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TOPIC: Audio doesn't tie in with waveform

Audio doesn't tie in with waveform 1 year ago #199972

  • Triplog
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Hi. I hope I can explain this clearly. I edited a video (with no sound) then added a music backing track and synched up the beat of the track with the edit cuts in the video and exported it. All worked successfully. However when I went back in do some fine tuning I notice that whilst the sound and video are still in perfect synch, the waveform for the audio is approx 18 milliseconds in front of the actual sound. This makes it difficult to do any subsequent tweaks! I've attached a screenshot of this. The beat is the maximum point to the left of the red line and the red line is where the beat is heard. Can anyone shed any light on this?
Thanks in anticipation.

A quick edit to add that closing down LW the first time made no difference, but the second time on re-opening - everything lines up perfectly!!! Obviously not critical now but I'm curious.........
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Last Edit: 1 year ago by Triplog. Reason: added info

Re: Audio doesn't tie in with waveform 1 year ago #199975

  • hugly
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Hello,

I would think tewaking sound in a time range of 18 millisecond is the domain of DAW's with dedicated soundcard and ASIO driver.

I wonder which instrument did you use to detect a deviation of 18 milliseconds between the waveform and audible sound. How did you bypass the native OS audio device?
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Last Edit: 1 year ago by hugly.

Re: Audio doesn't tie in with waveform 1 year ago #199976

  • schrauber
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If I look at the timeline scale, it seems to be about 300 to 600 ms, depending on the frame rate chosen in the project settings.
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Software: Lightworks 2020.1; || Windows 10, 64 Bit
Hardware: Intel i5-4440 (3,1 GHz); || shared RAM: 8 GB; || Intel HD Graphics 4600 (can use max. 2 GB of shared RAM)

Re: Audio doesn't tie in with waveform 1 year ago #199977

  • hugly
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Ah, yes. 300 to 600 ms deviation are quite good detectable by human ears and eyes without any measuring device.

If the problem appears randomly and if it's fixable by restarting Lightworks, it could be that you still run Lightworks V14.0. If so, upgrading to V14.5 might improve the situation.
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Re: Audio doesn't tie in with waveform 1 year ago #199991

  • Triplog
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Thanks to you both for the replies - I'm currently running 14.5. Sorry about the misleading info. I read the lag off the timeline scale and forgot to convert it! It's obviously not a massive problem when re-starting cures it. Just for information - it was happening both in Fixed and Flexible layouts.
Thanks again

Re: Audio doesn't tie in with waveform 1 year ago #199992

  • hugly
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It shouldn't happen with V14.5 anymore. The issues, known from V14.0, which cause audio to be suddenly out of sync while editing, are assumed to be fixed with V14.5.

Do you know any procedure, a sequence of editing actions, to force the issue?
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Re: Audio doesn't tie in with waveform 1 year ago #199993

  • schrauber
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If on my system the audio starts with a delay when Playback starts, then that's a sign for me that I need to restart Lightworks.

Triplog wrote:
... I edited a video (with no sound) then added a music backing track and synched up the beat of the track with the edit cuts in the video and exported it...

I first analyze the audio (waveform and acoustic), and place "Cue" in the audio source itself. In the following processing in the sequence timeline, I mainly orientate myself on this cue, so that the waveform becomes secondary. If I have also placed a Cue in the video, then I only need to match the correct Cue, which often works with a few keystrokes (or match the audio cue with the video cuts).

For an efficient workflow with Cue there are some details to consider. More at Interest ...
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Software: Lightworks 2020.1; || Windows 10, 64 Bit
Hardware: Intel i5-4440 (3,1 GHz); || shared RAM: 8 GB; || Intel HD Graphics 4600 (can use max. 2 GB of shared RAM)
Last Edit: 1 year ago by schrauber.

Re: Audio doesn't tie in with waveform 1 year ago #199994

  • jwrl
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I think that both hugly and schrauber may have misread your original post, Triplog.

Triplog wrote:
I notice that whilst the sound and video are still in perfect synch, the waveform for the audio is approx 18 milliseconds in front of the actual sound.

As I read that, the sound isn't out of sync but waveform display is. You also go on to say that after restarting Lightworks, the waveform display matches the sound which apparently is still in sync with the video. So the issue is one of display not of sound sync.

