DVD format, support DRC, ... (see the Blue_MiSfit post).
"Even the next generation of video media seem to be using it as a standard". You know, the industry don't see only technical reasons (aac is more appropriate to be the next standard) but commercial ones.

3) Free ac3 encoders are worse than commercial ones, BeSweet-ac3enc is not recommended (see the FAQ). Now there are a free encoder in development stage, but usable better than ac3enc, is Aften (http://forum.doom9.org/showthread.php?t=113074). The bitrate recommended for stereo audio is 192 Kb/s, 448 Kb/s is recommended for 5.1 multichannel.

4) AAC versus AC3. The bitrate must be referred with channel number, then for stereo: 98 Kb/s aac ~ 192 Kb/s ac3, for 5.1 multichannel: 224 Kb/s aac ~ 448 ac3.
Then, for a stereo audio, 98 Kb/s ac3 is worse than 98 Kb/s aac, 224 Kb/s ac3 is near to 224 Kb/s aac (at high bitrates all codecs are near). The max bitrate for aac encoders (Nero, CT) is 320 Kb/s then we can't compare 400-600 Kb/s (the max bitrate for ac3 is 640 Kb/s and is used only for multichannel)

[inferno6a]

thanks for the reply. So I can assume if I convert to dvd video with my bitrate limitation using mp2 for < 192 bitrate is more advisable than ac3 and when my limitation is 256 both ac3 and mp2 will serve me well?
( and some of my shows are h264 and some in mkv/ogm/avi containers etc so most standalone players don't fufill all my needs.)

This may be in the wrong forum but I am going to ask anyway.(mods can remove it if its inappropriate)
1. is ac3 audio vbr or cbr or can be both?
2. When you watch ac3 5.1 dvd using a dolby prologic 2 decoder set that is nt equipped with dolby digital (rare i know but for curiousty sake or if an optical cable goes missing), will you get "true" pl2 audio like from a dpl2 encoded track? As in the dvd player will output dpl2 stereo signals from the 5.1 ac3 track. Remember reading this is true somewhere but forgot about it.

[HeadBangeR77]

thanks for the reply. So I can assume if I convert to dvd video with my bitrate limitation using mp2 for < 192 bitrate is more advisable than ac3 and when my limitation is 256 both ac3 and mp2 will serve me well?
( and some of my shows are h264 and some in mkv/ogm/avi containers etc so most standalone players don't fufill all my needs.)
Yeah, in general, but the point is, there are no fully stable non-commercial AC3 encoders. The one you've already tried to use is crappy, Afteen is getting more mature, but can't be described as "fully stable" imo. On the other hand mp2 encoders are free & mature enough, so I would use mp2, if I were you ;)

This may be in the wrong forum but I am going to ask anyway.(mods can remove it if its inappropriate)
1. is ac3 audio vbr or cbr or can be both?
AC3 is CBR always.

2. When you watch ac3 5.1 dvd using a dolby prologic 2 decoder set that is nt equipped with dolby digital (rare i know but for curiousty sake or if an optical cable goes missing), will you get "true" pl2 audio like from a dpl2 encoded track? As in the dvd player will output dpl2 stereo signals from the 5.1 ac3 track. Remember reading this is true somewhere but forgot about it.
I haven't got the faintest idea, wait for the gurus to answer you ;)
cheers

[tebasuna51]

thanks for the reply. So I can assume if I convert to dvd video with my bitrate limitation using mp2 for < 192 bitrate is more advisable than ac3 and when my limitation is 256 both ac3 and mp2 will serve me well?
Like HeadBangeR77 say use always mp2 for stereo audio.
Convert only to ac3 the 5.1 (maybe aac) audio.
(and some of my shows are h264 and some in mkv/ogm/avi containers etc so most standalone players don't fufill all my needs.)
You always can recode h264, aac, ogg to DivX/Xvid, mp3/ac3 and use standalone player compatible avi's, better than transcode to DVD format (mpeg2, mp2/ac3). At least you need 1/3 of bitrate for same quality.
1. is ac3 audio vbr or cbr or can be both?
Only CBR.
2. When you watch ac3 5.1 dvd using a dolby prologic 2 decoder set that is nt equipped with dolby digital (rare i know but for curiousty sake or if an optical cable goes missing), will you get "true" pl2 audio like from a dpl2 encoded track? As in the dvd player will output dpl2 stereo signals from the 5.1 ac3 track. Remember reading this is true somewhere but forgot about it.
If I understand, you have an audio equipment with dpl II decoder and stereo input only (without optical input or 6 separated input channels), but surround speakers. Really I have a old one like this but only dpl I decoder.
When you play an ac3 5.1, from dvd or avi, the player must be configured to downmix the 5.1 to 2 channels dpl II encoded.
If standalone player -> Check if is possible by Config options.
If PC soft player -> Configure your DVD players (PowerDVD, WinDVD,...) and your audio players (ffdshow, ac3filter, Foobar2000, WinAmp, ...).