Audio before video? at DVinfo.net

Chris Thomas · September 4th, 2004, 10:46 PM

I just finshed a recent edit of a 10 minute shoot, with my GL2 and a shotgun, from about 10' away from a podium, and I found that the audio was 4-5 frames ahead of the video. It did not drift, it was the same sync start to finish.

I ran the original tape direct to a TV to see if it was a capture problem, but the sync was out there too...

Obvoiusly easy to correct in post, but is it a common problem?

Mike Rehmus · September 4th, 2004, 11:54 PM

Sound travels much slower than light. so if anything, the audio should be 3-4 frames behind the video. Ahead doesn't 'sound' right at all.

Let's play with some numbers. Assume sound travels at 700 mph. Using 'close' numbers for quicker calculations:

700 x 5000 feet (mile) = 3,500,000 feet per hour. Divide by 60 to get feet per minute = 58,333 fpm. Divide by 60 to get feet per second = 972 fps Divide by 30 to get feet per frame = 32 feet.

So, using these rough numbers, for every 32 feet away from the event you set your camera, an on-camera microphone will record the audio one frame later that it actually occured. If you use a wired or wireless microphone located at the event, there is no delay of course.

I think that you need to look for another answer if your audio is leading your video

Robert J. Wolff · September 5th, 2004, 06:15 AM

How about trying a head cleaning? Could be a small build up is your problem.

Just a thought.

Bryan Beasleigh · September 5th, 2004, 08:40 AM

<<<-- Originally posted by Robert J. Wolff : How about trying a head cleaning? Could be a small build up is your problem.

Just a thought. -->>>

Dirty heads would cause drop outs , not a timing problem. This is a real time issue and I can't see how the camera could be at fault.

Robert J. Wolff · September 5th, 2004, 08:57 AM

Bryan,

As I said it was just a thought. My thinking is that the video portion of the head, could be clogged enough to "lift" the tape as the video is laid down, possibly forcing audio to lay down earlier.

It was just a slim chance that cleaning the head might correct the problem.

If tried, and it does not correct the problem, Chris may have to take it to the camera doctor. The only other item that comes to my mind, is time-base correction has changed some how.

I would be interested in hearing from Chris as to what it takes to solve the problem.

Chris Thomas · September 5th, 2004, 09:50 AM

It is very strange indeed. I have had issues with the audio behind in the past, but that was when I was quite far from the source, and I realized that that is just how it works (Thanks for the ft/frame calculations Mike!)..

I have not used the camera again since, so I will do a few test tonight and see if it was some type of fluke, or a problem that is still there. I guess if it exists, I will have to send my baby away :(

Mike Rehmus · September 5th, 2004, 11:33 AM

Canon, at least in their earlier cameras, didn't follow the rules with regard to handling the video/audio interleave with the result that special consideration had to be incorporated into NLEs to accomodate the issue.

I've not heard of those cameras inserting the audio before the video, though. It was always a few frames after the video and in a burst so the audio could catch up.

Might be interesting to post a question about audio embedding in the GL2 forum to see if anyone recognizes the problem.

Just out of curiosity, you are running 16 bit audio into channels 1 & 2 and haven't somehow switched the camera to 12 bit, insert audio into channels 3 & 4?

Jacques Mersereau · September 5th, 2004, 01:57 PM

<<<-- Originally posted by Chris Thomas : I just finshed a recent edit of a 10 minute shoot, with my GL2 and a shotgun, from about 10' away from a podium, and I found that the audio was 4-5 frames ahead of the video. It did not drift, it was the same sync start to finish.

I ran the original tape direct to a TV to see if it was a capture problem, but the sync was out there too...

Obvoiusly easy to correct in post, but is it a common problem? -->>>

What deck or camera are you using for playback (same one to record?)?
What speakers?
What monitor?

If you used a shotgun, how did you get the signal into the camera?

Did you record at 16bit/48Khz or 12b/32K?

I don't own a GL2, but the GL series is known for mis aligned heads.

Have you had this issue before, or just on this shoot?
Have you ever used the shotgun on a different gig and had the same issue?

Chris Thomas · September 5th, 2004, 09:34 PM

Quote:

What deck or camera are you using for playback (same one to record?)?
What speakers?
What monitor?

I used the same GL2 for playback of the original tape on my TV. I only noticed the problem after the edit, for which I use a Sony DCR-HC20 as a deck, and to connect to an external monitor. After seeing the problem in the edit, I checked the raw footage and saw it there too.

Quote:

If you used a shotgun, how did you get the signal into the camera?

I use an XLR to Mini 1' cable

Quote:

Did you record at 16bit/48Khz or 12b/32K

16bit record, capture, and output, no audio changes on the camera during recording or capturing. All 16bit.

