Ext sync

[smashprod]

Because I come from the film scoring world, I've always used external video sync (house sync) for my audio system (a couple of old 2408s and a DTP). I have a Horita black burst generator for that.

Here's the quirky part. Both my master and slave Macs are older 8-core (Harpertown) models which can output video through their ATI Radeon HD 2600 AT video cards. I send that video output to an LCD TV monitor, which I use as a second screen for Quicktimes. I don't use a 2nd computer monitor because I'm fine with the streamers and punches feature of the DTP and don't want to waste CPU power on letting DP generate them and superimpose them. SO-- I use a video A/B box and switch the video input of the DTP from black burst (Horita) to the video output of the TV. Everything works fine, no problem-- but is the video signal from a TV (a Sharp LCD) inferior to the Horita, to the point that it would degrade the audio through increased jitter? I don't notice anything, but really want to know if I'm asking for trouble.

And, for that matter, would it improve the audio to either use the 2408's internal clock, or to use a piece of higher-end gear as an external clock (I have an original Apogee RosettaAD)? I know I'm diving right into the controversy over clock jitter, I'm not asking about the fine points though.

Thanks-
David

P.S. I moved this over from the main DP forum

[4stripes]

Most technical folks would agree that using the internal clock is generally better than an external clock. If one does not agree, I'd offer that it also makes technical sense.

I don't really understand your question. Only an NTSC black burst signal should be used for video sync. You're using some random coax of a TV, and switching it in the middle of a session? That doesn't make sense to me.

I wouldn't worry about jitter. For one, it doesn't sound like you're doing any recording, just mixing. Jitter doesn't permanently alter digital audio after it's been recorded.

If you don't want to worry, just get a good DAC like Benchmark or Lavry. External audio clocks are for dopes. The problem with external-clock-types, is they aren't asking the finer points, they just don't care. It'd be too much thinking. If you spend $3000 on something, you'd sure like to believe it does something useful. One finer point being, when you use an external clock, you are relying on your "bad" converter clock's PLL to lock instead of it's clock. Why would the PLL of a bad converter be better than it's own clock. It doesn't make sense.

[smashprod]

Thanks 4 Stripes.

What I meant was that I would use the video output of the TV as a clock whenever I was working on a project with picture (both recording AND mixing). I would use the Horita as the clock for audio-only projects. I was hoping that the TV's video output might be as stable time-wise as the Horita. Sounds like that's dodgy. And that using the internal MoTU clock might be better than using black burst.

[4stripes]

Do you have other external gear that requires vid ref or is a timecode master? If not, you don't need black burst at all. Just run your session internal. It sounds like your use of vid ref may be redundant.

[smashprod]

Now that I think of it, you're right. Using Black burst is a remnant of when I used to score to videotape - you don't know anyone who wants a used Panasonic AG-7650, do you?

[4stripes]

It's good to stop and think of it every once in a while... one often saves money and headache that way! More is not always more.