Avoiding echo and feedback with in-theatre zoom calls

[Derek Martin]

Hi,

Does anyone have advice on avoiding feedback when having a zoom call onscreen? We've experimented with both a laptop and a cell-phone in the cinema to take audience questions, with the booth running it off another laptop, but without much luck.

thank you,

Derek

[Marco Giustini]

I think the best solution would be to mute the call/mikes alternatively. When the audience talks, the call is muted, when the person on the other ends speaks, the mikes are muted.

[Hong Sung Hyeok]

The key is to prevent the voice sound output from the speakers from being picked up again by the microphone.
high-performance directional microphone and the speaker's position seem to be crucial.
It might be a good idea to switch the audio output from the screen speakers to the surround speakers, depending on the situation.

[Steve Guttag]

Proper Zoom/Team systems employ Acoustic Echo Cancellers. If you've ever stood in a room with someone and talked on your cell phones, you quickly realize there is a notable delay. The same holds true on a zoom call. A system like Q-SYS uses AEC to mitigate the echo problem.

Here is a video from Q-SYS on how theirs works:

Part A:

https://youtu.be/-ADwIRXJGCc?si=-U-WjU1IY5EFT1zQ

Part B:

https://youtu.be/k2Hq_VOK3ac?si=8FuSaxMhJQGLmwLv

If nothing else, these should give you an idea of the problem and a solution to the problem.

[Harold Hallikainen]

I've also used a microphone with a Push To Talk switch that mutes the speakers when pushed. This worked well, but I tended to talk over people since I could not hear them...

[Jim Cassedy]

<edited> Proper Zoom/Team systems employ Acoustic Echo Cancellers.

As Steve points out, one of the better ways of doing this is to have a complete
echo cancelling system. One of the worst shows I've ever done in my life was a last
minute two-way zoom type QnA session with a well known cinematographer, that
I just wanted to die after. (and none of it was really my fault)

On the other hand, one of the best 2way sessions I've done was a set up at
a high school for a political event with former president Obama on the other end.
But for that show, 'money was no object' and we had hired a whole rack-full of extra
equipment to make sure it's done right.

Fortunately, ZOOM audio and echo cancelling has improved greatly over the past two
years, however, whenever I'm called on to do one of these events where they insist on
2-way audio, I have my own 'bag of tricks' and here's what I've found works best for me:

1) An older, but not ancient, Windows laptop, with an audio card that has discrete
Audio IN and Audio OUT jacks. ( I have an older DELL I use for this)
2) An NEC AEC-400 echo canceller. I became very familiar with these while working
with high-end video conferencing systems almost 20 years ago. What I liked about
them, aside from their excellent performance, is that they have XLR connections, and
there's also line level outputs as well as a real 600Ω 4-wire hybrid in/out connections
that were designed for direct connection to a phone network, but can also be used for
standard audio with adapters. It even has a small built in amplifier to drive a speaker
if desired. These things originally cost over $1000us back-in-the-day, but can often
be found on e-bay for $100 or less. (I paid $50 for mine about 2 years ago)
Another unit I've used that I've used and also works well is a GENTNER audio echo
canceller, which also show up from time-to-time on E-bay.

Also, as pointed out in an earler post, local microphone/speaker placement and room
acoustics can also play a big part in how well things sound. And, unfortunately, no
matter what you do on your end, you are at the mercy of conditions and equipment
at the other end of your connection, which can cause you problems. Fortunately,
I don't have to do too many of these any more, but when I do, the NEC usually works
well for me. I got very experienced with these when installing high-end video
conferencing systems in corporate board rooms, so I got good at getting them to
work, but they can be a little intimidating to set up if you're not familiar with them or
don't have access to a manual. ( I'm not sure you can still find manuals online)


(Online Photo of an NEC AEC-400 Echo Canceller)
NEC-AEC400.jpg

[Ryan Gallagher]

In our mixed use venue we do this pretty regularly. Believe it or not sometimes the minimal effort/complexity version is the best with zoom.

We've had luck having the presenter/meeting laptop using it's own mic for the call audio, AND to hear the audience questions. Although last time we didn't have QA mics and the remote person was still able to hear the audience questions just fine (I was shocked). We just take the laptop audio feed for the house and because of some of the smarts in the zoom audio management, it handled it pretty well without feedback issues.



That said, in past industry jobs I have been a Zoom Operator for much much higher profile corporate events. CEOs and keynotes and the like. AMD, Dell, etc. But in a "built on site video village" type gig. Not with the help of permanent infrastructure like QSYS.

In that world they throw more hardware and personnel at the task, especially if they want to feed camera switched video to the remote guest. But on the audio side from memory...

Usually there is a machine that hosts the meeting, deals with waiting room, guests, chat etc. If there is more than one remote guest you have to manage their mutes for them too.

Another machine is dedicated to getting the remote video onto a dedicated output without decoration for the live room. If you want to avoid the tile view and live-switch between guests you'll potentially add another laptop for each desired full screen slot (the desired or switched room video is fed via a capture device to the guest, sometimes it will be a view of the moderator, sometimes the audience, or live switched etc).

A separate machine joins the meeting dedicated to audio (although it is possible to combine it with the video machine), it typically would have a small USB mixer/inferface. The live mic of the moderator can be fed to the meeting that way and solo'd by the operator etc. If there are other mixes to send the remote guest you have a few more inputs available via the little mixer, greeter talkback for example (plus whatever the person running local room audio is doing to control your upstream mixes). The mini mixer also acts as that laptop's audio/meeting output, and in this mode it's wise to turn off all zoom's audio processing/muting on the local side, cause you are sending it a relatively clean signal from a vocal mic, just let the remote guest hear everything when that mic is hot).

Aside on the video subject, zoom has some NDI support too, and there are some clever ways to reduce the hardware required to get clean video feeds from it.

An especially high profile remote guest would warrant backups/redundancy of the various elements too. Or they may have other stupid complication demands, like a professionally done chroma key and background on the remote guest's video (although zoom does that pretty well now if they are equipped to set it up on their end).

[Ryan Gallagher]

I should add that the "simple" method above may only work for us cause in those situations our speaker is through a separate live PA, and not coming from the screen channels above and behind them.

If using the simple method it's important to start the meeting, test, and configure the extended desktop for undecorated speaker window during checkout. The laptop is then left setup that way and carried onstage without having to plug it in live. If the speaker won't be joining until closer to the end of the film, test with another account, and ideally have an aux or split of the extended display visible offstage so that the meeting configuration can be tweaked/tested if need be during the film as the remote guest joins. Interacting with the screen as the 2nd display is pretty difficult from that close up.

[Carsten Kurz]

Shouldn't a ducker be a solution? Mute audience mics whenever the remote audio has active audio. Also, audience will mostly not talk interactively - it should be possible to enable the audience mic(s) with the space-bar mute/unmute through an operator.