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Old November 14th, 2006, 11:27 PM   #1
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audio for multi camera shoot

I hope this is the right forum to ask this question. We have been shooting an event every year with multiple cameras and one thing that is always an issue during post is the audio.

The sound is actually coming into a sound board so I was looking for the best (inexpensive) way to get a master audio track recorded (preferably straight to a HD).

Last year we used one of the DVX100s as the master audio (xlr from sound board to camera), however, that was still cumbersome as the event is long and required a lot of tape changes, not to mention it hindered camera placement.

Initially, I was thinking about getting an ikey or ikey plus (http://www.ikey-audio.com/ikeyplus.htm) and capturing the sound separately. However, it seems that someone that knows a lot about audio may have a better/more cost effective solution. Using a device to go from the sound board to a laptop with an external USB harddrive could be an option too.

Any suggestions would be much appreciated.

Also, is there an efficient way to "mark" all the cameras with some sort of audio spike that is inaudible to the human ear but that would show up in the NLE. It seems that would speed up syncing the cameras if there was something like that which could be fired off every time one of the cameras did a tape change.
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Old November 14th, 2006, 11:53 PM   #2
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You aren't live switching this event?

If not, why not?
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Old November 14th, 2006, 11:58 PM   #3
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what if you just did a free-run timecode?
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Old November 15th, 2006, 12:08 AM   #4
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I've noticed the iKey havn't got a XRL input,

Are you mic using XRL cable?
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Old November 21st, 2006, 05:40 PM   #5
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Wade,
We have always just recorded with 3 cameras and done all the capturing and editing in post.

Wade,
I still need master audio recording device.

SiuChung,
We have XLR capability coming from a sound board.
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Old November 21st, 2006, 07:51 PM   #6
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live sound

heres an idea....send XLR feed to a USB device with XLR inputs, like a Zoom H4, or a Firepod, or an Alesis IO, then just live capture with Vegas or some other NLE right to an external drive.....I have captured live with Vegas and it will just roll - record until the drive is full (200 gigs or so should give you HOURS of recording time)....I never tried to capture just audio, but I dont see why that would be a problem, just create a track and hit the record button...or, just capture with Sound Forge...be sure to do a hand clap or use some sort of slate at the begining so you can easiliy find synch in post....
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Old November 21st, 2006, 08:03 PM   #7
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On live shoots I usually do of concerts and things, audio is captured to a Protools system...

In your case, that is a good suggestion to an XLR to USB interface to capture audio right to the hard drive.

For sync, run the shotgun mic on each camera....sync up all the cameras in your timeline, then sync up your clean audio to that. Delete the dirty audio from the cameras...voila - you're synced.
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Old November 21st, 2006, 08:24 PM   #8
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Hi Brian,
Capturing audio direct to your NLE is a great idea. Some usb/firewire interfaces to consider are M-Audio's Firewire410/Mobilepre/Fastrackpro , Presonus Firepod/Firebox , MOTU Traveller, Tapco usblink.
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Old November 24th, 2006, 08:42 AM   #9
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Hi Brian,

Just something else to throw into the mix (and hopefully save you some time in the long run):

There is a potential problem when using multiple cameras and a single master audio track captured using some or the other external audio capture device.

Here is a link to a thread that I started some time ago:

http://www.dvinfo.net/conf/showthread.php?t=64559

I just read it know for the first time in a couple of months and I am quite impressed with the amount of testing I did at the time and the amount of technical information it contains that was furnished by fellow dvinfo users.

Basically there is an inherent problem when using multiple devices to capture video and audio seperately and then synching the whole lot together in post.

The thread appears to wander around a little but press on (even if you get bored). There is a lot of technical information in this thread that may save you weeks of frustration.

Although after rereading your initial post it seems that you have probably already come across this problem and either live with it or have found a solution that I could not in which case YOUR input would be appreciated.

Anyway - I see that there are a couple of relatively new posts regarding audio and video synch problems appearing so this will at least put my thread back in the spotlight and maybe save some people from pulling their hair out (or worse).

Regards,

Dale Paterson.
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Old November 24th, 2006, 07:51 PM   #10
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Sync!!

Hi Dale

You all seem to be hitting the target all around the "Bull's Eye" but just off.

The problem is the clocks not just the time code. What is needed is a way to lock the clock of the digital audio system to the clock of the Master Camera.

(I would use one camera on a wide shot as the Master Camera and if I could lock the clocks of all the other cameras to that but that will not be posible with the cameras in use. The least expenceive camers that I know of that will "Genlock to external sync are the Canon XL-H1 and the XH-G1)

Take a video out of the the Master Camera and use that as the reference for the clock in the audio chain. I hope the mixer, which is the device doing the audio A/D, can lock to an external video signal. That could be the a straight video signal or just the "Black Burst" portion of that signal. I.E. striping all the picture information off and leaving just the sync pulses.

I that high priced production facility they were locking the cameras and any audio A/Ds to house sync or black burst.

Hope this helps.

Grayson

Last edited by Douglas Spotted Eagle; November 24th, 2006 at 08:26 PM. Reason: Please do not cross post.
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Old November 24th, 2006, 08:36 PM   #11
 
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Grayson;
Given a DVX and an iKey, or MiniDisc player, or similar device, how would you lock off the audio from the video master to the external, separate audio device?
I'm curious to know how you'd accomplish this.
It's very important to be aware of what tools the original poster has available.
Your last sentence:
Quote:
I that high priced production facility they were locking the cameras and any audio A/Ds to house sync or black burst.
has me a little confused?
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Old November 25th, 2006, 12:29 AM   #12
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Good Morning,

Grayson - thanks for the response. After all my frustration and testing I realise that it is the device clocks and not a timecode issue.

