Atem Mini HDMI Audio "too hot"

Hi,

I have been scratching my head over the following audio issue:

In the following setup, with Microphone, SD MixPre 3 II, GH5 and Atem Mini, I would like to route audio through the camera for purposes of synced audio.

See also the attached png as a diagram.



My issue is that even with Stereo Out gain on the Mix Pre set to -40db, and -12dB at the camera, the audio seems to arrive way "too hot" at the Atem Mini.

The crazy thing is: the audio is fine at the camera up to the moment I attach the HDMI connection from camera to Atem Mini. Once HDMI is connected, the levels are very high and there is a hum and lots of crackling.

What have I tried so far: Ground loop? Put camera on batteries (unplug dummy battery), unplugged MixPre, ran on battery, only connection left is Atem Mini to PC via USB-C. Still buzzing / hot audio. The crazy thing is that this even happens with an Atem unconnected to ac power (but connected to USB-C). Put PC on different power socket. Used different USB-C input on PC.


I have swapped all HDMI cables, USB-C cables etc. to no effect. Routed audio through a different camera (the V777 camcorder), same result.

Any ideas? I have a working solution by connecting the audio into the Atem Mini, setting Mic 1 to line level and adding the required delay, but would prefer the routing through camera option as I won't have to work out the right delay every time I change to a different camera type.

The issue is you are feeding a line level 500 ohm unbalanced signal into a mic input. A mic level signal is a (-36 dBu) 100k signal, and this is what the camera expects. The MixPre 3 output is an unbalanced, 500 ohm output impedance, at +7.8 dBu max output level. So you are feed a line level (hot) signal to to a camera Mic input, which expects a lower level signal.

You best solution is to just feed the MixPre line output to the ATEM Mini aux stereo line input, then your impedance and signal levels will match. You can set the aux audio inputs to Mic or Line in the setup/control software mixer Tab. First, you need to update the ATEM Mini to the new FW release, which adds audio delay to the aux audio inputs to get the audio inputs sync’d with the video inputs.

I tested this with the MixPre D, works quite well. If you need a mixer to feed several mics to a camera, then the MixPreD is better, because it has a stereo Mic level, unbalanced stereo 3.5mm output available, to connect directly into cameras which only have mic level inputs. The Balanced outs can be set to Mic or Line level. The lack of an unbalanced mic level out on the MicPre 3 has kept me from upgrading to one. I need the unbalanced mic out.
Cheers
Cheers

Hi Danny,

Thanks for the quick and comprehensive answer! I got it working with routing the audio to Atem Line in.

What I still fail to understand is that it works fine when not using the Atem in the chain.

This tutorial video from Curtis Judd

worked perfectly for me. In-camera audio is fine when it comes from the mixpre. But as soon as I connect camera HDMI to the Atem everything turns into a distorted mess.

I have a solution by routing it differently, but this still bugs me from a scientific perspective.

Best wishes,

David


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It appears the GH5 is dealing with the hot input, until it has to pass the signal through. Have you tried recording this audio setup on the camera, then checked out how the audio sounds? Chances are it will be distorted there also. If you are monitoring the audio via the camera, you may not be hearing the full actual processed signal, but just the mic input coming into the camera, which may sound OK there. But what you are hearing from the audio in the camera’s HDMI is list princesses audio, and reflects what is actual going on.
Cheers

It appears the GH5 is dealing with the hot input, until it has to pass the signal through. Have you tried recording this audio setup on the camera, then checked out how the audio sounds? [...]

Hi Denny, yes I have tried this now.

https://vimeo.com/431020216/58753e669c

The video in this link shows the phenomenon "in action". This is the recorded in-camera audio (fine), then HDMI is connected, and it's all messed up. I have reduced the levels in the "messy" bit so it doesn't blow out your speakers / headphones.

Why would connecting HDMI cause this?

Thanks and best regards,

David

What cable do you have connecting the mixpre to the GH5? It's fairly common on bal/unbal connectors to send the cold leg to ground. On a TRS or TRRS you may be picking up that signal from the HDMI shield.

