[Richard Crowley]

[Tom Galli] “They’re designed to eliminate ambient noise, not noise in the signal.”
Yes, that is true. But remember that WHILE YOU ARE RECORDING:

THE NOISE “IN THE SIGNAL” IS THE SAME AS THE “AMBIENT NOISE”.

That is because noise-cancelling headphones were designed for the purpose of PLAYBACK of PRE-RECORDED audio in the presence of LISTENING-ENVIRONMENT noise. When you use them to monitor WHILE RECORDING, they will LIE to you by removing the background noise so that you are not aware that you are recording it. THAT is the major reason why it is a bad idea.

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Recording audio without metering and monitoring is exactly like framing and focusing without looking at the viewfinder.

[Richard Crowley]

Perhaps not relevant to this original situation, but…..

Last week I watched on YouTube several episodes of a TV series featuring James May on the topic of children’s toys from our earlier lives. Here are some examples:
https://www.youtube.com/watch?v=y19b0KCFiVc
https://www.youtube.com/watch?v=MHbPFhZKOF8
https://www.youtube.com/watch?v=K-xsAIvx9XQ&list=PLDAceOw8D4EgJSoTyNLw64NuElAw1tEr6

There were several places in the various shows where there were ambient sound and/or music at above-average levels, and they just buried the dialog. When I looked at the YouTube comments, there were MANY complaints from ordinary viewers (not apparently production professionals) about the sound mix.

There was one response from the person/organization who uploaded the video to YouTube. They stated (guessed?) that when they created the YT video, they mistakenly included the effects and music stems IN ADDITION to the full-mix. So that, essentially, the effects and music stems were added into the mix TWICE (+3dB). And I believe that is exactly what I was hearing. At least it sounded convincing to me.

But I have personally experienced the problem of the mix sounding fine in the control room, but unsuitable for the system/acoustics where it was to be deployed.

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Recording audio without metering and monitoring is exactly like framing and focusing without looking at the viewfinder.

[Richard Crowley]

[Tom Galli] “”is it in the mix, or just in my ears?””

THAT is the reason to NOT use “noise-cancelling” or any other consumer-scheme technology when doing serious professional work.

Noise-cancelling headphones WILL reduce/remove ambient repetitive noise from what you hear in the headphones. Unfortunately, that INCLUDES reducing/removing the ambient noise that you are RECORDING. So you don’t know (until it is WAY too late and too expensive) that the generator (or the airport or the interstate highway, etc) was a problem that you didn’t hear on location.

That reduces your professional talent to that of a rank amateur who doesn’t even think about ambient noise because they have no experience understanding how microphones work (vs your ear/brain system) when it comes to rejecting ambient noise. If you have tricked yourself into not hearing potential problems, then you can’t deal with them properly. And presumably getting good, clean dialog recording on location is why they are paying you.

As you have surmised, the generator is another self-imposed problem (like using noise-cancelling headphones) which is easy (but not necessarily fast or cheap) to mitigate.

If you have not already encountered it, highly recommend this document which you should read and share with your producer/director/AD, etc.

https://filmsound.org/production-sound/openletter.htm

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Recording audio without metering and monitoring is exactly like framing and focusing without looking at the viewfinder.

[Richard Crowley]

The traditional US terminology is a male “Plug” and a female “Jack” However in UK/EU they seem to commonly use the term “jack-plug” which is very confusing to us on our side of the Pond.

But, to answer your question. My favorite source of bulk cable and connectors is an online dealer:
https://www.redco.com I have made almost all my own cables for many decades, and Redco is my preferred source for both cable and connectors. They have a very wide varety of 3.5mm (male) plugs which would be suitable for headphone cord replacement:
https://www.redco.com/Mini-3-5mm-2-5mm-Connectors/
Note that there are also 2.5mm connectors on that page, so be sure to get the right size!

I prefer to use “right-angle” plugs, especially on 3.5mm headphone cords. Because the plug is so mechanically vulnerable, using a right-angle version greatly reduces the torque on the shaft of the plug when the cord in under tension.

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Recording audio without metering and monitoring is exactly like framing and focusing without looking at the viewfinder.

