Quantcast Odd audio popping on linear audio track? - digitalFAQ Forum
  #1  
03-05-2021, 12:32 AM
ENunn ENunn is offline
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Yesterday I got a batch of tapes. They haven't aged well. It was recorded off DirecTV and I guess a messed up deck. Some of these tapes don't got a HiFi track. Unfortunately the normal linear track doesn't sound good at all. I can expect the normal muffleness but this one had this awful constant popping and digital bloops in it. I have an example attached. It isn't typical static noise. I've never had tapes with audio this bad before. I tried two different VCR's, messing with the tracking. One VCR minimized it but it slowly came back. Is there anything I can do or am I out of luck? Kinda sucks in this case too, this is some rare stuff that you don't usually find online


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  #2  
03-05-2021, 09:24 AM
timtape timtape is offline
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Quote:
Originally Posted by ENunn View Post
Unfortunately the normal linear track doesn't sound good at all. I can expect the normal muffleness but this one had this awful constant popping and digital bloops in it.
Sounds like what's called "motorboating" due to a faulty amplifier somewhere in the chain. I notice on the spectral analyzer it seems to change in frequency a little, as if some of the picture signal (changing image) is bleeding into the audio, but cant be sure. Having a little expertise in this audio area I'd probably try temporarily alterating the A/C head height to see if it made an improvement. Please dont attempt this unless you have the skills and knowledge.

Yes it's sure muffled. There seems a nasty dip in the spectrum around 3 kHz which degrades speech clarity. The entire audio track could probably be brightened up considerably with one small tweak of the A/C head azimuth screw but again unless you know what you are doing please dont attempt this. The same for adjusting A/C head height. These are specialist custom tweaks.

IF there was nothing else I could do, I'd probably high pass filter the audio, cutting the lows below about 250 Hz. It wont totally remove the noise but reduce it at the cost of reduced bass in the wanted audio. For a more targeted approach I'd try a narrower band De Hum filter.

In your sample there's loud talking, band, audience going on, making it hard to get a real handle on the noise characteristics. I'd look for a quiet section of the program where the pulsing can be heard clearly. It might help if you upload such a quiet passage so the noise can be more easily analyzed and commented on. Find a place in the tape where ideally only the problem noise is present. No dialogue, music, effects etc.

Changing the tracking control shouldnt make any difference to the linear audio track. It only affects the video and HiFi audio.

Last edited by timtape; 03-05-2021 at 09:56 AM.
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  #3  
03-06-2021, 07:43 AM
Cactus Cactus is offline
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Using the noise reduction in Adobe Audition, I found the most isolated noise and did a quick and dirty clean. (Dirty clean??) It came out fairly well but it might be too aggressive. As timtape says, find somewhere where there is nothing but that sound, and you should be able to salvage it fairly well if you can't help it hardwarewise. And if it's in the recording itself, which is fairly hissy anyway, then this is the only thing you can do.

Note: there are other noise reduction softwares out there, but I'm not up to date with what's the best.


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  #4  
03-06-2021, 11:24 AM
ENunn ENunn is offline
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I can do some noise reduction, that's fine. I do it for all my tapes. The problem is that popping sound. It's gonna be really difficult to minimize it without destroying it too much
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03-07-2021, 03:04 AM
Cactus Cactus is offline
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Quote:
Originally Posted by ENunn View Post
I can do some noise reduction, that's fine. I do it for all my tapes. The problem is that popping sound. It's gonna be really difficult to minimize it without destroying it too much
I didn't just do a hiss noise reduction, I got rid of the "motorboat sound". Have a listen.
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  #6  
03-07-2021, 07:17 AM
timtape timtape is offline
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Quote:
Originally Posted by Cactus View Post
I didn't just do a hiss noise reduction, I got rid of the "motorboat sound". Have a listen.
Yes a lot of the motorboating in the bass end has been reduced but a lot of the wanted bass in that same region has also been reduced. Removing broadband interference like this without creating other problems is difficult if not impossible.
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  #7  
03-07-2021, 04:37 PM
timtape timtape is offline
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Here's a spectrum screenshot. The fine vertical lines at the bottom of the screen (deep bass region) show the motorboating noise best. The pulses occur 9 to 10 times per second. There's probably more of the noise further up too but a lot will have been masked by the loud program. A quiet section with no program, only the motorboating, would give a better idea of its characteristics.


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