Douglas is right - it does depend on the equipment that you have i.e. prosumer or professional.

Having said that even being able to synch one camera (the master) using genlock for example to the external audio capture device would still not solve the problem i.e. the other cameras would still be doing their own thing. The only way that this can work is if all devices are genlocked to each other.

Put it this way - using only one camera (without genlock) you could take a master audio out from the mixer (or whatever audio capture device) to the master camera and the audio on this camera would be in synch with the video on the tape in this camera BUT the other cameras would still be / go out because of their individual clocks.

Anyway - let me just say - it was not my intention to hijack Brian's thread - I just thought that it was something that he should be aware of (if he was not aware of it already). This topic I have beaten to death in my own thread and to date have not found a solution other than using reference tones at the beginning and end each cameras tape or using clapper boards and manually aligning the audio in post (I use Vegas). How's that for hitech!

On the other hand if anyone has come up with a REAL hitech solution for solving this problem using equipment that does not have genlock then by all means your solution would be more than welcomed.

Regards,

Dale.
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Old November 25th, 2006, 12:41 AM   #13
 
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Dale, since you're using Vegas, it's exceptionally easy to bring the cams to sync'd audio, it just takes a few seconds, particularly on a multicam shoot. We're doing more and more in HDV these days, and less and less in Beta, in fact, almost nothing. So, nothing is locked. Long and short form media all falls nicely into place, as even over long form, you're at worst off by a few frames after an hour, and as you've figured out in Vegas, they sync fast. You've just gotta be sure the audio is all at the same sample rate, same bitrate. If it's not, then between the differing clocks and sample rate, it's a lot of cutting.
I start by putting all cams on the timeline with my master audio enabled, and all cam audio muted excepting one. I loop a small section that contains a percussive, and you'll know immediately which way you need to go. Disable "sync to frames" in Vegas so you can nudge audio in samples rather than in frames or half frames. Doing this while looping will allow you to immediately hear whether you're in or not. If you hear chorusing, echoing, flanging, or any other "ing" then you're not in sync. It should be invisible, except for a volume drop when you mute either the master or wild audio track.
Once one track is sync'd, then mute it and move on. Of course, VASST has syncing tools that can do this for you, too, but frankly, I find the method I've been using for a few years to be more intuitive for me.
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Old November 25th, 2006, 02:42 AM   #14
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Hello.

That is the only way to do it.

For my tests it was easy. I started three cameras and the external recorder in close proximity to each other and recorded (generated) five pager type beeps and then just toward the end of the hour (tape) recorded (generated) another five beeps. When all of the tracks were on the timeline it was a cinch to get them all in synch BUT in a live situation you just have to hope that somebody coughs or claps their hands or accidentally hits the mic stand at the beginning and near the end of each hour so that you have your percussive reference points!!! Using voice or music and listening for that flanging sound is not exactly an exact science particularly when you have four devices running each with there own agenda!!!

What is needed is either:

Some sort of device that transmits a clock or timing signal or something like that and receivers that can be plugged into our FX1's/Z1's or any other make of prosumer camcorder via LANC or something like that to ensure synch of all of these devices (and you would need an audio capture device that could work off of these receivers as well). I don't think that any of the prosumer cameras gives you the choice of whether or not to use an internal or external clock though.

or

'Capture' software (Douglas - I know you don't like the word 'capture' - see below) that somehow uses the internal clock of the PC being used for 'capture' as a reference and resamples everything that is 'captured' from any source on the fly i.e. as it is being 'captured'. That could solve the problem and would be an elegant solution. This would be different from 'copying' the DV file on the tape in the camcorder to the PC which is actually what we are all doing (see - I know the difference).

I know that over an hour there is only a small margin of error but it makes a huge difference at the end of each hour especially when you have five tracks on the timeline and remember that you are also (in my case) dealing with the timing difference caused between the difference between the speed of sound and the speed of light i.e. the difference between the distance of the subject to the 'master' camera and the distance between the subject and the mic that goes to the mixer i.e. the camera might be thirty metres away from the subject but the mic is not more than a couple of centimetres away from the subject.

Then there is also the problem of Vegas previews being slightly out of synch with the audio anyway (unless you preview with 'Print to Tape') so even attempting to synch visually is impossible.

The fact that this issue still exists in this modern day and age still amuses me though. Forget about audio sample rates and the like etc. etc. etc. Logically 25fps should equal 25fps should equal 25fps (get the picture) and the audio should follow but 25fps might average 24.999fps over an hour on one device and 25.001fps over an hour on another device and there is your difference (this is making my brain go fuzzy again).

Basically it is a pain but just think how boring it would be if everything just worked!!!

Regards,

Dale.
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Old November 25th, 2006, 05:17 AM   #15
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I do quite a lot of multi-camera shoots of live music events - the system I use is to record stereo audio onto my main camera - and if I can, the same feed to at least one other. The others record room sound - it actually is quite useful for adding 'crowd noise'.

You can do a sync point at various times if you want to, but there is always a small amount of drift in a long continuous shot.

I use premiere pro to edit, using the multicam feature which for me works very well. However, I tend to edit a song at a time, so that any render issues don't suddenly mean having to go away while 4 60 min sequences sort themselves out.

My sync is usually quite simple - lots of little tricks, like the drummer being the clapper board, lighting effects that can be used as the sync point, and the audio tracks themselves. It's quite simple to zoom in on the audio waveforms and slip the tracks until the waveforms match. This system works really well. I think sync is often overstated, and really complicated timecode sync isn't required. Lip sync is the obvious aim, and getting it right isn't that difficult.
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