[Richard Crowley]

Perhaps more appropriate to use a “gate” sometimes referred to as a “noise gate” because that is a very common use of the gating function. You can set the threshold to some level just below the dialog but higher than the noise.

Note that you can have the spaces between the dialog completely blanked out to complete silence. However, that typically sounds unnatural. So it is common practice to allow an attenuated level of noise through for a more “natural” effect.

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Recording audio without metering and monitoring is exactly like framing and focusing without looking at the viewfinder.

[Richard Crowley]

[Ángel Molina López] “does this affect video playback or audio quality in any way?”
No, not at all.

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Recording audio without metering and monitoring is exactly like framing and focusing without looking at the viewfinder.

[Richard Crowley]

if you can’t get the computer to route the audio to both places, then you will have to “tap” the audio from the HDMI connection via the “Audio Extractor Converter” gadget previously suggested.

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Recording audio without metering and monitoring is exactly like framing and focusing without looking at the viewfinder.

[Richard Crowley]

It is not clear what is the source of the program material. Is it streaming (or playback) video coming from your computer?
Since you did not identify your computer, either, we don’t know what options may be available from your computer operating system? PC? Mac? Linux? Can you enable both the HDMI sound output AND the headphone (or audio interface) to operate at the same time?
If not, then you may need to extract the audio from the HDMI stream with a small inexpensive hardware gadget like this: https://www.amazon.com/dp/B00BIQER0E (or a dozen very similar gadgets).
Some of those gadgets may have 3.5mm TRS jacks to directly connect headphones. But you may need an additional headphone amplifier to control and/or boost the headphone volume.
If the HDMI video/audio source is coming from your computer, it is not clear what part your Komplete Audio 6 USB interface would play?

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Recording audio without metering and monitoring is exactly like framing and focusing without looking at the viewfinder.

[Richard Crowley]

Yes, an omnidirectional mic hung strategically above the center of the table would seem like the simplest and easiest solution. BUT, as you say, both room acoustics (reflections, echo, etc.) and ambient noise (internal HVAC, external traffic, etc.) are significant factors.
The more echoey the space, the more reflections from table-top, walls, etc, the lower quality of the speech. And likewise, the more noisy the space (whether internal or external), the less intelligible will be the dialog.
If you had a big budget, then you would put a mic on each participant and use an auto-mixer to open each microphone as the participant speaks. A headset mic would be much better than a clip-on lav mic on the collar, etc.
So, following the rule “Quality/Speed/Cost, chose any TWO”, it would be good to experiment with the hardware you can afford in the space designated to see how close you are to the desired level of audio quality.

Now, doing a two-way production interactively with other(s) at the other end of the party-line raises the stakes significantly. It was not clear whether you are asking about taking turns during designated time slots, or whether you are actively gaming with other team(s) concurrently. If you are only taking turns, then it doesn’t present any particular problems.
But if you are interacting with others online in real-time that requires echo-cancellation and other sophisticated signal processing.
This kind of automatic switching and echo-cancellation is done in online communication applications like Skype and Zoom and Hangouts, etc. If each site was called into a Zoom conference, that would handle the automatic switching and echo-cancellation that you need. Zoom (or any of the others) don’t know or care if the end-point is an individual or a group of people with multiple microphones and a mixer, etc.
Of course, you would also need to experiment with where you put the speaker so that the participants can hear the other end of the conversation. Perhaps also flying it overhead above the microphone. But guaranteed it will not work without the “conferencing magic” provided by the conferencing services.

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Recording audio without metering and monitoring is exactly like framing and focusing without looking at the viewfinder.

[Richard Crowley]

When recording larger choral groups, especially where they are standing in multiple rows, we typically rig the microphones higher, usually over the head-height of the first row. This gets a better coverage of the entire group vs. the proximity effect from the front row.

However, for a group all at the same height, on the floor, whether in a row or in a circle, then head-height is typically sufficient.

But note that the acoustics of the space are also a very large factor in deciding where to place the microphone(s). Larger choirs, like orchestras and pipe organs, are more dependent on the acoustic space around them. So mic placement is always a “season to taste” trade off experimental decision. We try to leave enough time to move microphones around during rehearsal to see which location sounds the best. There is no hard and fast rule.

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Recording audio without metering and monitoring is exactly like framing and focusing without looking at the viewfinder.