Does ‘echo cancellation’ do anything dire to the audio? I’m audience only in case that affects anything.
It just cuts instruments out, so audience hears muffled sound instead of nice and crisp
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If you are muted which, as an audience member, you should be, echo cancellation does nothing.
If you do have your mic enabled, echo cancellation will try to prevent your speakers feeding back to your microphone.
If you are in a low-latency situation, this causes, well, “feedback” usually in the form of a loud squealing tone. But online communication is never “low latency” so, in this case, it acts like a delay pedal and produces a series of echos which is very disruptive.
To prevent this, algorithms will try to identify and cancel out the sound from your speakers. This is never perfect and will always result in audible distortion, and is best avoided.
The way to avoid it is to use headphones so the sound from the speakers doesn’t get to the microphone. Then you can normally turn off echo cancellation.
Note that Bluetooth headphones/ear buds will create additional delay.
The very worst situation tends to be where you are using the laptop speakers and microphone, as the speakers and microphone are very close to each other and usually not very good quality.
A reminder: this only applies to people actively using their microphone in the Zoom call. In the case of an OM, this usually means the performer, MC, etc.
If you are an audience member, you should have your mic off and it will not impact you.
Cheers,
Keith
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Just typed my “quick point” below and it wasn’t so quick! 
Therefore I thought a quick summary at the top might be handy:
Echo, when in reference to Zoom, is when other’s hear their own voice back after it has come out your speakers and back into your microphone. Echo cancellation in Zoom (and other videoconference apps) aims to prevent that.
- Echo cancellation should always be enabled if you are using speakers which can be heard by your microphone and you intend to unmute whilst others speak during a Zoom meeting.
- Echo cancellation in Zoom’s world intends to cancel out other people’s audio, not your own, when sending audio back to others.
- Zoom’s Echo cancellation may impact your sound when enabled if other people make noise whilst you’re trying to be heard as it will subtract their noise from your audio when sending it back out, therefore sometimes making your audio sound thin or possibly even ducked out completely.
- If you’re always muted when other’s talk or your mic can’t hear your speakers (e.g. you’re listening through headphones) then echo cancellation isn’t required (although Zoom’s EC does tend to boost your audio and add some EQ when it’s enabled & original sound is not enabled, which can be useful at times
).
Therefore, my recommendation for OMs is to:
- Use headphones if you can (so you can disable echo cancellation in Zoom, if you wish).
- If you have to (or prefer to) use “open” speakers, then you need to have EC enabled (otherwise you will need to constantly unmute then re-mute, each time you have to speak, so as not to impact others when they talk).
- Always try to mute regardless when you’re not speaking, as that is good practice anyway
(my original message - feel free to ignore 
)
Just thought I’d make a small point of clarification with regards to Zoom’s use of Echo Cancellation. Yes, Zoom is processing what your microphone is picking up from your speakers, but only in relation to what it receives from others online, i.e. the purpose is to cancel out other people’s audio so they don’t hear their own voices back from you when they speak. As Keith mentioned, Zoom - and other similar videoconference apps - apply an algorithm to subtract the incoming audio from your audio when sending it back out to others. Understandably, this can be difficult at times, depending on various factors, so it’s not always perfect, but 1000 times better than it use to be 10-15 years ago - oh man the apps back then sucked at that! 
).
As such, if you have it disabled and you are “echoing” other people’s audio back to them, typically you don’t realise there is an issue as you won’t hear the echo (i.e. their audio goes from your speakers into your mic and sends it back to them along with any audio from you, so they hear themselves echoed back but you don’t). Therefore, conversely, if you hear an echo of your own voice on a Zoom call, then it’s typically not a problem with your setup but someone else’s. Look for who’s image lights up when you hear your voice come back and it will be that person who’s listening through speakers with echo cancellation disabled
With regards to the term “feedback” in the videoconference world, we tend to refer to “feedback” (i.e. that high pitched squealing noise as opposed to an echo a voice) when it happens as a result of two people connecting to the same Zoom meeting within earshot of each other, so audio goes into the mic of one device then out the speakers of the other then into the mic of the original and then out the other and over and over again… looping super fast until it quickly results in a very unpleasant high pitched squeal! 
This commonly occurs in conferencing rooms which have a built-in VC system, then someone wants to share from their laptop so they join the same meeting but don’t disable their audio and then immediately there is horrible feedback that occurs Thankfully this is getting less common these days due to people becoming more saavy to this and Zoom (for instance) being smart enough to detect that issue and auto-disabling audio on the offending device 
So the point here is that, Zoom’s EC won’t do anything to resolve any local feedback you are getting within your own audio setup, it is specifically there to prevent you from echoing others back to themselves.
So not sure if any of this is useful, or just makes it more confusing! But what I really wanted to point out is that echo cancellation in Zoom should always be enabled unless you’ll always be muted or your mic can’t hear your speakers
As to whether Zoom’s EC causes any negative impact when enabled whilst Original Sound is on, I can’t say for sure. I know Zoom’s EC does do more audio processing than just cancelling out far-end audio when enabled without OS on (as mentioned above it definitely adds a boost and some EQ) but even if it doesn’t do that with OS on then it will certainly impact your audio if other people make noise whilst you’re playing and that’s picked up by your mic (because their audio will attempt to be subtracted from yours, and the subtraction won’t be perfect). But outside of that, I’m not sure that it does cause problems when Original Sound is turned on, or at least I haven’t really noticed anything significant 
Just a note on when original sound sometimes turns itself off after your have turned it on in a meeting, it’s worth noting that if you toggle mic inputs in Zoom at any point, it will disable OS so that you’ll have to turn it back on again, perhaps this might explain some occasions where it has occurred. Although, I do feel that it has happened randomly at times as well… 
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