Audio Sync

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    • #41225
      AvatarTEd
      Participant

      After reading the review this month, I purchased the Zoom H4 Digital recorder. I enjoy recording our school band concerts, plays etc, and though that moving the recorder closer to the action would subtantially improve my video quality.

      The H4 works great – very much improved quality from Camera. πŸ˜›

      I had assumed that because the recorder is digital, as is my camera (older Digital 8 system), that the two files should sync nicely. Unfortunately their is about a 6 second bust after 30 minutes. 😑 I had to "stretch" my video, in order to match it with the audio. Is this normal? I plan to do a test with a watch over 15-20 minutes to see if it is the camera, or H4, or both that are out of sync.

      I can see where a "clapper" would be very handy at the start (and apparently also at the end) of a sceen. Unfortunately this is not always possible…..

      Any advise?
      πŸ˜•
      Thanks

    • #175376
      AvatarAnonymous
      Guest

      Hi Ted,

      I would start by testing results between your recording format. My feeling is that if you’re using mp3 as a recording format you will experience such problems. You might get better results in WAV format, however, there’s no guarantee. I think the root issue is that the device does not have the same time-base format as video. That means the device will interpret time differently. In your case the H4 compresses the time. It’s only noticeable when you’re recording for longer durations.

      As for compensating for that time compression, you’re technique of slowing down the video fractionally makes perfect sense. Although, I think that could be damaging to the quality of the video so I’ll suggest another idea. If you can find a few places (say every 8-10 minutes) in your video where there’s a lull or a similar audio environment (such as an applause or silence), cut the audio in those places and then slide each section and align them to fit naturally with the video. Then fill in the gaps with some selections from that audio file the imitate the audio environment of that particular scene. Make sure to mix it in using you volume/gain controls so that it sounds natural.

      Another technique is to stretch the audio and adjust the pitch to compensate for the slow down. This in many ways can be easier to pull off than my first suggestion. But, you’ll need the right software/audio filter effects to do it. What do you have at your disposal?

      Mark

    • #175377
      AvatarTEd
      Participant

      Thanks Hank and Mark for the suggestions.

      I made a short 12 min movie last night as a trial, but ran out of time before I had a chance to load it on the computer and put the video and wave files side by side. I used a stop watch, and clapped my hands at various time intervals. I should be able to see which component is different.

      Mark – I think you may be on to something with the recording format. I used the MP3 format on the H4 Digital recorder. Today before work, I loaded the mp3 file into an audio program, and saved it as a wav file. This file matched the video much more closely, althouth not perfectly. I have a feeling that if I had used the wav format on the original recording, it would have worked better. I will do another test and let you know. I hope to have some time this weekend.

      I hadn’t thought about the reduction in video quality by changing slowing it down or speeding it up slightly, but it makes sense. I do have some software that will let me do it with the audio – so that may work better. I suspect that with the very minimal change (2-3 seconds over 30 minutes – 0.2%) it should not change the pitch noticably – particularly when there is no music in this particular project. The idea of chopping out little bits of audio is also interesting. I’ll give it a try and let you know how I make out.

      Thanks again.

    • #175378
      AvatarTEd
      Participant

      My trials continue to show a slight time sync difference between the digital recorder and my digital 8 camcorder.
      The camera appears to be very accurate – at least camparing the timestamp and a stopwatch.
      In each case my Audio is a bit longer than the video.
      I took your advise can cut small sections of the audio out. This was some trouble but worked very well.
      I removed two frames every minute. I was able to target relatively silent spots in the audio – so it is not noticable.

      The effect seems to be consistent with each new recording. Still not sure if it is my software, the recorder or the cam…
      At least I have a workaround…

      Thanks again.

    • #175379
      Avatarcwillsher
      Participant

      Have you tried recording with the H4 set at different sample rates as well? The difference between 44.1Khz and 48Khz recordings may not always be immediately (audibly) apparent but if you import a 44.1Khz file into a 48Khz video project there will be a noticeable difference in the duration of the files.

      I have an H4 here but haven’t had a chance to try it on a video project yet, I’ve just been sound-collecting so far. I would be interested in knowing more details regarding your tests.

      Good luck!

