OT: Zoom H4n Sync

kkolbo wrote on 11/28/2009, 9:08 PM

I have read a number of comments on the net about recording audio on the Zoom H4n and trying to match it up with video. They have claimed as much a one second drift at ten minutes.

I have done some testing and I can suggest that these errors are caused by operator error or poor NLE software. Either that or I have received a special unit.

I did my testing with worst case scenarios. I used a consumer pocket camcorder, the Kodak Zi8 using .h264 w/AAC LC audio. I recorded 10-15 minutes of video with sync clicks to evaluate about every minute.

Every test had the same results. I could not find even a millisecond of drift throughout the recordings when matched in Vegas. I even made another check after transcoding the video files to HDV and to .MXF.

I recorded the audio at 16bit 48K. I set the project properties in Vegas to the same.

Vegas is particularly good at handling varying sample rates etc. I suspect that the reports have come from trying to sync up in software that is not as good at audio as Vegas.

While the Zoom H4n is not the best recorder out there, it is good for its price point. For corporate and event production, I expect to be using it for collecting wild SFX and in situations where I would otherwise have to resort to wireless.

JMHO

KK

Comments

musicvid10 wrote on 11/28/2009, 9:40 PM
1) The synchronization success you report has absolutely nothing to do with "operator" or "software." It has only to do with the relative coincidence of the internal clocks of the two devices you tested, and absolutely nothing else.

2) Any two devices not connected by a wire (SMPTE Time Code) will drift. Even the most accurate time-recording devices on this planet (the cesium time clocks) are synchronized every minute to keep them together. If they weren't, . . . guess what, they would drift apart.

3) The amount of drift will vary from device to device, and second to second. This can easily be demonstrated by waveform matching of the output of two "identical" devices an exact distance from the source.

4) You are lucky. That being said, the H4n is much closer to matching a given reference frequency than its predecessor, the H4, which I own, and which drifts as much as 200ms/hr from the cams, depending on which I am able to use.

5) This is not voodoo. If you set two small boats adrift on calm seas at exactly the same time and location, will they arrive at the opposite shore at exactly the same time and location? If you connected them with a 10 ft. rope, would their chances be any better?

That is the theory behind device synchronization, when it is available. When it is not, you are literally casting your fate to the wind. Draw your own conclusions, but there is nothing inherent in operator procedure or the Vegas software that will divine the ideal result for you.

11/29/09 -- EDITED to remove statements that were offensive to the OP, with respect.

If you're really interested in this stuff, PluralEyes is your friend.
farss wrote on 11/28/2009, 10:43 PM
Crystals change frequency with temperature and age. You want accuracy think temperature controlled oven and regular calibration. Also they have quite a bit of short term drift after power up.

Some cameras used to have their 48KHz audio clocks at not exactly 48KHz by design, that never helped.

MY R-4 and MY EX1 hold very good sync. Not so my R-4 and the V1 I used to use, our HC5 is not as close to the R4 as the EX1.
Pick ten H4ns at random, it'd be interesting to see how close they all are. It's just the luck of the draw. At the price of these units you can bet they're not spending a lot of time and money calibrating crystals. Same goes for cameras.

Biggest problem I have had several times is matching a CD to a live show. Yes, it's the same CD as they played except of course maybe the director thought it was a little slow or fast and every theatre has those CD players with a speed control, sigh. Bit of a shock first time I struck this.

Bob.
Aje wrote on 11/29/2009, 5:15 AM
I agree - Plural eyes is really useful!
I just finished a reording of Brahms Ein Deutsches Requiem with
1 Zoom H4n, 1 Zoom H2, 1 Tascam HD-P2 and 3 cams.
I found an advice of Plural eyes earlier on this wonderful forum and made my first test with these recordings.
After chopping the different parts in 5 - 12 minutes long chunks and running plural eyes they were in perfect sync in barely no time.
It would have been a huge work to do it manually.
I don´t understand though why plural eyes placed the parts in wrong order on timeline - but thats a minor problem and easy to fix.
Aje


musicvid10 wrote on 11/29/2009, 6:36 AM
Aje,
Vegas PluralEyes is in beta, and there is a new version coming out soon.
Any clip it does not "recognize" it moves to the end of the track.
Best advice right now is to use the audio from one device and render to a new continuous track which becomes a reference of sorts (actual reference track capability will show up in a future beta).
The internal controls (chronological order, use markers) may help you to keep the clips in their proper order with your workflow. HTH
kkolbo wrote on 11/29/2009, 7:43 AM


Although you report no discernable drift from the combination of hardwares you used, your conclusions are totally unenlightened.

