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Thread: Synchronizing WAV with Video

  1. #1

    Default Synchronizing WAV with Video

    Hello All,

    I need some help synchronizing my WAV files with my video. Here's my set up:

    JVC DV Camcorder (29.970 fps)
    Laptop recording in WAV
    Sony Vegas 5.0 Editing SW

    I'm using the camcorder's audio as a scratch track, but I'm having a very difficult time synchronizing the two sources. I know I'm having an issue with the fps, but I'm not sure what to do about it.

    Can anyone recommend a good method of synchronizing the two sources?

    Thanks,

    Faust13

  2. #2
    Join Date
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    Theres only one way.
    With both the video soundtrack and the WAV file on the timeline and both active, find a sound early on in the recording that is clearly audible in both soundtracks (a clap, drumbeat or similar) and slip the .WAV along the timeline until that sound coincides roughly with the video sound. You will then hear an echo effect because the two are not perfectly in sync. so keep nudging the .WAV clip one way then the other until the delay reduces and evenutally, with patience, the two will 'snap' together and there is no delay or echo at all.
    Once the beginning of the recording is in sync., go to the end of the recording and see how much delay there is - external recordings will rarely stay exactly in sync for more than a few minutes before they drift. If there is an audible delay then you need to cut the .WAV clip at various points in the recording and slip it back into sync until the whole thing sounds OK. Its a pain, but its the only way.
    I find it better to take the audio output from the laptop or mixer and record it on any old spare DV camcorder then capture it separately. You will find that the audio will then stay in sync with the video for recordings of an hour or more.

  3. #3

    Default

    Quote Originally Posted by GentleGiant View Post
    Theres only one way.
    With both the video soundtrack and the WAV file on the timeline and both active, find a sound early on in the recording that is clearly audible in both soundtracks (a clap, drumbeat or similar) and slip the .WAV along the timeline until that sound coincides roughly with the video sound. You will then hear an echo effect because the two are not perfectly in sync. so keep nudging the .WAV clip one way then the other until the delay reduces and evenutally, with patience, the two will 'snap' together and there is no delay or echo at all.
    Once the beginning of the recording is in sync., go to the end of the recording and see how much delay there is - external recordings will rarely stay exactly in sync for more than a few minutes before they drift. If there is an audible delay then you need to cut the .WAV clip at various points in the recording and slip it back into sync until the whole thing sounds OK. Its a pain, but its the only way.
    I find it better to take the audio output from the laptop or mixer and record it on any old spare DV camcorder then capture it separately. You will find that the audio will then stay in sync with the video for recordings of an hour or more.
    Thank you for the suggestion. I can get it to synch up, but within 30 seconds or so, it starts getting out of synch again. Is there really no better way than arduously hand adjusting it?

    Unfortunately I do not have a spare DV Camcorder for audio capture, I'm in this situation, because my DV Camcorder does not have a mic input. I have plenty of audio equipment, but no good approach for synching the two.

    Thanks again!

  4. #4
    Join Date
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    Losing sync after only 30 seconds sounds a bit extreme - was the audio recorded on an analogue or minidisc recorder then digiitised on the laptop ?
    Alternatively, since Vegas is well known for being good at audio manipulation, it might have a tool for stretching the audio to fit the video - I don't know Vegas so try asking the experts in the Vegas forum.
    Failing that, you could try to find someone who is running heavyweight audio software like Cubase or Audition which can edit audio synced up with video.

  5. #5

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    It's strange, I put the two sources on the timeline, and by the end of the video, I have almost 2 seconds extra of audio. I can't explain it. Neither audio track on the video (scratch) or WAV sounds unusual (i.e. pitch shifted).

  6. #6
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    The problem may because the two audio tracks have different sampling rates.

    Sync problems can occur when one track is sampled at, say, 48,000 Hz (the camcorder track) and the other is at 44,100 Hz (such as an audio track from a CD).

    Were the WAV files recorded using the latter sampling rate?


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  7. #7

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    Quote Originally Posted by bert6280 View Post
    The problem may because the two audio tracks have different sampling rates.

    Sync problems can occur when one track is sampled at, say, 48,000 Hz (the camcorder track) and the other is at 44,100 Hz (such as an audio track from a CD).

    Were the WAV files recorded using the latter sampling rate?
    Good call on the sampling rates. My original WAV was sampled at 44.1 kHz, whereas (checking the manual) my DV Camcorder samples at 32 kHz. I tried to resave the WAV as 32 kHz, but it didn't seem to have any impact on the audio track running longer than the video's audio track.

    If I had recorded my audio initially at the same sampling rate, would they have "snapped" together? Is there anything I can do to synch my existing audio track?

    Thank you both so much for your help!

  8. #8
    Join Date
    Feb 2007
    Location
    Portland Oregon
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    I found out about something yesterday that made me really happy. I had an hour long Mythbusters file that was 7 seconds out of sync. I looked it up on google and I found:
    How do I fix audio sync in AVI file ?
    I tried it, I plugged in my AVI file and it imediately exported one that was 100% correct. I got really excited.
    -Ethan


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