looking for a iriver replacement

[Steve House]

It perplexes me that you guys don't see drifting when most who do mainly broadcast concerts, episodics, or theatrical features do. What is different? The only thing I can some up with off-hand is most of your shots might be long shots where it's relatively difficult to see the subject's precise lip movements in detail so it takes a very gross loss of sync for it to be visible on the screen. OTOH, if you were shooting closeups where the person speaking's face fills the screen and you can match a sound to the lip motion you might see more of an issue.

[Garrett Low]

For Bill and Noa, where are your cameras placed relative to the recorder/mic (if you have a lav connected to the small recorder in the grooms pocket)?

I do have to say that my experience with the Zoom H4n was not like yours. When I tried one out I found that after only 10 minutes there was a noticeable shift. I have a Sony D50 that goes 2+ frames per hour out of synch and that is very consistent. Used on several long plays and recitals. That's a bout the best I've been able to find without using Genlock.

Garrett

[Noa Put]

Well, I promised not to say anything anymore but as long people don't start to call me "Mr" I"m willing to give a serious answer.

About the way I sync audio tracks, I never do that by looking at the persons mouth, I always do it by looking at the waveform and first look at a obvious peak in the sound in the beginning that I can find back in all my audio tracks, I use my xh-a1 as master to sync all the rest of the audio with. The second check is by listening, I playback 2 tracks and make then sound equally loud, if there is a deviation, you will hear that in the beginning, unless your deaf and I repeat the same at the end of the recordings. If the waveform peaks still match and if I couldn't hear any echo in the sound all is good to me. With echo I mean that what you hear if the audio on one tracks is slightly off, the further it's off the bigger the echo gets. I"m sure that's a routine many other wedding videographers use and they also might use pluraleyes for easier syncing.

[Noa Put]

Originally Posted by Garrett Low

I do have to say that my experience with the Zoom H4n was not like yours.

I didn't say my zoom h4 could hold sync, it doesn't, it goes quite a lot out of sync and I have to correct that in audacity. It is a first gen recorder from zoom and all those where known for not holding sync, a problem even the manufacturer has acknowledged, then it seems that the newer version suffers the same problem.

[Bill Grant]

I synch mine by pluraleyes. I use DSLRs now along with a HMC150. So the closeups are all short clips, but when I was using the Canon A1, I would consistently have 1 hr clips that kept synch fine with irivers. Maybe the science and stuff is important on broadcast and so on, or maybe it's because they've never tried it any other way :)
Bill

[Steve House]

Originally Posted by Noa Put

..
About the way I sync audio tracks, I never do that by looking at the persons mouth, I always do it by looking at the waveform and first look at a obvious peak in the sound in the beginning that I can find back in all my audio tracks, I use my xh-a1 as master to sync all the rest of the audio with. ...

Are you looking at a true impulse noise, like clapper sticks banging together or even a handclap, in the camera audio track as you head-end sync point?

[Noa Put]

Well, in my tests I clapped my hands but I don't do that in church, an obvious sound peak could come from sliding my Canon into my manfrotto tripodhead, it makes a distinct clicking sound once the safety pin moves into place which is easily seen in the waveform on all recorders. I don't listen to the sound untill I hear that clicking sound, on my xh-a1 waveform those peaks are easily to be found as the clicking sound appears closest to the camera's microphone.

[Steve House]

Originally Posted by Noa Put

Well, in my tests I clapped my hands but I don't do that in church, an obvious sound peak could come from sliding my Canon into my manfrotto tripodhead, it makes a distinct clicking sound once the safety pin moves into place which is easily seen in the waveform on all recorders. I don't listen to the sound untill I hear that clicking sound, on my xh-a1 waveform those peaks are easily to be found as the clicking sound appears closest to the camera's microphone.

So you're saying that both the sound recorder in the groom's pocket and the camera are rolling when you attach the camera into the tripod mount and the 'click' of the mount's pin is clearly audible on both the camera audio (which I'd expect) AND on the audio track from the groom's lav & recorder (surprising)?

[Noa Put]

Yes, it could be depending how close I am standing to the groom, but like I said, it can be any peak sound, that might be even louder, it doesn't necessarily have to be the tripod head clicking sound.