Quote:

Have you had this issue before, or just on this shoot?

It is the first time I have noticed the problem, and I did a few tests tonight and it is still there. I am going to look back at some footage I have shot and not used yet over the past few weeks and see if it is there too. 4 frames is hard for me to spot on a small monitor unless there is a good closeup to verify lip sync. I'll see what happens

Bjorn C Hagert · September 6th, 2004, 11:20 AM

Are you using LCD or CRT monitor for viewing?

Try connecting the camera direct to a TV (with CRT) monitor and see if you still have a problem with the raw footage.

Jacques Mersereau · September 6th, 2004, 01:40 PM

I have seen problems with audio and video sync when viewing on
LCD monitors, but this sounds like the camera has a problem.

After confirming that eveything shot on it has this issue I would
send it back to Canon ;(

Valery Karyakin · May 12th, 2005, 05:33 PM

I seemed to be having a similar problem. While capturing the footage shot with XM2 through Sony DSR-25P, I could see on TV that the audio was in sync. But playing back the captured footage (both TV and LCD), the audio was visually ahead by 5 frames.

I then checked the playback frame offset (FCP HD 4.5 in system setting- not sure what this does, I couldn't find a reference in help) and the value was '4'. I set it to '0' and during the playback on the LCD screen (G4 1.5MHz) the audio visually looked in sync. However, on TV it was still ahead visually. Scratching revealed that the audio was 1 frame ahead on both TV and LCD.

I'm confused. It seems you can't test the sync by using scratch. I might end up shifting the audio at the fine cut stage so that it visually looks OK.

Jack Smith · May 12th, 2005, 08:29 PM

Chris, are you saying the original raw footage DV tape played back in the shooting camera , output composite or s cable to a NTSC monitor the audio leads the video?

Valery Karyakin · May 13th, 2005, 01:19 AM

If your question was for me then the original footage was OK and did not have any problems.

September 4th, 2004, 10:46 PM	#1
Chris Thomas Regular Crew Join Date: Jul 2004 Location: Burlington ON, Canada Posts: 118	Audio before video? I just finshed a recent edit of a 10 minute shoot, with my GL2 and a shotgun, from about 10' away from a podium, and I found that the audio was 4-5 frames ahead of the video. It did not drift, it was the same sync start to finish. I ran the original tape direct to a TV to see if it was a capture problem, but the sync was out there too... Obvoiusly easy to correct in post, but is it a common problem?

September 4th, 2004, 11:54 PM	#2
Mike Rehmus Wrangler Join Date: May 2002 Location: Vallejo, California Posts: 4,049	Sound travels much slower than light. so if anything, the audio should be 3-4 frames behind the video. Ahead doesn't 'sound' right at all. Let's play with some numbers. Assume sound travels at 700 mph. Using 'close' numbers for quicker calculations: 700 x 5000 feet (mile) = 3,500,000 feet per hour. Divide by 60 to get feet per minute = 58,333 fpm. Divide by 60 to get feet per second = 972 fps Divide by 30 to get feet per frame = 32 feet. So, using these rough numbers, for every 32 feet away from the event you set your camera, an on-camera microphone will record the audio one frame later that it actually occured. If you use a wired or wireless microphone located at the event, there is no delay of course. I think that you need to look for another answer if your audio is leading your video __________________ Mike Rehmus Hey, I can see the carrot at the end of the tunnel!

September 5th, 2004, 06:15 AM	#3
Robert J. Wolff Major Player Join Date: Sep 2001 Location: Adirondacks of New York Posts: 210	How about trying a head cleaning? Could be a small build up is your problem. Just a thought. __________________ Himself

September 5th, 2004, 08:40 AM	#4
Bryan Beasleigh Trustee Join Date: May 2002 Location: Barrie, Ontario, Canada Posts: 1,922	<<<-- Originally posted by Robert J. Wolff : How about trying a head cleaning? Could be a small build up is your problem. Just a thought. -->>> Dirty heads would cause drop outs , not a timing problem. This is a real time issue and I can't see how the camera could be at fault. __________________ Life's journey is not to arrive at the grave safely in a well preserved body, but rather to skid in sideways, totally worn out, shouting ".......holy smokin rubber lips...what a ride!"

