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Thread: Syncing separate audio, paull

  1. #1

    Default Syncing separate audio

    Hi guys, I'm a little new to this. I've done some (very basic) video editing, and I've seen how audio from an external recorder can be sync'd with video. I'm currently waiting on my sound recorder in the post, and I'm sure the answer to my question will perhaps become apparent, but I think it's probably obvious to you.
    I've seen how people clap at the start, then line the spikes in the audio, however, if the clip is quite long, I would guess that this timing needs to be adjusted throughout the clip ? I guess the whole audio is sync'd to the complete unedited clip, then the clip is edited as required.... and timing on the audio fine tuned ? And how is this done, what if you have no further claps, you just get used to the fact that it runs fast or slow, and adjust by ear ? ..... or am I imagining a problem that doesn't exist ?

    Last edited by Paul2129; 12-24-2016 at 03:53 PM. Reason: Typo

  2. #2
    Join Date
    Feb 2006
    Surrey, UK
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    Theoreticaly as both camera and audio recorder are digital they should not drift. I regularly shoot for 30 mins plus with a Canon XF100 and a Zoom H2 and have never experienced any drift. So it may not be a problem for you. However some people do report a problem so your mileage may vary.
    I makes sense to set the audio recorder sample rate/bitrate to match the video - although I've forgotten to do this at times and experienced no problem.
    Syncing without a nice sharp momentary spike like a clap is exactly the same principle, just not as quick.
    It's a case of getting it close then shifting the audio backwards and forwards until it sounds right.
    It ca be helpful to slow both audio and video tracks down if your NLE allows you to do that.

  3. #3


    Thanks for the info Tim. I'm
    Waiting on a 'reasonably powerful' laptop (hoping for something in the sale and for my Zoom H1 to turn up. My next step will be finding some (easy) video editing software... then I can start to practise. I've found it quite fascinating, I've only played with iMovie on the iPad, but even that seemed remarkably well thought out

    ....... I edited the typo in the title above, not sure what it was supposed to say

  4. #4


    As Tim has already suggested, ideally both the camera and the audio recorder should remain perfectly in sync, and for the most part this is true in practice. Things are certainly better than they were a few years back when some of the earlier cheap audio recorders has some very 'iffy' timing problems caused by the use of cheap crystals - or even ceramic resonators - used for their timing control.

    I made some notes about the problem for a friend a while back, which may be of use?....

    Audio Sync.pdf

    The most important thing to remember is that even if the audio recorder is spot on, and it's the camera 'clock' timing that is a bit 'off', then you still need to correct the audio recorder track length.
    The camera audio is always the master track. That's the one that's 'in sync' with the video!
    Last edited by rogs; 12-24-2016 at 08:22 PM.

  5. #5


    A further quick question. With my intended type of filming I could well have a couple of hours of footage, twinned with audio from the recorder to put with it. Only some of it will be used, maybe 3 hours of 'fairly continuous' footage will make a 40 minute video. Further to this, my camera records in 30 minute segments, between which it takes a couple of seconds to save the file, then it starts again. How will my sound be sync'd to this stop/start footage ? Do I load all the video into iMovie, then sync the audio, adjust it to be correct right through the entire footage, then chop up the completed video/audio to make the finished video ?
    This is probably totally obvious to you, forgive me for the daft questions.

  6. #6


    You are going to need a new reference point each time the camera effectively stops for a couple of seconds. There's no way the audio recorder can know the camera has reached it's limit every 30 minutes, and has introduced a 'gap' into the video proceedings!

    The only sensible way is to ensure each clip is less than 30 minutes long, and then make a new 'clapper' reference point at the start of each clip, which both the camera and the audio recorder mics can hear. (I usually lightly tap the recorder mic against the camera body). Nice sharp reference noise!.... You could also speak a few words, to help you identify each particular clip.

    Then take your raw video footage ( a series of less than 30 minute clips) and replace the audio using your reference clap points to sync it to the camera audio.

    Then edit the video clips as you need, knowing they already have their new audio already 'in sync' before you start...
    Last edited by rogs; 01-09-2017 at 09:23 PM.

  7. #7


    Thanks Rogs, I guess I can try a timer set at 30 mins, clap each time the timer sounds, then I can synchronise, and edit out the timer and clapping once the sound is in sync. I guess that once I've worked out that the time wasted by the camera is say 2 seconds.... at least I'll have a pretty good idea of where to find my audio if something gets messed up or I forget my timer. I'm a bit surprised that programmes like iMovie can't automatically sync the sound files with each other
    Last edited by Paul2129; 01-09-2017 at 10:01 PM.

  8. #8


    Quote Originally Posted by Paul2129 View Post
    I'm a bit surprised that programmes like iMovie can't automatically sync the sound files with each other
    You can buy a program that does it automatically - it's not cheap though!

    See here: Standalone,program - although you can import and export timeline sequences for FCPX (but not iMovie)

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