stereo/mono quality and bitrate

[AlanHK]

I have an AVI file with a mono soundtrack that I want to author to DVD.

I make the AC3 soundtrack by piping the audio from an AVS into Aften, at a bitrate of 128 kb.

for %%I in (%1) do (
wavi %%I - | p:\aften\aften.exe -b 128 -s 1 -w 45 -dnorm 27 - %%~nI.ac3)

That gave me an AC3 file size 88 MB.

I was concerned my authoring software might not handle mono gracefully, so I added this line to the AVS:

MonoToStereo(last,last)

Then running exactly the same command gave me a (stereo) AC3 file, also 88 MB.

Though I can't hear a difference, I assume that the quality is actually lower for the stereo file. Is that correct? Is it true that each track is effectively 64 kb rate, or is it more complex?

[Southstorm]

Since it started as a mono clip, and has no stereo shaping to it, I doubt you're really loosing anything. The files are both 88mb because the bitrate didn't change. You are correct in assuming that each track L/R is now 64kb in stereo. If you can't hear any diiference, I'd go for it.

[AlanHK]

OK, thanks.

[tebasuna51]

Though I can't hear a difference, I assume that the quality is actually lower for the stereo file. Is that correct? Is it true that each track is effectively 64 kb rate, or is it more complex?
A little bit more complex. See this Aften parameter:
[-m #] Stereo rematrixing
0 = independent L+R channels
1 = mid/side rematrixing (default)

If you use -m 0, then each track is 64 kb rate, but the default is use "mid/side rematrixing" and with two exact channels the bitrate can be near 128 Kb for the "mid" (common) part.

[AlanHK]

If you use -m 0, then each track is 64 kb rate, but the default is use "mid/side rematrixing" and with two exact channels the bitrate can be near 128 Kb for the "mid" (common) part.

Good. I was hoping something intelligent like that was going on. So I wasn't wrong on thinking there was little difference in quality.