If I try to edit surround audio, video is no longer in sync with audio

riredale wrote on 7/28/2004, 3:18 PM
I came across a curious effect. As long as I work with the "Microsoft Sound Mapper" in the Preferences/Audio Device window, then video and audio are in sync. In order to get the surround panner, however, I need to select the "Direct Sound Surround Mapper" and after I do so, the video can be out of sync with the audio track(s) by perhaps 10 frames. Sometimes it's in sync, but most of the time it's not. What I mean by "being out of sync" is the video as shown on the preview window. The actual avi file still has sync between audio and video.

What am I doing wrong?

Comments

JaysonHolovacs wrote on 7/28/2004, 9:51 PM
Hmm, maybe it's latency in the DirectSound Surround Mapper? I'm actually using that too, but I'm mostly syncing to music, so perhaps I don't notice. Or perhaps it has to do with your sound card driver's support for DirectSound. Get the latest sound card drivers if you haven't, and maybe the latest DirectX if you don't have it(I think DirectSound is included in DirectX).

Are you doing RAM preview, or trying to play it live? If you are playing it "live", then maybe the system just can't keep up with the surround envelopes you've set up.

-Jayson
Spot|DSE wrote on 7/29/2004, 1:41 AM
You should be in sync all the time. Jayson's on the right track...you should be using either Classic or Asio drivers, depending on your audio card. If the card has ASIO drivers for it, use those.
JaysonHolovacs wrote on 7/29/2004, 6:46 AM
Spot or anyone,
Forgive me for being naive, but what are ASIO drivers? Where can you find them? And do they tend to be available for consumer grade sound cards? I just have a (don't laugh pro guys) SoundBlaster Audigy. It looks like I can do MS or DirectSound drivers, unless there's someplace I can get the drivers you suggest?

-Jayson
farss wrote on 7/29/2004, 7:18 AM
ASIO drivers give much lower latency, don't know the precise specifics but I assume they bypass much of the Windoz stuff so the app can do I/O directly to the hardware and hence reduce latency.
They're not without there downside as I understand it. Due to lower levels of buffering it's harder for the processor to keep up so you can get gaps in playback. I've never struck this issue myself so I'm always running the ASIO drivers although one oddity (which kind of makes sense) is Wondoz itself has trouble getting its 'Dings' and 'Bongs' out.

The other thing I do notice with the ASIO drivers is when I hit play for the first time I loose about the first second of audio. Subsequent stop / plays are usually fine, just the first one, kind of like a pipeline needs to get filled up before the data makes it to the sound card.

Bob.
JaysonHolovacs wrote on 7/29/2004, 8:44 AM
Thanks, farss, do you if and where I could get them for my sound card?

-Jayson
riredale wrote on 7/29/2004, 10:55 AM
Okay, gang, thanks to all for the feedback. I've solved my problem.

First of all, here was the issue: the only way I could get separate 4-channel audio from my TurtleBeach Santa Cruz audio card in Vegas was to use the "Direct Sound" mapping in the Preferences/Audio Device selector. The other two choices, "Microsoft Sound Mapper" and "Windows Classic Wave Driver" would deliver audio, but the rear channels would be folded into the front speakers. Only Direct Sound would give me four discrete audio channels that mapped to the Surround Panner correctly.

But here was the problem: in the Direct Sound mode, the audio and video (as seen in the Preview window) lost sync, and the delay was inconsistent. I also noticed that the audio level meters seemed very sluggish much of the time. So I had a choice of keeping audio and video in sync while editing, or getting that glorious surround sound that I sweated blood to capture.

I discovered a newer driver update for the Santa Cruz card, but it gave no improvement. I guess I could have dumped the sound card for a more exotic one, but I've grown rather fond of it and its very nice equalizer.

Then, a little voice in my head suggested I check out the DirectX pages. Typing "dxdiag" in the Run command line brought up the DX diagnostic pages. Checking out the audio page, I saw that the Hardware Acceleration slider was all the way to the right. I experimented with the other positions.

Shazam!

With the slider in either of the two middle positions, video and audio are now in sync. With the slider all the way to the left (no hardware acceleration at all), Vegas crashes when trying to play the audio.

Which makes me wonder: just what does DX do in that extreme right position in addition to the next position over? What is "Full Acceleration" as opposed to "Standard Acceleration?"

A few months back I solved a jerky-DVD-playback issue on my Dell laptop by moving THAT hardware-acceleration slider one notch leftward also. So I guess you can have too much of a good thing when it comes to DirectX.

Another note: when probing around the TurtleBeach web site, I came across a query about ASIO support. Their response was that it was not necessary, since Microsoft has introduced a new low-latency approach called "Kernel Streaming." Anybody know anything about this?