MusicVid,
I would suggest you cool your jets. Of course no independent clock based unit will retain absolute sync with another. We are talking practical application here at a corporate or lower end production (read the post). I did not suggest making a feature film or MTV submission with it. (The audio quality is not good enough for that in my opinion) Compared to the tape based analog audio recording we have used for decades the performance of this unit is acceptable. The improved H4n which I tested against multiple cameras shows no more drift than its competitors under $1,000. The posts claiming one second drift or more in 10 minutes, indicate a problem on their end. It could be operator problem, software, or a bad unit. One second is a long time in the digital world.

Operator error can be anything from not allowing for distance, reverberation, or other environmental factors such as extreme temperatures. It could be setting it for vastly different sample rates. It could also be expecting it to hold practical sync for chunks longer than 10-15 minutes. As you pointed out, using devices other than time code linked units for chunks longer that 10-15 minutes is not a professional application of the unit.

Corporate/industrial/event video lives in a world where 1/60th of a second is the target for sync. Audio production such as mixing multiple tracks from multiple mechanical sources has very different needs. Have some perspective of the context of an application.

While I respect the work of yours that I have seen, your 'holier than thou" posts do get annoying.

KK

musicvid10 wrote on 11/29/2009, 9:38 AM
I have no arguments with anything you said in your second post.
You obviously do understand the principles involved, something I did not pick up on in your first post.

1 sec/hr drift from an H4n, or even an older H4 sounds pretty radical. Of course, it is dependent on what one is syncing to, less likely the operator or the software used. I have never experienced anything close to that with the H4, but we are generally blessed with good quality cameras at our events.

I actually have one older device that drifted 8 seconds over a three hour period. After weeks of work, I completely abandoned the project for 4 years, until PluralEyes came along. Although it still entailed a lot of work, I was able to shrink the track to within one frame, then split and sync using PluralEyes, and came up with a 5.1 track from four sources that sounds marvelous. It is gratifying to be able to resurrect a project that had been pronounced DOA.

I actually planned on purchasing an H4n, until I discovered it still won't sync to free-run T/C from the cameras. Oh well, another year.

Glenmorangie and the internet are a bad combination for me.
I humbly retract my "thouness."
Cooldraft wrote on 2/11/2010, 2:47 PM
OK, this is a real problem with anyone using a digital recorder I see the problem in several forums and the suggestion if to shorten by 1%. How have you guys kept sync on long form projects using digital recorders?

EDIT/correction: They recommend shortening to 99.9% I am going to try that tonight.
musicvid10 wrote on 2/11/2010, 7:40 PM
Cooldraft,

The "99.9% Problem" is most persistently seen with 29.97 video opened in 30fps projects in Final Cut Pro. See This:

http://brucesharpe.blogspot.com/2009/06/dslr-dual-system-audio-999-solution.html

It is not a problem per se in Vegas, because timeline / rendered playback is precisely the same as your media (unless one deliberately manipulates it).

That being said, the H4n is reportedly much better with the drift issue than the original H4 (which I own), but with what drift still exists with your setup, the possible solutions are the same:

1) Time stretch / shrink in Vegas: If you precisely align waveforms visually at the beginning and end of your program, the sync will be very good, with some possible intermediate drift throughout long program segments. The biggest disadvantages are that any time manipulation introduces some quantization noise, echo, and flanging (phase differential). If your drift is only 1-2 frames per hour of material, this will likely go unnoticed.

2) This is what I do: I chop my H4 audio into ~10 minute chunks using Ctrl+S. Then I use PluralEyes to precisely align the chunks to the master track, which I have locked.
The result is perfect alignment with no artifacts whatsoever. I am careful to choose my split points exactly at zero-crossings in the quietest parts of the program. The tiny crossfades are thus indiscernible. If there are noticeable microgaps in the H4 track, I just fill them in with adjacent material. I have turned some amateur productions into cinema-quality 5.1 using this technique.

Needless to say, I am very happy with PluralEyes, and in the right hands it is an amazing tool. This is not an advertisement.

Although I went off a bit earlier in this thread, it shows just how passionate I am over this issue, and I suspect the same is true for you as well.