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TOPIC: Audio spike at a cut

Audio spike at a cut 2 years, 3 months ago #123386

  • Pandautz
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Hey there.
So I downloaded Lightworks a few weeks ago, and I absolutely love it.
I only use it for small video editing stuff, but I got one problem that seems to appear in most of my videos.
I´m going to try to explain it as well as I can.

So, the videos I edit for my girlfriend´s channel are always made in the same way. I put in the finnished intro, I put in the video itself, put in an endcard, and put in background music. The BGM loops a few times, and I usually put it at around -30 dB (so really just to have a little ambiente sound).
Now, the problem is, that in some videos (not all) there is an audio spike at the last moment before it cuts to the endcard, where I put different music.
Fact is, I put the sound at -30 dB, and I even do a fade out in the last 2-3 seconds, but there is still an around 0.1 second audio spike.
I tried cutting the BGM before the transition to the endcard, that just moves the spike a few seconds earlier.
The funny thing is: While in Lightworks, the spike is NOT there. It only appears when I export the video, and watch it in Media Player or on Youtube.

I hope you get what I am trying to say. I would post a link to a video where you can see (or hear) for yourself, but I think that´s against the rules, right?

Hopefully someone knows how I can fix it, since it´s really annoying.
If you need any more details, please tell me.
Thanks

Re: Audio spike at a cut 2 years, 3 months ago #123387

  • hugly
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Hello and welcome!

I encoutered spikes at end of a video using audio nodes to attenuate with V12.02 but not with V12.6 and not at a cut point.

What method do you use to attenuate or crossfade at the position the spike occurs? A screenshot of the section zoomed in to a few frames might be helpful.

What is the source audio format, PCM, AAC, MPEG2 ore something else?
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Re: Audio spike at a cut 2 years, 3 months ago #123389

  • donkpow
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As far as I know, it's not against the rules to link to or embed a video. What is frowned upon is copyright violations.
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Re: Audio spike at a cut 2 years, 3 months ago #123396

  • jwrl
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One thing that might be worth checking is that your audio soft cut duration is correctly set. In the top right corner of your screen click on your project name and select the audio option in the drop down menu. Soft cut duration should be set to at least 5 ms. Experiment with it a little - there are only three non-zero presets - it may help.

Re: Audio spike at a cut 2 years, 2 months ago #124351

  • Pandautz
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hugly wrote:
Hello and welcome!

I encoutered spikes at end of a video using audio nodes to attenuate with V12.02 but not with V12.6 and not at a cut point.

What method do you use to attenuate or crossfade at the position the spike occurs? A screenshot of the section zoomed in to a few frames might be helpful.

What is the source audio format, PCM, AAC, MPEG2 ore something else?


It took me some time to return here (forgot my password as well... -.-)
So, the quoted post I did not understand. Sorry, I am really not very versed in such things.

I tried to change the soft cut duration, all 3 possibilities, did not help...
Here is one of the videos with a cut:

(cut is at 10:34)
That is one of the less "strong" spikes.
In the uploaded videos there are a few with and a few without the spike.
Plus I didn´t come here to the forum, because the last few videos didn´t have it. Now it´s back in my current projects...

Re: Audio spike at a cut 2 years, 2 months ago #124355

  • hugly
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There are many ways to mutilate audio like this.

As I said above:

A screenshot of the section zoomed in to a few frames might be helpful.


EDIT: Just to make clear: I mean a screenshot of a part of your edit time line in Lightworks. This section should show what you did with the audio before and behind the cut point, something like this:

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Last Edit: 2 years, 2 months ago by hugly.

Re: Audio spike at a cut 2 years, 2 months ago #125077

  • Pandautz
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Ok, here it is.
Fully zoomed in, and zoomed out a tad bit.
As far as I can tell there is nothing visible...

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Re: Audio spike at a cut 2 years, 2 months ago #125079

  • hugly
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I'm pretty sure that the audio on track A3, A4 causes the spikes although it seems to be attenuated somehow.

