New here: Audio bitrate question

[moshano]

Hi! Just entered the world of DVD creation this monday and after finally have been able to make my first compliant DVD ( ) I have a question. Principally I'll make my DVD's from divx files with mp3 audio. Which are the bitrate equivalences between mp3 and ac3? For example, if the mp3 stream is 192 kb/s, which bitrate should I encode the ac3 with?

BTW, this site/forum is fantastic.

Thanks.

[mats.hogberg]

They have no relation. Any MP3 bit rate could be encoded to any AC3 bit rate. The higher the bit rate, the better it will sound. As neither format is lossless, you will get a (probably indistinguishable, if you go for any high AC3 bit rate) drop in audio quality.

/Mats

[moshano]

Thanks for the reply. Yes, I knew that. My question was, knowing the source mp3 bitrate, which is the ac3 bitrate with no loss in quality and no size waste (since mp3 is lossy, there will be an upper limit ac3 bitrate from which quality won't increase and will make the file unnecesary bigger)?

[mats.hogberg]

upper limit ac3 bitrate from which quality won't increase

I'd think that would require a spectrum analysis of the audio to determine its frequency (and maybe dynamics) distribution. This is (somewhat) unrelated to the MP3 bit rate, since the audio (in a 256 kbps MP3) could consist of a recorded phone conversation (narrow band, low fq) that could easily be encoded to a low bit rate AC3 with very little quality loss. Since AC3 audio is such a small part of the overall DVD data, not much is gained by lowering the bit rate, so I'd go for a high bit rate instead of scratching my head too much over this...

/Mats

[moshano]

Thanks!