Good Luck

Hi, thanks for the post, I have tried two different, bog standard, aux cables 3.5mm to 3.5mm jack.
Something like this: https://amzn.to/2YTxc0v

I already swapped this against another AUX cable. Same result. Should I be using something else?

Thanks again,

David

[Gary Adams]

As this is interesting I wonder if the CEC camera controls are affecting the camera adversely. I would try using an HDMI splitter from the camera and feed Output 2 to the MIni. That will block any external controls.

Regards. Gary

So I'm going to have to work for it? Sounds broken but....

The manual states the output levels may change when using HDMI, that shouldn't have any impact on recording unless there is a bug, which there may be. In theory there could be an output change, that's expected when plugging in HDMI, it doesn't mean it should necessarily be garbage, only the camera switches modes from real to rec.

duck.png (65.15 KiB) Viewed 6043 times

I'm guessing the audio isn't corrupted in the MixPre. What happens if you plug the GH5 into a monitor?

I'd try some other devices to see how they respond and definitely do some snooping on the grounds. The only thing that makes sense is that you're getting juice on the ground from the HDMI cable. Do you have a meter?

Good Luck

Hi, I have a standard multimeter, but wouldn't know how to use this with HDMI. I guess it may be a ground, indeed. But I have very little I can still disconnect in order to remove the ground:

I already tried the Mixpre and the GH5 with Battery power, and the USB C to the PC is necessary for basic functionality

I think your audio signal is using the wrong ground. It's using the HDMI for ground and it's causing an impedance issue. Ensure the camera's DC is grounded better. Check for continutity between chassis, cable shields, S of TRS, and DC-. If there is a break in continuity you can check the voltage when/if the HDMI completes the circuit. Have you wiggled the jack? Perhaps a loose solder presents HDMI ground a path of lesser resistance.

I'm inclined to believe that the Atem mini HDMI and chassis are not common. The output of the MixPre is now pushing down the aux shield and the HDMI shield, the impedance difference is manifest as noise and gain. You could short the DC- and the HDMI shield on the Atem and I've fixed your problem or destroyed your switcher, what does the meter say?

Nonestly this is all wild speculation, thanks for letting me have some fun at your expense.

Good Luck

I think your audio signal is using the wrong ground. Ensure the camera's DC is grounded better.

Hi, will try that and will also try to use a usb c isolator (coming in the mail tomorrow).

When you say better ground for camera DC: the problem also arises when on battery power, so it’s not running to a DC dummy battery. I’ll still meter it, but I thought by running on battery I already removed one source of error ...

Thanks for helping out, Howard!


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Check for continutity between chassis, cable shields, S of TRS, and DC-. If there is a break in continuity you can check the voltage when/if the HDMI completes the circuit.

Here are my readings

just to make sure, without AUX and HDMI cable, no continuity whatsoever between camera chassis or any other contact point and Atem. Expected behaviour.

Continuity between

- camera chassis (I'm using the bare metal strap holders as contact points) to internal HDMI shield: continuity (meter beeps),
- Chassis to TRS Sleeve: continuity
- Chassis DC -: continuity
- also continuity between DC- and HDMI shield, DC- and TRS Sleeve in all permutations.

- there is no continuity between DC- and the Atem HDMI Shield.

Add the AUX cable from MixPre:

we now have continuity between DC- (and the other contact points) and Atem HDMI Shield (any of the ports in fact) when connecting the HDMI cable[/b], Voltage readout 200mV

Add the HDMI cable, still continuity, but voltage drops to around 10mV.
Impedance also drops significantly.

When removing the USB-C Connection from the Atem to PC, no continuity. Maybe I'm getting a ground loop as the MixPre is connected to the same PC via USB-C as the Atem Mini?

Howard, do the measurements help in your analysis? Thanks so much in advance.

