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Old March 20th, 2005, 02:10 PM   #1
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LP metalic noise

Hello there,
I'm now editing a small project, which uses home-video matrial shot in LP, 16bit. the problem is that quite often there is this short "buzz", like a digital scratch. (a ssssss very digital sound) which only occurs for a short period but is horrible.

Does anyone knows of this, and a possible way of reducing it ?

TIA,
Alon.
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Old March 20th, 2005, 03:34 PM   #2
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If you record LP mode (mini-DV) you greatly increase the chance of dropouts (audio and video). If you hear glitches (very short, totally random noise) it might be because of dropouts. You should also see video dropouts, which are rectangular blocks that happen to individual frames.

It could be something else entirely too.

Some things you can try:
A- If it's voice, you can filter out high frequencies so it doesn't sound as bad. Parametric EQ filters and Waves' Linear EQ filter are good for this, or you can use normal EQ filters and stack them if you need a sharper rolloff. I don't think this will help too much though.
B- You could use Soundforge or a similar program to edit the waveform manually where there are dropouts. Very time consuming.
C- You can paste bits of good audio from other places. If you want to do this to dialogue, Jay Rose's books has some great information and tricks on doing this. see dplay.com to buy either of his audio books for $30
D- If the audio is bad because of dropouts, try capturing again. Even better, use the camera that shot the material or a high-end DV deck with good tracking.
In your editing program, lay both tracks of audio side by side and cut to the other captured audio when there are dropouts.
Perhaps the dropouts are such that they are easy to spot visually on a waveform.
You can also try running a mini-DV cleaning tape through your camera beforehand. Even better would be to clean your camera manually as cleaning tapes are kind of for emergencies (make sure you find good instructions though). This will solve dropout problems from dirt on the camera's heads or lubricant mixing issues, which do cause dropouts but probably isn't causing dropouts for you.

2- If you could find out the cause of the problem or post a clip up of your audio that can help too. Perhaps your problem is not audio dropouts.
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Old March 20th, 2005, 04:38 PM   #3
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If you shot this in LP are you sure it's not 12 bit?If you have 12 bit on a 16 bit timeline it could generate a few weird things
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Old March 20th, 2005, 04:41 PM   #4
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Audio can either be 4 channels, 32khz sampling, 12-bit depth or 2 channels, 48khz sampling, 16-bit depth

Most cameras can be set to display 12 or 16bit on the on-screen display when you play the footage back, so that's a good way to check things.
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Old March 20th, 2005, 05:13 PM   #5
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Glenn , some cams when set to record LP auto switch the audio to 12 bit 32k.That is why I posed the possibility.Alon could also check this from the timeline.Just a possibilty I thought was worth mentioning
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Old March 21st, 2005, 03:31 AM   #6
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Thanks all for the answers

The footage was shot in a very consumer mini-DV, and digitized thru my XL. AVID had hard time i.d.ing the original camcorder (panasonic ds-28, i think). Anyway, this is probably a drop-outs problem, although most of the time, it is noticable in sound only (not in the picture). I've viewed the sound track using Adobe Audition 1.5, and wasn't able to detect it visually. I also thought it will appear in the High Freq, and reducing those does help some, but it's all over the spectrum.

The most annoying thing is the charcharistic of the noise. if it was a simple hiss... but it's like dreaming a digital nightmare. I've noticed that it appears mostly when the volume is suddanly shifted - fot example, a girl sings and plays the guitar, and every time she sings "high", it makes that noise. A combination of LP and distorion?

Thanks for all the answers.
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