AC mains related image noise during analog captures?

[aramkolt]

Hello all,

I'm wondering if it is well documented that AC mains EMI affects analog captures significantly enough for it to be easily noticeable and worth doing something about, or if it is usually super subtle and barely perceptible if at all?

I feel like if it was a common issue and could improve capture quality that it would be discussed more as part of an essential capture setup and deemed just as necessary as a good capture card for example.

I've heard of a few different recommendations as far as power conditioners and backup battery systems go - I've seen Lordsmurf recommend Cyberpower UPSs' - namely the 1500VA/1000W model if I recall correctly.

I'm not clear if those UPS's filters are anything special or if it is more the backup battery in case of a power outage that makes them recommended though as it could save you from having to do a recapture if you're in the middle of one and there's a power outage. My understanding is that the pure sine wave inverter only kicks on if there's a severe voltage drop - say below 100VAC. It does do active line monitoring to up or down regulate the AC mains if it gets far enough out of spec, but again, I don't think that does anything for AC mains EMI (electromagnetic interference)

Also wondering if there's any point in using something like the ISOlator series of isolation transformers from Tripp lite for example which do both filtering and separation of neutral from ground.

Greenwave also makes some relatively inexpensive line filters which are essentially just big AC capacitors wired in parallel to hot and neutral which do produce measurable reductions in mains EMI - though their target audience seems to be those that are psychologically affected by EMI rather than those that want to reduce analog audio/video interference related noise.

I'd be curious to know if anyone has personal experience with a big improvement observed in their captures when using various EMI noise filters (like Greenwave's), power conditioners, or isolation transformers.

Lastly - sort of related - I know ground loops can cause some audio noise/hum, but I am unsure if ground loops can also affect analog video and what the way around that would be if so.

[themaster1]

for your info: https://www.avartifactatlas.com/artifacts/ac_beat.html
ground loop can affect video in the form of a continuous rolling up horizontal bar (can be barely noticeable yet very present), and can go up to Sync issues (very noticeable). One of my vcr is suffering from that (i've checked chassis ground).

solutions: https://www.sct.com.tw/articles/4-ef...o-interference

Trying to find the right solution myself

[aramkolt]

Hmm. I am aware of the audio isolation transformers that break audio ground loops, but hadn't heard of them for video. Not sure if it can be done with S-Video?

Another idea would be to convert the analog signal to digital at the VCR before it's transmitted to the capture card either with an optical cable or possibly in the form of digital coaxial. Issue there is that the Analog to digital converter used could add some noise of its own.

I did notice that the recommended TBSC sound card does have a "Digital CD Audio In" that is two pins on the inside - I'm wondering if that is essentially digital coax in. If that were to be the case, you might be able to convert the analog very close to the VCR and possibly not pick up any noise along the length of the audio cables. Whatever is used to convert to digital could introduce its own noise though.

For audio, it doesn't look too complicated to use something like an optoisolator as an alternative to transformer-based ground loop isolators which may invert or cause some mild distortion, but I am unaware of a prebuilt solution based around an optocoupler which would also electrically isolate the audio signal, but here's an example circuit:
https://learnabout-electronics.org/Semiconductors/opto_53.php

Still would be curious to hear about any results others may have had using commercial AC isolation transformers that don't actually electrically isolate neutral from ground, but they are supposed to be more for electrical noise isolation I believe. These would be products like the Tripp lite ISOlator series or any sort of medical isolation transformer which I believe are used to keep mains noise out of EMI sensitive devices such as EKG machines.