David

That, I think is the source of your issue, you Dudu not mention the do pi was linked to both devices. Try disconnecting the USB from the lab top and have the camera mixpe and Mini only connected. How is the audio with this setup, also try disconnecting the MixPre from the computer, and test the basic free standing setup. Then add the other connections back in, one at a time, testing with each connection.
Cheers

Ok, I'm now actively losing the will to live.

I have removed the MixPre from the USB of the computer, and things are still the same.
That being the case, introducing a USB ground eliminator https://ifi-audio.com/products/idefender3-0/ and separate Power injection (to avoid USB power) between MixPre and the PC did not work either.

I can basically get the noise phenomenon even with the barest of setups:

Microphone to MixPre, which is connected to a battery powered GH5 -> Audio fine, then connect HDMI to a POWERED OFF Atem Mini (but connected via USB to the PC).

That's it - throwing in the towel - looks like I'll go to my grave wondering what this is all about

Usb-c??? Disconnect that system entirely. It's probably a good idea to disconnect a display as well as that can be a source if interference.

When you say plug in the Aux cable and get continuity (this IS a ground loop) you must have something connected, that is the usb cable or something else?

Check continuity between the shields of the Atem the same way you checked the camera. They should all be tied together, if they are floating then that is going to explain your impedance issue.

I can't imagine why the grounds would be isolated, it should be on the Atem like it is on the camera. I'm sure if you check the MixPre chassis, trS, dc-, and xlr pin 1 they are common as well. Currently the floating grounds are looping through the camera.

If I was going to take another guess it would be that the Atem TRS input sleeve IS common with the DC-.

Good Luck

Usb-c??? Disconnect that system entirely.

Well, the Atem Mini won’t work if not connected to USB C and I have already disconnected the Mixpre usb c from the PC and replaced with independent power source.

I’ll try some more measurements as you suggested. Once I’m less worked up .

Thanks for your continued help! Really appreciated!


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Hi,

I've been following this conversation in anticipation of what I'll be trying to solve once my mini pro arrives. I will be using it for a classical music live stream, where audio quality is very important. Ideally, I'd like to connect a mixer or audio interface into the mic inputs on the atem.

I haven't yet settled on a mixer/interface, but wanted to see if any of you have any recommendations or examples that have worked without issue. Thanks for the input.

Coming back to this one after trying a couple of variations and use cases to wrap this up and probably help others avoid hair-loss

Findings:

- Recording audio for video from the Mixpre into GH5 works flawlessly with the settings from the video above, there is also a PDF from sound devices that explains the process incl timecode.

- Bringing the Atem Mini into the mix does *not* work when trying to route audio through the camera - noise as described per this thread

- Three working solutions up to now:

1) route audio from mixpre through mic in (set to line level in Atem Software Control) and add around five frames of audio delay.

2) use a line-level capable camera to begin with (BMPCC4k, GH5s etc)

3) cheapest but you lose the extra audio recording / processing capability in the loop: remove Mixpre, run mic straight into camera, and from there on into Atem. Ok choice for live streaming if onboard mic preamps deliver acceptable quality.

Thank you to everyone who accompanied me on my learning journey

David


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[Gary Adams]

I have probably stated this in other posts, but it's worth repeating. The ATEM Mini 3.5mm inputs are Unbalanced Stereo switchable from PC type Microphone levels at -55 and HiFi Line levels at -10. I recommend feeding a HiFi level rather than a Microphone level if at all possible for the best quality. What I strongly recommend is having a good transformer isolation box handy even if you find it is not necessary for your setup. There are inexpensive and more expensive versions form about $10 to $100. I have been playing with both and find them quite useful in eliminating any ground loop or noise from the wiring. Frequency response is generally very good and there is little risk of distortion. The more expensive versions will also convert balanced to unbalanced perfectly. Doing this with a cable usually does not work very well. I hope this helps. Stay safe everyone.

Regards, Gary

What I strongly recommend is having a good transformer isolation box handy even if you find it is not necessary for your setup. There are inexpensive and more expensive versions form about $10 to $100.

Hi Gary, thank you! Any buying recommendations?


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