It should be possible to estimate whether a waveform is offset from a frame boundary by 18 ms or not. At 30 fps that's around half a frame. What isn't possible is for human beings to reliably hear that small an offset even if it's leading picture. The average person cannot hear sync errors of .6 of a frame leading at 24 fps. That equates to 25 ms.

Lagging sync is even more forgiving. The average person cannot hear sync errors of less than 1.5 frames at 24 fps, or over 60 ms delay. Some measurements even push that out to around 90 ms. I err on the side of safety and take the smaller figure as reference.

I'd like to meet that average person! What it comes down to is this: while it's very "purist" to sync audio by waveform it's ultimately not that important. If it feels right it is right.
Last Edit: 1 year ago by jwrl.

Re: Audio doesn't tie in with waveform 1 year ago #199998

  • RWAV
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It also opens the discussion about the intrinsic difference between sound and picture acquisition - sound is (essentially continuous even in digital formats) picture is a series of static images with, depending on acquisition technology, sections exposed/recorded over a period of time. One will always hear the sound of a camera flash but will not always see it's peak brightness.

Watching a drummer - one will interpolate the exact moment of impact while watching the image stream - even if the actual impact is never seen in any frame.

18 milliseconds is well and truly within the relative 'error' range.

(That's probably also missing the OP's original point)
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Last Edit: 1 year ago by RWAV.

Re: Audio doesn't tie in with waveform 1 year ago #200001

  • Triplog
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Hi jwrl and RWAV. Add I said earlier I was wrong in stating 18ms, hugly was correct as it's about 400ms. Jwrl you are correct in that the audio is always in synch with the video, it's "out of synch" with its own waveform! Restarting has cured the anomaly and it hasn't reappeared!
As for the rest of the answers given, a lot of it is over my head! Like driving in fog, sometimes I think I can nearly see it!!! Being in my 60's now and coming from a stills background (good old rollfilm and a darkroom!), I use Lightworks at a fairly basic level, but enjoy the challenge immensely.

Re: Audio doesn't tie in with waveform 1 year ago #200023

  • jwrl
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Triplog wrote:
Being in my 60's now and coming from a stills background (good old rollfilm and a darkroom!)

'60s? You're just a baby! I'm a WW II child.

My first film processing was reversal - Ektachrome E3. Having mastered that I followed it a little while later with reversal colour printing. I then graduated to B & W. I've always done things backwards.

My favourite chemistry was Acutol fixed with M & B fixer. Acutol was an extremely fine grain high acutance developer that also increased the effective ASA rating of the film stock by a third, so you got three pluses with it. I used a range of paper stocks but my real favourite was Agfa Portriga, which had beautiful warm chocolate blacks. Unfortunately I no longer have an enlarger or developing trays or tanks.

Do I miss having my hands in chemicals? You bet!
Last Edit: 1 year ago by jwrl.

Re: Audio doesn't tie in with waveform 1 year ago #200058

  • Triplog
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Oh man now you've got me going!!! FP4, PanF. Just mentioning Acutol brings the smell back! Processing colour slides stressed me more than work or children ever could! I gave all that up when I converted to digital (a Canon with 3mp and a 1" screen!!!). The problem with LW is I don't get as much time as I'd like with it to become better, it always seems to be firefighting! I admire an am envious of all you guys who are so knowledgeable (and generous with your time and patience).

Re: Audio doesn't tie in with waveform 1 year ago #200063

  • RWAV
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Triplog wrote:
it's "out of synch" with its own waveform! Restarting has cured the anomaly and it hasn't reappeared!
Is there any chance the error condition occurred while LW was still writing the file's waveform information??
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Re: Audio doesn't tie in with waveform 1 year ago #200080

  • Triplog
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If I understand correctly what you're asking, no. I had opened LW after a previous editing session. It had been open a while and I played various parts of the sequence then moved between Flexible and Fixed layouts for comparison. The problem vanished after re-opening (and hasn't returned).

Re: Audio doesn't tie in with waveform 1 year ago #200090

  • RWAV
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Sorry I wasn't clear - was asking if perhaps in the original error event LW was still writing the waveform data (it only writes it once) at the same time as the file was being accessed in a viewer. For large files it can take enough time for that to be a possibility.

Just looking for some reason why the error happened once and has not repeated subsequently.
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