I was wondering,

Many times I de-mux audio from my DVD backups, then re-encode the audio into a compressed format. Then mux them back into my DVD (which is usually in a compressed video format, like Divx).

I was wondering, in theory, if an audio CD that covers the soundtrack of my backup DVD would be of a superior or inferior quality to the extracted/de-muxed audio that was from my DVD ????

I do believe that the bit rates would probably differs, with the CD soundtrack being 44,100 and the extracted DVD audio at 48000, but I really don't know how they would differ in audio quality.

Could someone share their expertise in this for me, if they ever have made a comparison ??

Thanks,

Jon T.

If you mean a commercial 'soundtrack of movie' CD, there is probably no way to compare them directly. Mastering can be quite different, they may not even be the same recordings. If the DVD utilizes surround sound, as many do these days, that isn't even a possibility on CD.

If you mean 'make a CD-R with the extracted DVD audio content,' you will get the best quality by mucking around as little as possible with what you can grab from the DVD. Within that consideration, whether you write it on an audio CD-R or a DVD disk matter probably not at all.

Thanks a lot for taking the time to reply Andy.
That is interesting that the mastering could be very different.

Usually on a newer DVD, there will be more than one soundtrack on the movie.
Meaning that in a "setup" part of the DVD, one can select
Dolby Digital Plus, DTS or PCM Stereo.

To simplify things, lets take a 5 minute audio piece from the audio CD soundtrack that represents an
identical 5 minute audio piece from the DVD.
I assume that the soundtrack CD would be in dolby stereo in its source .CDA file format on the CD ??

I might think that one of the audio parts from the DVD could potentially sound "better" or more dynamic, depending on how it might be encoded and what it is played on.

I am ignorant how high level DVD audio gets made as compared to a standard CD .CDA that is a sountrack of the same DVD. I think usually more gets included in the DVD than on the CD soundtrack. But, that can vary.

I am thinking of the same five minute audio representation on both the CD and the DVD, just to make things simpler, and so I can understand this better.

Thanks,

Jon

Dolby Stereo is a multiplexed multi-channel encoding format for surround sound in theaters. I don’t know if it is still in use for films, but it cannot be used on audio CDs. Audio CD is strictly 2 track, 16 bit, 44.1kHz uncompressed. Dolby Surround, Dolby Pro Logic, and Dolby Digital are surround sound encoding formats. Some, or perhaps all, multiplex all audio channels onto two channels that can either be played back as standard stereo or decoded to separate channels for surround sound. Possibly the setup choice for DVD movies is simply to decide if that decoding will be done before delivering the output to your speakers.

As a thread in this forum discussed, recently published results on extensive blind testing with CD format against the same music in higher resolution SACD and DVD-A format failed to find anyone who could guess which was which under any conditions, so perceptually speaking, CD spec seems to be as good as it can get.

Actual commercial CDs very often fail to live up to that potential, however, because of mastering decisions about how best to attract the bubble gum crowd. I don’t know if that approach is often taken for soundtrack releases on CD.

The potential benefit of DVD is multi-track audio. Done well, it can be a significantly different experience but, as indicated two paragraphs above, the basic audio quality won’t be better. If a lossy compression is used on the DVD, audio quality may go down. Basic resolution will go down with lossy compression, but that difference will not always be audible.

If the commercial CD is the same mastering, its audio quality is potentially higher because audio CD is not a lossy format, but it can cannot deliver the surround sound experience. It is possible to write many other audio formats on the CD-R disk, including multi-channel versions, but they are not audio CD spec that can be played in a regular CD player.

Your first post’s statement
“ then re-encode the audio into a compressed format”
indicates a step that may be detrimental to ultimate quality. That’s why I wrote
“you will get the best quality by mucking around as little as possible with what you can grab from the DVD.”
I don’t know what kind of compression you are using. If it is lossless, simply to save space or meet some optical disk encoding specification, audio quality is not changed. If it is a lossy format, you will ensure the maximum quality by skipping the compression step, and just writing to disk, either DVD or CD, as is.

In addition to the surround sound issues, the CD soundtrack is usually an entirely different mix! When you buy a movie soundtrack CD, you usually get the music soundtrack with little or no dialog. In most movies, there is dialog and sound effects over the background music. And, some sections are completely trimmed-out so that the CD playing-time is less than the movie.

There may be exceptions for some musicals. For example Phantom Of The Opera and Evita are essentially operas (very little spoken dialog). In these cases, there isn't much need to make a special mix with the dialog deleted,. (I don't know if the soundtrack for these two movies is a special mix or not. )

There’s also the issue of different frame rates. Your usual movie is shot with 24 video frames per second with audio matching that speed. But the DVD has a framerate of 29.97/23.976 (NTSC) or 25 fps (PAL), so audio has to be adjusted. For PAL DVDs a common technique is a simple speedup including pitch shift. A well done DVD of things like Phantom of the Opera shouldn’t use such a method of course. But I wouldn’t bet my life on it.