      Colin

    • #175380
      AvatarTEd
      Participant

      Colin

      I just got my H4 for I am working on my first project – which was a 3 act school play. Each act was about 30 minutes long.

      I had assumed that the audio sync would be a no-brainer. I was supprised when I found that by the end of each act (30 minutes) the audio and video were out of sync. I originally recorded in mp3 format – and the audio was out by about 3 seconds at the end of 30 minutes. Based on the advice above, I converted the audio to wav. It was then much closer, but still about 1/2 second out after 30 minutes – very noticable.

      As above, I solved the issue by cutting out 2 frame segments of the audio every minute or so of the video. Some hassle, but it saved the project and worked very well.

      I did a test by setting up my video camera in the kitchen and running it along side the H4 and a stopwatch for 15 minutes. I tried both mp3 format and wav as recording format. I did not try different sample rates, but maybe should.

      I then loaded the audio and video files into my ULEAD 10 editing program.
      The timecode on the camera matched the stopwatch exactly (as close as I could tell). I made a clapping sound at the start and end of the test. In each test the sound file did not match up with the video. In each case it was about 1/2 second longer than the corresponding video. When I get a chance, I will muc with the sample rates to see if that makes a difference – both on the H4 and the Editing software..

      It would be much simpler if the audio and video would sync without all of the extra work…

      Thanks

      Ted

    • #175381
      Avatarcwillsher
      Participant

      I haven’t worked it out but I would imagine playing a 44.1Khz audio file in 48K video project would generate a much more significant difference than 1 second per hour. This is complete guesswork on my part but it could be that your edit software is perhaps converting your 44.1K file to 48K – either on the fly or when it is imported and so it could feasibly be this conversion that is slightly awry over the long duration. As I say, this is complete speculation on my part but WAV tests at both 44.1 & 48 may reveal something.

      Just a thought. But in any case, certainly don’t record in mp3 format when you need a/v sync.

      C

    • #175382
      Avatarcwillsher
      Participant

      My point Hank is that the software could have been playing back the audio at a different sample rate than it was recorded at. Admittedly most software can handle multiple sample rates within a single project but a test I did with Logic Pro goes someway to explaining my theory. I recorded a one minute segment at 48Khz and then switched the projects sample rate to 44.1Khz – 5 seconds were added to the files duration in the timeline due to the fact that it was taking longer to playback all the samples.

      But that’s not really my point anyway. I’m not familiar with the Ulead software and just figured that maybe, just maybe sample rate conversion could be an issue if there are recordings with multiple sample rates in the same project – I couldn’t get Final Cut Pro to hiccup with a quick test with short files but you just never know. Just trying to help.

      C

    • #175383
      Avatarcwillsher
      Participant

      I agree, the fact that the discrepancy is so small points to the fact that the playback sample rate is not the issue, so we may have gone a bit OT here but it is a fact that if you playback a file with a different sample rate to the one it was recorded there will be pitch and time changes in playback. I think most video software handles this in the background so we don’t have to think about it and it’s this process that I was questioning. This Wiki article touches on the subject:
      Sample Rate Conversion

      Perhaps it’s more likely that the difference is simply down to the fact that one recording was made on a mechanical, tape-based device and the other on solid-state media.

      C

    • #175384
      AvatarTEd
      Participant

      I tried loading the files in Adobe Premiere 6.0 – but had the same result.
      My next step is to try the experiment with a different cam-corder – ie dv rather than digital8

      Is there a possibility that this has something to do with 29.96fps??

    • #175385
      AvatarAnonymous
      Inactive

      You all have my problem exactly.
      I recorded two 1 hour segments of a music show; both with a Zoom H4 ran through a mixing board, and a Canon ZR500.
      The sound did not match up. The fix was a nightmare. I cut up the video and matched up the sound. Overlaying extra clips to keep your eye off the guitar strum not matching the sound. shrinking the video would not work because the sound got progressively out of sync, so if I matched the end the middle would be sec off.
      I dont really want to talk about a fix for last time that is over. BUT if anyone finds a solution please post it. The way it stands now I will not use the Zoom for doing this again until I can save myself 40 hours of extra work !!
      Thanks so much,

