LPCM to ? to AC3

[qlizard]

If I ultimately plan to convert to ac3 in TMPGenc Dvdauthor when I create DVDs from home videos, should I keep the audio as LPCM when I encode the files? I use procoder.
In other words, would the quality ultimately be worse if I converted to MP2 during encoding before converting later to ac3 during authoring? If it doesn't make a difference, I would rather encode them with MP2 for the space savings because I will probably keep the mpegs on the hard drive for awhile.

[jaxxboss]

I dont think the difference is all that much, plus converting from mp2 to ac3 will be easier for you as you can pretty much know how big to make your mpeg2 files. With lpcm as they are so much larger you'll have a hard time getting the most out of your video...unless you then want to add a step and shrink it to fir a dvd. You can encode u'r mpeg2 with lpcm up to 4.3 gigs, but then when u author to ac3 your file will be so much smaller and u'll waste space that could have gone to the video.

Heck, even with encoding with mp2 to 4.3 gigs and then authoring it to ac3, you'll still have a bunch of room to fart around with for the menu or whatever.

[lordsmurf]

Double compression will harm the fidelity. Convert least amount as possible.

[qlizard]

Convert least amount as possible.

LS,
intuitively I would think the same thing. But I'm not familiar enough with how AC3 and mp2 are compressed to know whether or not the quality loss is compounded. Are you stating the above in general terms, or have you seen (or heard, I guess) quality loss doing this in practice?
thanks

[cdcox]

I would leave the audio as lpcm and convert to ac3 for best sound quality. as far as knowing what bitrate would be, using a bitrate calc would help with that. I would input the video length and bitrate for audio that you want to use and see what the video bitrate would be. For example if you tell the calc you have a 60 min video and you plan to convert the LPCM 1536kbs audio to 384 kbs ac3, tell the calc your audio bitrate is 384 kbs. It will give you a video bitrate that should keep the total bitrate correct to come out to the correct size for a 4.7g disc.