September 5th, 2004, 08:57 AM	#5
Robert J. Wolff Major Player Join Date: Sep 2001 Location: Adirondacks of New York Posts: 210	Bryan, As I said it was just a thought. My thinking is that the video portion of the head, could be clogged enough to "lift" the tape as the video is laid down, possibly forcing audio to lay down earlier. It was just a slim chance that cleaning the head might correct the problem. If tried, and it does not correct the problem, Chris may have to take it to the camera doctor. The only other item that comes to my mind, is time-base correction has changed some how. I would be interested in hearing from Chris as to what it takes to solve the problem. __________________ Himself

September 5th, 2004, 09:50 AM	#6
Chris Thomas Regular Crew Join Date: Jul 2004 Location: Burlington ON, Canada Posts: 118	It is very strange indeed. I have had issues with the audio behind in the past, but that was when I was quite far from the source, and I realized that that is just how it works (Thanks for the ft/frame calculations Mike!).. I have not used the camera again since, so I will do a few test tonight and see if it was some type of fluke, or a problem that is still there. I guess if it exists, I will have to send my baby away :(

September 5th, 2004, 11:33 AM	#7
Mike Rehmus Wrangler Join Date: May 2002 Location: Vallejo, California Posts: 4,049	Canon, at least in their earlier cameras, didn't follow the rules with regard to handling the video/audio interleave with the result that special consideration had to be incorporated into NLEs to accomodate the issue. I've not heard of those cameras inserting the audio before the video, though. It was always a few frames after the video and in a burst so the audio could catch up. Might be interesting to post a question about audio embedding in the GL2 forum to see if anyone recognizes the problem. Just out of curiosity, you are running 16 bit audio into channels 1 & 2 and haven't somehow switched the camera to 12 bit, insert audio into channels 3 & 4? __________________ Mike Rehmus Hey, I can see the carrot at the end of the tunnel!

September 5th, 2004, 01:57 PM	#8
Jacques Mersereau Trustee Join Date: Mar 2002 Location: Ann Arbor, MI Posts: 1,334	Re: Audio before video? <<<-- Originally posted by Chris Thomas : I just finshed a recent edit of a 10 minute shoot, with my GL2 and a shotgun, from about 10' away from a podium, and I found that the audio was 4-5 frames ahead of the video. It did not drift, it was the same sync start to finish. I ran the original tape direct to a TV to see if it was a capture problem, but the sync was out there too... Obvoiusly easy to correct in post, but is it a common problem? -->>> What deck or camera are you using for playback (same one to record?)? What speakers? What monitor? If you used a shotgun, how did you get the signal into the camera? Did you record at 16bit/48Khz or 12b/32K? I don't own a GL2, but the GL series is known for mis aligned heads. Have you had this issue before, or just on this shoot? Have you ever used the shotgun on a different gig and had the same issue? __________________ Jacques Mersereau University of Michigan-Video Studio Manager

September 6th, 2004, 11:20 AM	#10
Bjorn C Hagert Regular Crew Join Date: Jul 2004 Location: Stockholm Sweden Posts: 27	Are you using LCD or CRT monitor for viewing? Try connecting the camera direct to a TV (with CRT) monitor and see if you still have a problem with the raw footage. __________________ //B C

September 6th, 2004, 01:40 PM	#11
Jacques Mersereau Trustee Join Date: Mar 2002 Location: Ann Arbor, MI Posts: 1,334	I have seen problems with audio and video sync when viewing on LCD monitors, but this sounds like the camera has a problem. After confirming that eveything shot on it has this issue I would send it back to Canon ;( __________________ Jacques Mersereau University of Michigan-Video Studio Manager

May 12th, 2005, 05:33 PM	#12
Valery Karyakin Regular Crew Join Date: Sep 2004 Location: Albania Posts: 27	I seemed to be having a similar problem. While capturing the footage shot with XM2 through Sony DSR-25P, I could see on TV that the audio was in sync. But playing back the captured footage (both TV and LCD), the audio was visually ahead by 5 frames. I then checked the playback frame offset (FCP HD 4.5 in system setting- not sure what this does, I couldn't find a reference in help) and the value was '4'. I set it to '0' and during the playback on the LCD screen (G4 1.5MHz) the audio visually looked in sync. However, on TV it was still ahead visually. Scratching revealed that the audio was 1 frame ahead on both TV and LCD. I'm confused. It seems you can't test the sync by using scratch. I might end up shifting the audio at the fine cut stage so that it visually looks OK. __________________ nle

May 12th, 2005, 08:29 PM	#13
Jack Smith Major Player Join Date: Nov 2003 Location: ontario Posts: 445	Chris, are you saying the original raw footage DV tape played back in the shooting camera , output composite or s cable to a NTSC monitor the audio leads the video?

May 13th, 2005, 01:19 AM	#14
Valery Karyakin Regular Crew Join Date: Sep 2004 Location: Albania Posts: 27	If your question was for me then the original footage was OK and did not have any problems. __________________ nle