    • #175386
      AvatarAnonymous
      Inactive

      Ill take your assault as a friendly one, with good natured intent, although in my defense I think that 30 years ago I was shooting weddings before almost anyone could afford to add motion to the subject, and a bride never gave a second thought to a movie. (also I threw my flash away and will not buy movie lights either but that is a subject for a different forum)
      Today I am trying to keep up with the times and add sound and yes motion to my work. Ill always believe in the power of the still image, but affecting the other senses of the viewer can be rewarding as well.
      http://www.leecraker.com/drop/index.html
      Although making the sound and motion work together seems to be a challenge at the moment.
      I sincerely hope we are not finding in this discussion that the Zoom may indeed be our problem, but if we are coming to that conclusion, at least it is good to forewarn those about to make a mistake.
      Thanks and happy shooting.
      πŸ™‚

    • #175387
      AvatarTEd
      Participant

      Lee
      I don’t have a total fix, but I found that if I cut two frames of Audio every minute – the sync was very good.
      I wan’t dealing with music, so it was easy to find a relatively dead spot in the sound track. That was much easier than mucking with the video – which was my first try.

      If anyone has a better fix – please post. The Zoom is such a great tool, I would hate to not be able to use it.
      Ted

    • #175388
      AvatarTEd
      Participant

      Hank
      Did that – see my previous post. When recording in MP3 format there is significant difference…when in Wav Format much less – around 2 seconds over 30 minutes.
      The Camera was the most accurate (type sync on the digital video file exactly matched the stop watch).
      The audio when loaded on either Ulead 10 or Adobe Premiere was about 2 seconds out.
      Splicing out about 2 frames of audio every minute seemed to correct the problem, but is very time consuming…

    • #175389
      AvatarTEd
      Participant

      Hank
      Thanks – I agree. I have contacted their support directly and will give them a chance to resolve the issue. Maybe there is a software upgrade or something…
      I will post any advise they give.
      Thanks
      Ted

    • #175390
      AvatarAnonymous
      Inactive

      Ted, Hank,
      Yes I was using a WAV file and the sync was only off 4 seconds over 2 hours. But progressivly. In other words tons of work man. We were using two cameras and the vids, were easy to match up, but not the sound. In any case if this is a Zoom problem I am real interested to hear what Zoom has to say. I agree it is a good recorder, great sound and features, but if it has this type of problem it is a plastic piece of junk when making movies, to be avoided to say the least.
      Please post when you get reply from Zoom corp.
      Thanks.
      PS The RMI is OK, Balli is better for fun and the eye, but I’m documenting the people here, a 2 year project.

    • #175391
      AvatarAnonymous
      Inactive

      Sure Hank …
      You can see allot of the stills here under "People of the Atoll"
      http://www.digitalrailroad.net/leecraker/Default.aspx

    • #175392
      AvatarAnonymous
      Inactive

      Thank you Hank … I try, I don’t always suceed… but I try

    • #175393
      AvatarMikeAiken
      Participant

      I’m also having the exact same problem and I’ve seen it now with two different Zoom H4s. The audio from the H4 lags after the video by about 2 frames about every 4 minutes. Never had this problem with my old MD recorder, stayed dead on for hours. I’m also correcting by cutting a few frames out of the audio every few minutes, but this is not going to be acceptable. I really like the H4 and would hate to have to give it up. Please, everyone, keep us posted with any news you may have about this problem.

      As far as sample rates, etc., I don’t think that has anything to do with it. It’s pretty obvious that the timebase of the H4 is not accurate. The clock speed of the processor must be wrong and this is always crystal controlled. If they’ve used the wrong or defective crystals, I doubt that anything simple can be done to correct it. Good luck folks!

    • #175394
      AvatarMikeAiken
      Participant

      I, and it appears that quite a few others from my internet searching, have discovered a problem with the Zoom H4’s timebase accuracy. I bought this unit to record interviews and audio for video of musical performances, but I find that when trying to sync the audio from the H4 with my video, the sound lags the video after just a few minutes. After doing some tests by recording a shortwave radio tuned to the National Bureau of Standards time signal for over an hour, I’ve found that the recorder is slow by about 1.069 seconds every 39 minutes (this was the closest to 1 sec. of error I could measure, hence the odd choice of numbers to report). While this is not a big deal when recording for audio only, It’s not usable at all for video when trying to maintain lip sync and fingers on stringed instruments. I corrected it on the first project that I used the H4 for by splitting the audio file about every 3 minutes at a quiet spot, and cutting out the equivalent time of about 2 frames of video. This is not going to be acceptable on long video projects. I’ve experienced this exact same problem on two different H4s recording the same performance at the same time and read about it from others on different forums.

