Capturing AC3 - Stage Two

[Nelson37]

Add the Sound Blaster X-Fi card to the short list of 24-bit cards which can do this.

It also captures the MPG-2 audio thru the ATI software, even though the pass-thru audio is not connected.

DD-Wave must be captured thru the Creative Console, 24-bit SPDIF. Optical connection seems a bit better than the Coax.

AC-3 file is consistently slightly shorter than MPG audio, approximately 0.15 seconds per hour.

Current procedure is long, but it works.

Convert AC3 to temporary stereo wave with BeSweet. Using Vegas, line up waveform display with original MPG audio. Use DelayCut to add delay to AC3, and also to cut to identical duration. Then use BeSweet to convert to 6 Waves, stetch each with Goldwave using values visually determined from Vegas, then re-encode to AC3 with Vegas.

Demux captured MPG video, mux with new AC3. Cut both with MPG2Cut. Cuttermaran should work here, but it does not correctly handle my ATI files with embedded Pulldown. Demux audio and video. AC3 is rejected by authoring progs after cut, re-run thru AC3Machine using same bitrate values.

At least on DirecTV, HBO does not appear to broadcast full 5.1, all five movies capped and tested so far have been only AC-3 2.0. Bummer.

HDNet Movies, however, all five plus three episodes of Enterprise are full 5.1, LFE channel and all. Whooppee!

[Nelson37]

The time dilation appears to be pretty consistent. I had thought this may be due to the audio equivalent of dropped frames, but the problem is way too regular.

Now at four, 42 minute Enterprise episodes, each one right at 0.10 seconds short. The limit of accuracy is approximately 0.02 seconds, so even with that this is too consistent for a random dropped frame issue.

The stretch procedure is working fine, the new 5.2 Goldwave is dramatically faster and batch processing available for the Time Warp effect.

[Nelson37]

The time dilation is apparently caused by the BeSweet AC3 to WAV conversion. It slows down the AC-3 by 0.10 seconds Per 45 minutes (approximate) with each run.

Unfortunately, since the AC-3 capture is started at a different time, and I can't see an AC3 waveform in anything I have tried, I have to do it at least once.

Simplified Procedure - Convert DDWav to AC3. Edit captured MPG with MPG2Cut2. Convert AC3 to 6 waves. Mux front and rear channels for Vegas. Load MPG and Front, Center, LFE, and Rear into Vegas. I move the MPG audio down to the Voice channel. Visually align, split, and cut to match. Stretch Waves to align exactly. Cut MPG track, create new AC3. Demux M2v and mux with new ac3 file.

Works great, good synch, no problems.

Also confirm HBO on DirecTV is only Dolby 2.0. HDNet and HD Theater are full Dolby 5.1.