Fun with H4 Syncing

[David Ennis]

I have an H2 (not an H4--I misspoke above). It's 16 frames too long after an hour. That would be a highly unacceptable 2-3 frames after 10 minutes. So if I cut my track and shifted it, it would be in synch in the middle and still an unacceptable 1-2 frames off at the beginning and at the end of each segment.

So don't cut up your track--that will only make more work and give a crappy result compared to simply shrinking the whole track. Shrinking the track gives virtually perfect synch (within an unnoticeable fraction of a frame). Done.

If your program doesn't do stretching and shrinking, then maybe segmenting is your only choice. But you can get another program.

Rick, did you get a chance to try the Vegas demo to fix your track?

[Rick Thornquist]

All -

I tried Roger's procedure using Audacity and it worked! I still had the occasional crash with Audacity but had it going enough that I was able to complete the procedure (Andy, I am using the earlier version - for some reason it just crashes occasionally).

I tried the procedure with a 33 minute clip and got my magic Change Tempo - Percent Change number of 0.009. I fixed up the audio and it looks good so far. Right now I'm in the middle of processing a longer clip - crossing my fingers!

David, it looks like the stretching and shrinking procedure is going to work so I didn't try the Vegas demo. Thanks for the suggestion, though!

I was thinking... How about next time I feed the line output from the H4 into the mic input on my HV20 and record the audio with the video track? That way I can just skip all this syncing silliness and have a good audio track ready to go right away!

- Rick

[David Ennis]

Shrinking is the process that I recommended the Vegas demo for. If you got it another way, great.

[Steve House]

Originally Posted by Rick Thornquist

...
I was thinking... How about next time I feed the line output from the H4 into the mic input on my HV20 and record the audio with the video track? That way I can just skip all this syncing silliness and have a good audio track ready to go right away!

- Rick

If you're going to do that, why bother with the H4 at all? A mic preamp or mixer would be better suited. One of the reasons for going double system is to record the audio at a higher quality than possible with the in-camera audio circuitry. If you're going to ultimatly use it anyway, simplify and cut out the middle-man.

[Rick Thornquist]

Steve -

The main reason I went for the H4 was because I understood it to be a way to get good sound at a reasonable price. Getting a mic with the associated equipment is another fairly large expense that I want to avoid if possible.

I was just thinking that I could take the signal from the H4 and instead of recording it to the SD card, I could send it to the camera and have the camera record it along with the video feed. Would the audio be degraded by having it saved that way? If not, it would save me the bother of having to sync it afterwards and I wouldn't have to buy any additional equipment.

- Rick

[Steve House]

Originally Posted by Rick Thornquist

Steve -

The main reason I went for the H4 was because I understood it to be a way to get good sound at a reasonable price. Getting a mic with the associated equipment is another fairly large expense that I want to avoid if possible.

I was just thinking that I could take the signal from the H4 and instead of recording it to the SD card, I could send it to the camera and have the camera record it along with the video feed. Would the audio be degraded by having it saved that way? If not, it would save me the bother of having to sync it afterwards and I wouldn't have to buy any additional equipment.

- Rick

I can't comment on the relative quality of audio tracks recorded in the HV20 versus the H4 as I don't have hands-on experience with either one. I can only say that in general the audio on consumer cameras isn't noted for being the best in the world and your results are only going to be as good as the weakest link, which in this case I would expect to be the camera audio. So feeding a mic to the H4 but not recording it there, instead sending the signal on to the camera to record with the video would probably not give you any better results than plugging the mic directly into the camera. The H4 would be relegated to the role of an external preamp at best and any deficiencies in the camera audio would still be in play. Another issue to be aware of is the need to match levels - I believe the HV20 only has a mic-level input while you'd be coming out of the H4 at line level and its output would be much too hot for the camera input. Overloading the camera's inputs could actually make it sound worse.

[Bill Rankin]

I just recorded an hour and 7 minute presentation to sync with the video. My H4, just purchased from BH, is fast by about 1.87 seconds over that time frame.

It's a hassle to cut and resync, but it does have the XLR's which is handy and the quality of the recording good. Meaning no hum, clicks, etc. Although, the recording level was very low. I recorded from a line out of the wireless station using 1/8 plug and adapted to my two xlrs. Very low on the meters and I had to amplify significantly in Audition.

It's doable for the price, I suppose.

CORRECTION: The H4 recording is SLOWER by 1.87 seconds, not faster.

Also, shrinking works perfectly instead of cut and sync. I went from 100 to 100.05 and it lined up perfectly.

[Roger Shore]

Originally Posted by Bill Rankin

Also, shrinking works perfectly instead of cut and sync. I went from 100 to 100.05 and it lined up perfectly.

I've got to agree with you there Bill - although I linked to a procedure I devised using free programs, I find it even easier to do, as you do, using Audition (or in my case, CoolEditPro2).
I firmly believe the the audio sync problem is nearly always a result of the difference in device clock frequencies, rather than the 'drift' of any individual device.
It may well be that the camera clock is the one that's at fault, but as it is the one that is intrinsically linked to the audio, then the remote recording device has the audio that has to be shrunk (or stretched!). And if you know in advance by how much, then it really becomes a much simpler task.
Definitely easier than doing it in small 'chunks', IMHO.

Of course, we should all really use synced timecode, but in the real world, where budgets are sometimes tight?......

[Steve House]

Originally Posted by Roger Shore

...
Of course, we should all really use synced timecode, but in the real world, where budgets are sometimes tight?......

Just FYI - it's a common belief that synced timecode alone will keep the two devices in sync but it's not correct. Timecode is like a slate and recording identical code with the video and the audio lets you pick any arbitrary point in the video timeline and align the matching point in the audio timeline to it. But timecode doesn't control the recording or playback SPEED of either recording and if their clocks aren't running at exactly the same rate when making the the recording their lengths will be different - if you align the codes at the start of the file you'll find they're out of alignment at the end, if you line up in the middle of the file you'll both the head and tail will be off, etc. With film and analog recording or a DAT that's going through telecine it's another story because the timecode recorded on the audio tape or file controlls the speed of the playback device that resolved magnetic tape to perforated magnetic film or the speed of the telecine transfer. Sound for video with file-based digital recording is a whole different process. To get the video and audio to stay in "sync" over the duration of a shot, the video sample clock in the camera and the audio sample clock in the recorder must be slaved one to the other or to a common source clock, using genlock I/O on the camera with wordclock I/O on the recorder or deriving wordclock for the audio from the video blackburst on the camera. That makes sure that the audio and video files are exactly the same length when loaded into the NLE. Then you can couple that with timecode to aid in establishing the initial lineup of the two files and you're in business.

The way big0time multicam shoots manage it is they have a master "house clock" that generates timecode, video sync, and wordclock. TC plus video sync goes to all the cameras and TC plus wordclock goes to the audio gear. That's where "Lockit boxes" come in - they're tuned to the master clock and then attached to the various devices to provide identical clocks to all of them without requiring hard-wired cabling. Now everything has common TC and a common clock reference.

[David Ennis]

I've never quite understood the fuss about timecode synching for audio with video. If you have a very large number of tracks, I can understand the desire to avoid having to make a lot of adjustments in post.

But when I have three camera tracks from a multicam shoot, plus a few additional imported audio tracks (house mixer, my own orchestra pit recording, etc.), what's the big deal? It's going to be an 80+ hour editing project anyway, so a half-hour or so of that is aligning audio tracks. Not bad.

The resulting synch is as good as I think I see and hear at the movies or on TV. Am I wrong? So other than the occasional studio pro, what are people on this board doing that makes them obsess about this?