VCR audio interference helicopter sound?

[BarryTheCrab]

Some tapes, on some machines, make this whoopwhoop distant helicopter sound, and I cannot seem to identify the cause.
My 2 JVC 7800(and the 2 Philips by JVC) all have this audio (on certain tapes).
My JVC365u does not, and my Toshiba W808 does not.
Everything is on a UPS, and in the past I have tried different capture software, cables, shutting off my electric heat, shutting lights, moving my router.
I'm even starting to think about if our power supply changes a little during the day/night. Some places do that, maybe? Is that a thing? Just asking.
Attached is a sample for the audio, never mind the video it's not optimized for anything.
I have never been able to pinpoint a common denominator but perhaps the actual sound will narrow my search for a solution.
Any insight would be greatly appreciated.

[latreche34]

It sounds like the tape was recorded with a mis-aligned VCR, What you are hearing is the linear audio head scanning the tips of the video tracks which is usually the VBI section. If linear audio is the only audio track you may have to miss-align the stationary audio head of a spare VCR to get a perfect audio.

[BarryTheCrab]

Thank you, "L34".
That is almost encouraging, because I try to get decent audio and if it's baked into the tape (one of my suspicions) then at least I have an idea of what I'm up against. More opinions always welcome.

[timtape]

Quote:

Originally Posted by latreche34

It sounds like the tape was recorded with a mis-aligned VCR, What you are hearing is the linear audio head scanning the tips of the video tracks which is usually the VBI section. If linear audio is the only audio track you may have to miss-align the stationary audio head of a spare VCR to get a perfect audio.

My audio analyzer displays 10 of the pulses per second. Does that correlate?

[lordsmurf]

Quote:

Originally Posted by BarryTheCrab

Some tapes, on some machines,
Everything is on a UPS,

Look around your environment. What else could it be? It may be aerial, not through wires.

You can always DIY an EM cage.

[aramkolt]

Does it do it on the mono/linear audio too? If it does, shouldn't be a head alignment thing. There should be an A.Monitor button on your remote to cycle through different options and the front display will change showing L+R, L, R, and showing neither L or R and that's the mono audio.

[BarryTheCrab]

All manner of audio settings fail to make it go away. Using different VCRs will mitigate or eliminate the noise, but it's never the VCR I want to use! Often the tape apparatus of the original camcorder hides the noise, but silence can be deadly.
I need to pick a single tape that is particularly noisy, and use that as my testing baseline, that way I can at least make notes of time of day, machine, whatever.

[timtape]

I dont have Barry's tape to test so instead, on a VHS tape with picture but no audio recorded I lowered the linear audio head so that it just started picking up the top edges of the video write stripes. Audio file below.

The sound is very different from Barry's "helicopter sound". It's less a deep pulsing and more a strident chirping sound. Barry's sound has 10 pulses per second where here it's 25 chirps per second (PAL system)
When I wound the A/C head even lower the sound was muted out, I guess because the control track started to miss the control head. The VCR must have assumed the recording had finished and muted the sound.

Sorry that doesnt shed any light on the cause of Barry's pulsing sound.

Lowering the A/C head can be tricky to do without altering the head's perpendicularity. I wouldnt recommend it unless you're skilled with setting up an A/C head. Even I can find it a tricky job depending on the VCR.

[BarryTheCrab]

I wouldn’t dare! The interference is probably external, in my view.

[timtape]

Could be. Have you eliminated the mobile/cell phone?

[latreche34]

It doesn't have to be video, it could be caption or teletext data that only pulse in 1/3 of the frames, but since I don't know much about the tape, these remain pure speculations. Electromagnetic interference from nearby electronics will be high frequency buzzing like an old school dialup modem.

[timtape]

Quote:

Originally Posted by latreche34

It doesn't have to be video, it could be caption or teletext data that only pulse in 1/3 of the frames, but since I don't know much about the tape, these remain pure speculations. Electromagnetic interference from nearby electronics will be high frequency buzzing like an old school dialup modem.

If you're familiar with this on teletext or caption data could you upload an example of it bleeding into the audio head so we can compare the sound with that on Barry's example?

[RayNotes]

One simple test is to capture the same bit of footage several times. Align each take in an editor and examine the interference pattern. If the interference pattern is identical in each take, the problem is most likely local to the tape or at least your machine's interaction with it. If the pattern varies between takes, it's most likely external to your equipment.

[dpalomaki]

Opening the file it in Audition I see 25 ~8 ms bursts of ~3 kHz sound per second in with the other noise.

PAL frame rate

Waveform (amplified 20 dB) attached.

To rule out issues related to the playback location take take the VCR a few miles away and play the tape. If the noise is still present it would strongly indicate it is the VCR interacting with the tape content.

[lordsmurf]

The power grid can also be an issue, so a few miles may make no difference. In the 2000s, on the TVA, DataVideo gear did not work correctly for me, even 50 miles away. It'd pick up grid power noise, even through UPS. I didn't like TVA power, the voltage was too variable, and would sometimes trip my breakers. I even had part of the house re-wired, but it was new construction, and they never found interior faults. It was never resolved, and I was forced to move due to health.

[timtape]

Quote:

Originally Posted by RayNotes

One simple test is to capture the same bit of footage several times. Align each take in an editor and examine the interference pattern. If the interference pattern is identical in each take, the problem is most likely local to the tape or at least your machine's interaction with it. If the pattern varies between takes, it's most likely external to your equipment.

Good advice, RayNotes.

[timtape]

Quote:

Originally Posted by dpalomaki

Opening the file it in Audition I see 25 ~8 ms bursts of ~3 kHz sound per second in with the other noise.

PAL frame rate

Waveform (amplified 20 dB) attached.

To rule out issues related to the playback location take take the VCR a few miles away and play the tape. If the noise is still present it would strongly indicate it is the VCR interacting with the tape content.

That description sounds like my test file, not Barry's.

Barry's helicopter sound is in a much lower band, maybe 500 Hz max, of ten pulses per second. See them highlighted in blue my RX display image.

Also in Barry's file, there are some weakish tones visible between 2kHz and 3 kHz (continuous straight horizontal lines ) but that's not sound we associate with helicopters. Probably just the interference we often hear in many VCR's on linear audio, and generated internally by the VCR itself.

[BarryTheCrab]

I find this back-and-forth analysis discussion very interesting and I get wide eyed as I read you smarties try and dissect the noise.

[timtape]

It's all fun Barry!

Is this the helicopter sound you were talking about? I've tried to filter out the party sounds.

Cheers Tim

[qwertz73]

I don't know if this can help and if the problem is the same as yours. I have a ground loop problem when the audio output is connected directly to the video capture card or to an external USB audio card.

I've solved the problem by plugging in a USB adapter that eliminates this mass loop.

I've attached two audio excerpts

iFi Audio iDefender+_1.jpg

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iFi Audio iDefender+_2.jpg