      Please tell me that there may be some fix for this because I really love this little recorder and don’t want to have to give it up. I done this same type of thing with an old MiniDisc recorder for years and never had a single problem with time accuracy, but those are not readily available anymore and are too much trouble with external mics and discs, etc. PS. I’m not even going to mention the "beep" problem with the H4s. I have heard it, by really trying to make it happen, but it’s not an objectional concern to me. Please, please, tell me something can be done.

    • #175395
      AvatarAnonymous
      Inactive

      A reviewer on B&H states:
      "The only minor problem I have experienced is keeping the
      audio and video in sync. With my camcorder the audio needs
      to be stretched by 100.049% to stay in sync. This is a very
      simple solution with the right software, but it caused some
      frustration until I worked out the ratio which seems to be very
      consistent with all of the recordings I have made so far."

      Anyone have any comments about the 100.049% will this wotk, do you think?
      Thanks

    • #175396
      AvatarMikeAiken
      Participant

      Wouldn’t work for me because the audio in my case need to be shrunk, not stretched, the audio starts to lag behind the video and you can see that it’s already stretched on the timeline. I’ve tried just guessing around at changing duration to 99%, 99.5%, etc, but I really don’t know how to work the math to do it exactly. When guessing, it takes a pretty long time to render the audio and see if it’s close, but I do feel that this might be a good solution if we can figure out the ratio. ‘Nother question to toss up, would the adjustment percentage stay the same for different lenghts of audio track or have to be adjusted for every different time length?

    • #175397
      AvatarTEd
      Participant

      Below is the response I recieved from the H4 Samson product support.
      I am not convinced that it is my Camera – as I haven’t had similar sync issues with other recorders.
      I will be trying some tests with a different camera.

      Ted

      The H4 does records in PCM linear format in real time. It sounds like the problem is with your camera and it’s drop frame time code.
      Samson Technologies does not distribute nor support Zoom products outside of the U.S. For more assistance, please refer to http://www.zoom.co.jp to find your local distributor.
      Thank You,

      Rob Garofala
      Samson Product Specialist

      1-800-328-2882

      rgarofala@samsontech.com

    • #175398
      AvatarAnonymous
      Inactive

      In my case I was shooting with 2 different cameras. The sound was out of sync with both.
      Following Zooms logic all of us have defective cameras. Also in my understanding drop frame is a way of counting frames, and does not affect real time recording.
      Also the second camera in my scenario was shooting in non drop frame mode.
      Forgive my jumping to conclusions but it does seem to me like Zoom is saying Im doing it right while the rest of the world is wrong. Perhaps with prodding they can come up with a better answer?

    • #175399
      AvatarMikeAiken
      Participant

      I think I proved that it’s not the cameras by recording WWV from a shortwave radio. After 1 hour of recording the Zoom was off by 1.849 seconds. I opened the wave file in Audition and trimmed it to start exactly at the "zero minutes" beep. The next "zero minutes" beep was at 1 hour, 1.849 seconds on the timeline. How long did it take you to get this reply from Samson tech support?

    • #175400
      AvatarTEd
      Participant

      The reply took about a month. Because I am in Canada, they apparently won’t provide support to me.
      Perhaps the support would come more quickly to a US based customer. Please keep me advised if you have any luck. Like you, I love the recorder, but it will go up for sale on ebay if I can’t get around this sync issue. Thanks Ted

    • #175401
      AvatarAnonymous
      Inactive

      I purchased the H4 after reading the review in vidmaker. I wanted to have some extra audio to use , I had not seen this thread about the sync. problems . Lucky for me I only needed extra sound track material. I did go to the Zoom Corp. web site to see if this issue had been addressed and the new System version update 1.30 added 3-30-07 says;
      The latest System version 1.30 is released. The major changes from previous version are as follows.

