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Audio Sync - AJA, how is this supposed to work?

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Eric Hansen
Audio Sync - AJA, how is this supposed to work?
on Apr 30, 2010 at 8:16:42 pm

some of you may remember me posting about audio sync issues with the LHi and a HDMI-connected audio receiver and projector:

http://forums.creativecow.net/thread/98/875682

basically every piece of equipment had a latency and i had to match them. everything is good now. but a few questions popped up over how FCP and the Kona cards handle audio.

1. There's a frame offset in the System Settings preference pane. when you adjust this, the Canvas window will delay by this many frames to match whatever delay is inherent in the video card (AJA says their cards have no delay, so this should be zero) and whatever delay is in your video monitor (CRTs have no delay, but LCDs do).

2. no adjustments in FCP or Kona Control will affect audio. all audio outputs are locked together and cannot be delayed (an AJA tech confirmed this)

a few years ago, all of my installations either had a CRT as a monitor, or no monitor at all. so i never had to worry about the frame offset setting. now LCDs are becoming the norm, and these units have latencies. my question is, if 95% of the video monitors now have latency (LCDs), doesn't this mean that 95% of editors (using LCDs) are experiencing video out of sync with audio? (this assumes that both the video and audio are coming out of the Kona card. if you connect your audio system to the output of your broadcast LCD, it will be delayed to match in the internal delay of the LCD - Flanders Scientific confirmed this for me)

since it took a 5 frame offset to get my FCP timeline to match my projector, i have added a 205ms delay to my audio monitors.

i'd really like to hear anyone's take on this, especially AJA. every tech i spoke with was stumped by this.

thanks

e

Eric Hansen - http://www.erichansen.tv


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Jeremy Garchow
Re: Audio Sync - AJA, how is this supposed to work?
on Apr 30, 2010 at 8:59:08 pm

[Eric Hansen] "if 95% of the video monitors now have latency (LCDs), doesn't this mean that 95% of editors (using LCDs) are experiencing video out of sync with audio?"

Probably. I monitor the output of the LCD for sync.

You can delay audio by manually knocking the whole sequence out of sync, sometimes necessary for geometry or frame rate conversions.


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Eric Hansen
Re: Audio Sync - AJA, how is this supposed to work?
on Apr 30, 2010 at 9:04:39 pm

Jeremy wrote: I monitor the output of the LCD for sync.

just to clarify, you're monitoring your audio on the output of the LCD itself?

e

Eric Hansen - http://www.erichansen.tv


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Jeremy Garchow
Re: Audio Sync - AJA, how is this supposed to work?
on Apr 30, 2010 at 9:10:50 pm

Yes. To ensure sync, yes. So Kona HDSDI out to LCD, then output of LCD to mixer and most of time I monitor that signal, but also have the output of the Kona sent to mixer as well.

Jeremy


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Doug Beal
Re: Audio Sync - AJA, how is this supposed to work?
on May 1, 2010 at 4:11:32 pm

On the FSI monitors there is an audio output from SDI input de-embedder.
That's what we monitor in DS, FCP matrox.
On the KONA3 and LH systems we see now sync issues watching the SDI out and monitoring AES D>A audio

Doug Beal
Editor / Engineer
Rock Creative Images
Nashville TN


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Eric Hansen
Re: Audio Sync - AJA, how is this supposed to work?
on May 1, 2010 at 5:05:23 pm

i think i'll switch to the FSI's audio output so i can stop using my digital delay (it likes being on my guitar's pedal board more than in an edit suite). i just wish that the FSI monitors had something better than a 1/8" socket for the audio output.

but what do you think i should do about the edit suites that have LCD monitors like Apple Cinema displays attached to HDLinks and the like, instead of broadcast monitors? for me, these are the majority of the edit suites i work in. only my color correction suite has the FSI.

thanks

e

Eric Hansen - http://www.erichansen.tv


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Doug Beal
Re: Audio Sync - AJA, how is this supposed to work?
on May 3, 2010 at 7:51:45 pm

Being those LCD displays you're talking about have no way to show both fields you could have issues you are not aware of and cannot see. The FSI will show you both fields provided your setting in the AJA control Panel is set to pause on full frame in the Codec tab
That being said the HDlink has a pair of RCA outs for monitoring.
I agree re monitoring unbalanced audio is a pain but remind yourself it's just monitoring for sync purposes, and it will give a pretty fair simulation of how most folks are going to hear your program.

In my previous post I meant to say No sync issues not "now" big difference that one letter
Good Luck

Doug Beal
Editor / Engineer
Rock Creative Images
Nashville TN


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Eric Hansen
Re: Audio Sync - AJA, how is this supposed to work?
on May 3, 2010 at 8:11:19 pm

Doug wrote: "the HDlink has a pair of RCA outs for monitoring"

these outputs won't take into account whatever latency the LCD monitor itself has.

i don't know if a lot of post houses run into these issues, but i work with a lot of editors that cut on the beat of the underlying music. so if the sync is off by even a few frames, it's very noticeable.

e

Eric Hansen - http://www.erichansen.tv


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