I know we've had a couple of PMs since this was originally written, but I want to go ahead and reply to it in full right now, be sure you have all the information you need on the topic....
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I have the audio files saved as CD-quality WAVs (PCM, 44.1 KHz, 16-bit stereo)
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Not the best solution. Since DVD audio is 48kHz, it should be left in this format. Resampling the audio froim 48kHz to 44.1kHz and back to 48kHz is somewhat harmful to the quality.
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I’m using MPEG Video Wizard for very minor video editing first, and will then lay the clean soundtrack over the dirty one.
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This is a good method, assuming you're not letting Womble re-encode the video. MPEG editors are very accurate for editing, yet not having to decode/encode the subsequent video file that you save.
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Video: MPEG-2, 720x480, 29.97 fps, 9800 kbps (vbr)
Audio: Linear PCM, which locks at 2 channels, 48 KHz, 1536 kbps
I have my video at 9800 VBR to maintain quality; MVW will export it as BLUE “100% Stream Copy,” so I feel I’m ok. I haven’t tried anything different so I don’t know if lowering it to, say, 9000 VBR will force a re-encode or not.
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If this came right off a DVD, then the 9800kbps is more likely the maximum bitrate flag attached to the stream. Depending on the length of the recording, it's probably not anywhere close to that. For example, a 2-hour DVD would be more along the lines of 5000-5500kbps on a single-layer disc. To learn the real bitrate, you'd have to see the video in a bitrate viewer. The newest versions of GSpot Codec Appliance (v2.70) scans and shows the actual average bitrate of the file.
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As for the audio, PCM unfortunately requires a near total re-encode. While the results are great, I do hear a small difference on good speakers. I’ve tried first converting to both MP2 and AC-3, but to my ears they’re much worse than the re-encoded PCM – before I even mux them with video. I used ffmpegGUI for that and wasn’t impressed.
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Muxing should have no affect.
Compression can distort and damage already-touchy audio, at times, yes. I've heard it too, it's not our imagination. The solution, however, often lies in simply pumping up the bitrate on the audio, such as 384kbps AC3, using a good AC3 encoder. I would not consider the freeware AC3 encoders good enough for this specific task, though they handle excellent audio perfectly fine. The AC3 encoder in
TMPGEnc products, or Ulead products, for example, would do quite nicely. It really depends on what you have.
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1) Do you have any suggestions for “adjusting” the PCM audio before hand, so it will fit MVW’s locked setting and won’t re-encode?
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It might be worthwhile to do your editing, save the project, then highlight the entire AUDIO line, and delete it. Export the video only. When finished, use the back arrow to undo (or press CTRL+Z on keyboard) and this time delete the video. Just export the audio as PCM. This will give you both streams separately. Encode the PCM to AC3 in something better, be it the authoring software or a dedicated pro AC3 audio encoder. I use the AC3 encoder in the aforementioned
TMPGEnc DVD Author, Ulead DVD Workshop 2, or
Adobe Premiere Pro CS3. Does your Vegas install have AC3 as an option?
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2) Is there any reason Mac won’t recognize the audio of a PCM MPEG? Perhaps because the source is WAV?
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More stupid Mac vs Windows junk
(thanks MS + Apple, way to help your customers!), MacOS expects an AIFF container and not a WAV one, for its PCM audio. I can do this in
SoundForge.
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2) Should I be concerned about those bit/sample rates with such large MPEGs (each comes to about 1.25 GBs) under the above hardware conditions, even if I max out the capacity of each disc? What about good quality dual-layer discs like Verbatim?
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If your PCM discs are coming out sounding and looking fine, then I really wouldn't worry much about it. Especially don't worry if this is for yourself or friends/family, and not professional distribution to thousands of unknown (and potentially picky) players.
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3) Will the audio be ok once it's re-encoded, yet again, in Architect? Or can I somehow avoid that re-encode too?
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It all depends on whether it's really being re-encoded or not. It would be fine converted to AC3 at 384k, it might still be transparent at PCM 1536k.
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4) Is it possible playback issues can occur at anytime, since the bitrates vary? Or can I rest my mind once each disc checks out ok?
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The worst that would happen is the player freezes or skips, confused by high bitrates. If you think it's working fine, and as mentioned above, are not distributing professionally, then I'd not be overly concerned about it.
I'm not really sure you're even coming close to bitrate spikes. If this is at least an hour long, and a single-layer disc, it won't spike that high. The video bitrate spike can also depend on the encoder, some of them simply will not go much above 8000kbps, even when instructed to do so.