      Supported Windows Vista for USB audio interface/USB card reader function.

      Deleted host PC select function, as we found problems in added Win mode at Ver1.10, intended stop in recording or out of sync happen depending on performance of PC, when using downloaded ASIO driver from our website.

      … So I guess that if you are on windows you have a problem with snyc.? well I could not get my H4 to update to version 1.30 πŸ™ after some e-mails (3) πŸ˜• I was told that the update is sent to your SD card as a Zip file that has to be extracted before the H4 will update.
      So now I have Version 1.30 software running in the H4 πŸ˜€ I hope that I can save someone out there an hour of time by posting the experience that I have had with the H4 and the zoom corp. web site πŸ˜‰ … CB

    • #175402
      AvatarAnonymous
      Inactive

      The update addresses the issue of recording directly to your pc with recording software ,as I understand it, and not the time code issue which has nothing to do with your processor speed.

    • #175403
      Avatarrogs
      Participant

      I posted a procedure here, which I’ve found useful for helping with sync problems.

      It’s a bit long winded, but you only have to do it once!

    • #175404
      AvatarMikeAiken
      Participant

      Thanks rogs! That’s exactly the solution that I thought might be possible but I didn’t know how to go about figuring it out. It may be a few days before I get a chance to try it, but I’m really excited because it certainly sounds like it should solve the problem. Thanks again!

    • #175405
      AvatarMikeAiken
      Participant

      I could never get the percentages for stretching or shrinking the files to work exactly right. I feel pretty sure that the internal clocks of the Zoom recorders may be a little different for individual units, however, I just now found another way that works. The problem is that the timebase for the Zoom is a little different from most computers, but if you let the Zoom play back the file from its card (not copy thecard directly into the computer) it all works out. I used the line out from my Zoom into my audio interface and recorded the playback from the Zoom into Audition. Then I pulled the file into Premier and synched it with the video and camera soundtrack at the beginning. It stayed in perfect sync for about 25 minutes (that was all I captured so far). I hated to convert back to analog but the quality of this little recorder is so good I can’t hear any difference, and I can deal with the time it takes to do it compared with cutting out a few milliseconds of the audio track every few minutes. Hooray! I’m happy with the zoom again.

    • #214671
      AvatarHarlin
      Participant

      I know this is a very old post but for anyone having problems with sync read on. I did a one hour band video using 3 sony nx5u cams and a Tascam DR-05 portable. Its the second recording in 2 weeks. First one I used mp3 files and sync went out a second or so in an hour. Second recording used wav file and same issue..Best way to deal with this is make sure all cameras are recording sound. Load audio in premiere cs6 find audio drum hit and store marker. drag audio to first audio track. Now load all video tracks one at a time and store marker at same point. I show audio files for this and then back to composite and drag to timeline and match markers. Since audio will drift some I will cust the main audio after every song during silence or room noise and hold alt and using arrows move 1-2 frames until drum hits line up. same for every song. extra work but easiest way I have found over the years..as a side note my old portable recorder (M-audio) would go for an hour and be exact to the frame in sync but no external mics.
      Hope this helps someone,
      Harry

    • #214687
      Avatarpaulears
      Participant

      I think he was asking too much. 30 minutes is 86 million samples. In an ideal world, we’d have them all, but the reality is that the clock in these devices is not accurate. Many very expensive devices run from a master clock, so sample rates are accurate, or at least all the same.

      Assuming all his clocks were free running, then there would have been discrepancies in the timing with long clips. If you don’t get them you are lucky. I do music videos quite often, and syncing is always like this. Worse when you mix brands and add in Chinese go pro types that drift even more. I tend to do re-syncing on the tracks every 20 minutes or so, and it’s annoying but common. In my theatre work – i get 60 minutes on sound and picture and I like my zoom – I don’t think a few frames in a long clip is a big deal – just annoying. I really wouldn’t assume anything is faulty or a poor product – 50 frames in how many million?

    • #214693
      AvatarHarlin
      Participant

      As a side note about sampling rate..Video audio is 48K always!!
      Audio like cd’s is 44.1..Always..If you mix and match you are asking for trouble. or at least noisy and sloopy conversions.

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