Fun with H4 Syncing
 

All right - I think I'm a pretty smart guy, but after banging my head against a wall for weeks on this I admit defeat. I simply can't get an H4 wav file to sync up with the video that I shot.

I recorded an interview that's about an hour long. I recorded the sound on both the H4 and the camera's internal mic and imported both into Premiere CS3. I thought that I would just adjust the Speed/Duration of the H4 file and line up the waveforms. The only problem is that no matter what number I use for the Speed/Duration, they never line up throughout the interview.

I've searched for and read tons of information online and tried a preposterous number of things but still can't get it to work.

Does somebody have a method of doing this syncing in Premiere?

- Rick

I don't know Premier's tools. but if you're desperate to fix this particular footage you can download the trial version of Vegas. Its time stretch function works fine with my long (one hour +) H4 files.

there is NO reason to change the speed of the audio. thats why you have a problem. this isn't the days of film where 24fps was telecine'd to NTSC and so became 23.976. if you shot with a video camera, even at 24P, 60 sec on tape = 60 sec on audio HD, nothing more, nothing less.

if the camera or HD recorder dropped out of sync because one of them stopped started, simply use a divide by 2 comparison to find the break point. it works like this if the front is ok, go to the middle and check. if its bad there, go 1/2 from there back and check. if its good, go 1/2 from the current to last check point and check. if its bad, go 1/2 way back. this should require about 7 tries to find the bad spot within a minute or two on a long take.

Without slaving the recorder to the camera (which you can't do with the H4), you can't expect if to stay in sync. However as a past owner of the Zoom crap from (we know where), they are all over the board on clock speed. Hard to do any consistent time stretch....

Very true, But recording sample clocks can be off-spec, especially with consumer gear. Let's say he recorded 60 minutes (3600 seconds) of material with the H4 at a nominal 48kHz but the recorder's clock was really 0.1% slow. One hour's worth of material should have exactly 172,800,000 samples but because of the slow clock it only has 172,627,200 samples. Now that material is loaded into an NLE that is exactly on 48kHz. At the correct sample rate those 172,627,200 samples that were recorded in 60 minutes will play out in 59 minutes 24 seconds. Since the camera can be assumed to be the master, sync lined up at the start of the shot will drift out by 36 seconds at the end with H4 sound leading camera sound.

The OP didn't say what camera he was using but another issue that could be the culprit is the fact that miniDV audio isn't locked to picture and the video and audio sample clocks in the camera itself could be slightly off from each other. They'll be in sync when played from the camera but drift out when played in the NLE. If this happend to him, it could be the reference tracks recorded in camera are slightly off with respect to picture after capture. Trying to lineup the H4 to them would mean he's trying to hit a moving target. I've seen several references that recommend when capturing very long shots one take the video through Firewire but to take the camera audio through an analog interface so they're resampled to avoid the problem of drift between them

There's no substitute for proper slates and for long takes I think getting both a head slate and a tail slate when possible is a really good idea.

I use the technique I outlined here: http://www.mfbb.net/myvideoproblems/...s-about25.html.
to resync externally recorded audio, when the professional options are not available.
Bit long winded the first time, and of course it may be easily adapted to suit whichever audio editor you have, but should only need to be done once for each recorder.

David -

Good idea! I've downloaded Vegas and will give it a try.

Steve Oakley -

There were no dropouts. As Steve House explained, with the H4, 60 seconds on tape doesn't necessarily equal 60 seconds on audio.

Steve House -

I recorded the video using a Canon HV20. The camera was connected to a Blackmagic Intensity Pro via HDMI and I recorded the video uncompressed. The audio that was was recorded via the camera is synced up with the video - no problem there. I also did slate the take but even with the slates I'm still having problems.

Roger -

I did find and try your technique, but couldn't get Audacity to work. It kept crashing whenever I loaded one of the sound files. Other programs, like Premiere, load the files but Audacity just doesn't like them. I'll be trying some other audio programs as well.

Thanks for the suggestions - I'll try them. Hopefully I'll get this thing to work!

- Rick

all I can say is starting in the 80's shooting 16 & a Nagra, this wasn't a problem.there was certainly no cable between camera and tape. yes you did have a slight speed change due to telecine, but that was a known factor once done, all was good. If the H4 doesn't have a stable on time clock, why use it ? I'd make who ever sold this to you take it back as defective product.

a couple of years ago I ran a DVCpro 450 deck to record a board feed from a show basically using it as a 2hr 48k 16bit recorder. ran 4hrs thru the deck. locked seemlessly to the 3 cams shooting. deck was self referenced. cameras where 300ft away from the recorder with no connection of any sort. there are plenty of accurately timed recorders out there. I was interested in one of these low end recorders, but if they don't have good clocks, it really defeats the purpose of using it and being untethered from the camera.

in your case there is but one somewhat easy fix. play thru it and every time it starts to drift noticibly, cut the audio track ( ideally between sentences or pauses, patch gap with room tone ) and move it + or - a frame so it locks again. repeat until end.I've seen this done many times. if the h4 varies its clock, this is the only fix. if you have access to pro tools and the ADR pluging they make for this, it would pretty much be automated.

Audacity
 

I find Audacity rock steady and very easy to use/very useful - it will be ideal in what you're trying to do (I have a Zoom H2 so know the issue you're talking about well!). Did you download the new beta version maybe? - if so I suggest you try the earlier version (both on this link.)

Also, just seen Steve's reply and yes I sometimes do that too - cutting the sound file up into smaller, easier to manage segments works well in Vegas 7e and Ulead VS10+. I find syncing audio this way VERY easy to do.

http://audacity.sourceforge.net/

Clock stability is certainly one of the things that accounts for the price difference between a ~$400 recorder like the Zoom and a ~$2500 professional recorder like the SD702/702t. But even Sound Devices cautions that drift may occur on shots running over about 15 minutes in duration because some cameras might not be spot on.

I don't find the H4's clock to be unstable, it just runs fast resulting in an audio track that's too long. So I shrink it. A lot has been posted about it.

Problem is, once you download the video from your camera into the NLE, then it (and it's onboard 'sync' audio) become the master track, so even if your remote audio recorder has a more accurate clock than your camera, it's the recorder track length you'd have to change!

Yep, you're exactly right.

Strictly speaking I shouldn't have used the term "unstable." "Inaccurate" would be more correct. To hold sync, the camera clock and the recorder clock must be exactly the same, whether that's exactly 48kHz or not.

How about cutting the audio file into shorter segments, and line them each up separately? You should not have so much drift in, say, 10 minutes.
Patrick