[Noa Put]

Maybe I have to clarify my statement of not looking at a persons mouth to synchronisize, I don't look at persons speaking to sync the sound with their mouthmovements but I just will pick a part where I hear the first person speak and I will find that part in all my audio recorders, then I do some rough synching up based on what I hear again and then I look at the waveform to find obvious peaksound and once I found that I"ll synch precisely on that peak and verify again just by listening. I always use my xh-a1 as a "base" and sync all other recorders on that, I make them sound equally loud so I will hear out off sync issues immediately. Then I check again at the end and just listen to each track separately with my xh-a1 recording running along as a base audio track, if there is drifting in audio I will hear it, I use my waveform again just to verify and look for obvious peaks to compare.

[Greg Miller]

Noa,

It sounds as if you have given a lot of thought to evolving your "sync test" procedure. Assuming that you are zooming in to the frame level (and I believe you have confirmed that in an earlier post), then I see nothing wrong with the procedure and I tend to trust your conclusions.

So perhaps you are indeed blessed with an unusually copacetic batch of equipment... the audio gods have smiled upon you!

One thing I have often wondered in the past, when people are discussing sync drift, is this: Which is really drifting? The camera, or the audio recorder? I'm not sure whether anyone has actually tested for that. Maybe audio recorders are really stable, and the cameras account for most of the drift. (I tend to doubt that, since cameras should have pretty complex and accurate time bases... but I don't know for certain.)

One could, for example, record an hour from a known time source (such as the WWV time broadcasts here in the USA). Then upon playback, carefully sync a "beep" at the beginning of the track with the current broadcast, and compare the two sets of beeps (recorded beeps, and live beeps) during the course of the hour-long playback.

A similar test could be made with the video, by filming a running time code display, then comparing upon playback.

Of course human reflex time would enter into the above tests, so it would not be simple to perform them accurately.

Just speculating here, but thought I'd throw out this little nagging thought at the back of my brain. Maybe someone has conducted more detailed tests, or knows more about the innards of the equipment (especially the camera time bases).

[Noa Put]

For these type of questions I usually look at National Geographic :) I also wonder then why videocamera's, small and bigger, different brands, shooting to different formats mixed in multi-cam shoot stay synced all the way. I have done a 4 multicam shoots before in those circumstances without an issue, is it so that just because they are camera's we should not question their ability to hold sync while with audio recorders you should?

[Steve House]

Because of the need to synchronize all the various elements in the broadcast chain from original camera through to final monitor, the tolerances for camera sample rate clocks are tighter than is the case for low-cost audio recorders. If a camera runs even a fraction of a percent off of the nominal sample rate the picture gets scrambled. But consider the case of an audio recorder that is 1% too low. It is supposed to be at 48,000 samples per second but it's only running at 47,520. If you record exactly 1 minute of audio it should contain 2880000 samples but if fact it will only contain 2851200. When you then play it back ON THE SAME RECORDER, as is usually the case in the applications these recorders are intended to fill, it will use the same slow sample clock to control the playback duration and those 2851200 will play back in exactly 1 minute. But now put that same file in a playback device that is running at the proper 48000 samples per second. When it plays the 2851200 samples it has to work with in this file, only 2851200/2880000 of a minute will have elapsed - what SHOULD be playing in 60 seconds as far as the original recorder is concerned actually plays in 59.4 seconds. At 25 FPS (since Noa is in PAL-land), that 0.6 seconds amounts to 15 frames of "drift" in only 1 minute of recording. Luckily even the cheapest audio clock circuits are better than that. But it doesn't take much to take it far enough off of nominal to get a few frames fast or slow in, say, 10 minutes. It turns out that the NLE's we all use are based on the assumption that the camera is God when it comes to sync and their sample clocks are running at EXACTLY 48000 SPS (samples per second) - everything else has to conform to the clock embedded in the video file. Even if the camera was slightly off, not enough to scramble the image but still off, there would be no detectable change in the image - motion would be a little faster or slower than it was in the original scene but we'd never notice it. But if a separate audio recorder is even the slightest bit different from the 48kHz the standard calls for, the timing on the audio file will gradually diverge from that of the video file when they are married together under the same sample rate clock in the NLE timeline. One hour of PAL video has 90,000 frames. To maintain frame level accuracy over that hour, your audio recorder's clock can only deviate from the camera's by no more than 0.00011% - do'able but it takes some sound engineering and very tight production testing and QA monitoring and those don't come cheap. It's that engineering and QA that makes a Lockit box, which is essentially ONLY a highly accurate clock circuit, cost in the neighborhood of a thousand bucks US.

[Noa Put]

Something tells that you are involved in some kind of audio production every day :D
Thx for the clarification, it's too complicated for me though, I"ll just continue looking at my waveforms. :)

[Bill Grant]

I was gonna say, if we gotta work this hard to break it... it probably ain't broke. :-)
Bill