View Full Version : Real-time audio sync

Rick Green
04-16-2003, 04:17 PM
We're using our toaster as a switcher, cg, etc. for our linear edit system. The great majority of our work is done on two Avid systems, but there is still an application for some linear editing. Here's the problem: My boss just finished a 20 minute program on our new Toaster. We worked through the various bugs and software upgrades and thought everything was OK. He made a safety dub on Beta SP running back through the Toaster, and we all realized that there is a very noticeable video delay on that second pass.

In fact, if you look closely on the first pass, you can see it. It's probably a frame or two. We sent a few pieces of the first pass out to a high-end post facility, for some additional work and they saw the delay as well. On the second pass, there's no question about it. Because we have multiple sources and a very adequate outboard audio board, we are not running any audio through the audio portion of the Toaster. My questions:

Is there a similar delay built into the audio section to keep everything synced up? Should I pass the output of my audio board through the Toaster to match the delay? Finally, if the Toaster audio board will want to follow the switcher video, I'll need to defeat that feature somehow.

04-16-2003, 04:54 PM
Re: turning off audio following switcher, see the picture I'm attaching.

See where it says

Switcher Follow/Off.

That's where you turn that feature on/off. For your needs, just play with the audio setting till you're comfortable and then keep that setting I just told you about off.

As the source of the problem you're seeing, I'm sorry but I don't have knowledge of that.

Hope this helps while you try to figure out the root of the problem.

BTW: Is the delay constant throughout the video?


Dick Nelson
04-16-2003, 08:14 PM
Yes, the Toaster delays audio and video and I think if you don't run the audio through the Toaster, too, they would not be in sync. In our system, which we use for as-live production, we run all external sources through an outboard mixer, the output of which goes into one Toaster audio input. Then we record the output of the Toaster audio mixer. Some of these exterior sources are connected to their own monitors. If you play a tape and have the monitor volume turned up, you will notice an "echo" effect because the audio going through the Toaster is delayed, while the audio straight to the monitor is not.

Paul Lara
04-17-2003, 05:45 AM
Originally posted by Rick Green
Is there a similar delay built into the audio section to keep everything synced up?

Yes, Rick, the audio and video streams are both sent to system RAM, where they are locked together and sent to Program Out.

As a switcher, the delay is necessary to make sure all frames are synchronized with audio and time-base corrected. Once you route your audio through the Toaster, it'll synch perfectly.

04-17-2003, 07:26 AM
Alternatively, if you REALLY want to bypass the Toaster's audio for some reason, I can't think of any reason you couldn't simply introduce a digital audio delay unit into the external audio circuit with similar results. The Toaster has something on the order of 3-4 frames of latency at the moment, and it should be pretty simply to compensate for that.

04-17-2003, 11:59 AM
VT video passing through has anywhere between a 2 and 3 frame delay, if your video sources are genlocked to VT output, or it will be two frames.

Audio passing through the VT has the same delay as the video (more precicely, 75 ms). In a linear edit situation, you will probably want to pass the audio through the VT, or at least some other delay mechanism to get it to match up.