How did you do this, Track Sound Level or Clip Gain?

What dB-values are shown at the cut point?


EDIT:
If the Track Sound Level (Advanced tab) of the last frame of A3,A4 doesn't show "mute" this can cause the spike.

To fade-in or fad-out to absolute silence there's an easy and secure method explained at pages 112-113 of the user guide, please see attached pdf. To fade-in and fad-out personally I use always this one.
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Last Edit: 2 years, 2 months ago by hugly.

Re: Audio spike at a cut 2 years, 2 months ago #125087

  • RWAV
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In your screen grab - are your audio waveforms set to display pre or post levels.

There is no intrinsic reason why LW would create an audio spike at a cut point on A3/A4 or on any other A track. Curious artefacts may possibly occur in highly compressed audio files - that is not to suggest it is so in your case.

Please set your waveforms POST levels and check for perhaps a spurious audio node as in the one I manufactured for the attached screen-grab. There should be absolutely no need to add an audio fade down and up again at every cut point.

Could you also please enable the timeline 'advanced' button and include the audio level and gain displays in your next screen grab.
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Re: Audio spike at a cut 2 years, 2 months ago #125088

  • hugly
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There is no intrinsic reason why LW would create an audio spike at a cut point on A3/A4 or on any other A track. Curious artefacts may possibly occur in highly compressed audio files

That's the point, AAC or MP3 containing high volume audio (e.g. music) together with audio nodes different from "mute" at the last frame before a cut can generate spikes because of the way AAC/MP3 is decoded. This is also true for the inpoint of the next clip. Fade-in from zero and Fade-out to zero with appropriate length will fix the problem, it did at least each time I've encountered the problem.


EDIT:

This problem isn't specific to Lightworks. It's related to the nature of decoding of compressed audio.
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Last Edit: 2 years, 2 months ago by hugly.

Re: Audio spike at a cut 2 years, 2 months ago #125089

  • hugly
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RWAV wrote:
that is not to suggest it is so in your case.

Yes and it isn't what I assumed above.

I downloaded the video posted above from Youtube and linked it to a 30fps project, audio video are out of sync because it's vbr out of Youtube but that doesn't any matter here. This screenshot shows the audible spike at appr. 10:34 (duration appr. 70 millseconds):

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To me this looks very similar to something which a switched off microphone would produce.

RWAV, what do you think?


EDIT: Same thing in Audacity, phase inverted though.

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Last Edit: 2 years, 2 months ago by hugly.

Re: Audio spike at a cut 2 years, 2 months ago #125096

  • donkpow
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That's the point, AAC or MP3 containing high volume audio (e.g. music) together with audio nodes different from "mute" at the last frame before a cut can generate spikes because of the way AAC/MP3 is decoded.
Uncompressed audio streams do not contain frames. "Frames" are unique to compressed audio streams. The visualization that Lightworks presents is based on uncompressed audio.
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Re: Audio spike at a cut 2 years, 2 months ago #125101

  • hugly
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donkpow,

have you seen this kind of spike as an artifact out of Lightworks somewhere or is it more likely that it's in the audio source?
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Last Edit: 2 years, 2 months ago by hugly.

Re: Audio spike at a cut 2 years, 2 months ago #125102

  • hugly
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Pandautz,

what do you think, does this spike visible to the right of your cut point show some similarity to the spike I found in the download of your video?


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Even though it doesn't show exactly the same shape it's obviously a spike with some distortion added. You might wish to search for existing spikes to the right of the cut point in your original edit.

EDIT:
And to all friends of pan slider setting discussions:

The amplification and distortion of the spike could be caused by pan slider default settings, which is centered and wrong when applied to stereo channels.
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Last Edit: 2 years, 2 months ago by hugly.

Re: Audio spike at a cut 2 years, 2 months ago #125105

  • donkpow
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I've seen a similar type of thing in Lightworks but the problem was corrected quite a while ago. Is this the Linux issue?
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