OBS recorded audio distorted

[KenMitchell92]

I am trying to set up OBS to record our church service and output a NDI feed to be used in other portions of the church. The setup is really simple. We are feeding audio from a Midas M32 Aux Outs (stereo) to the Line In of a PTZ Optics camera. We have OBS installed on a MAC computer with the NDI plugin installed. MAC computer and camera are connected to the local network via ethernet. The NDI source is the only input source for OBS. The problem is the audio has a static sound in it along with the sound board audio. My impression is it sounds as though the input audio level is too high and is clipping, but the OBS audio level is set to stay in the green with only occsional peaks in the yellow.
We also have a Pro Convert NDI to HDMI encoder connected to the network and the HDMI output going to a TV. The encoder is set to the NDI feed coming directly from the camera. Video and audio on the TV are good. No distortion and sound level is good.
According to the Midas 32 specs, the nominal level at the Aux Out outputs is +4 dbu (1.228 Vrms). Nominal Line In level is -10 dbV (.316 Vrms). Could we be overdriving the camera Line In input causing the audio in the camera NDI feed to be clipped? Do we need an attenuator between the Aux Outs and the Line In to drop the level? Doesn't make sense to me because the audio is fine at the TV using the same NDI feed that goes to OBS. I have been able to make other recordings using different audio inputs (media for example) and the audio is fine in the recording.
I'm not a sound engineer and this is my first time using OBS, a sound board, and camera together. Can anyone help me understand what's going on here and how I can correct it?

 

[AaronD]

According to the Midas 32 specs, the nominal level at the Aux Out outputs is +4 dbu (1.228 Vrms). Nominal Line In level is -10 dbV (.316 Vrms). Could we be overdriving the camera Line In input causing the audio in the camera NDI feed to be clipped?

Yes. That's an 11dB difference in the expected level, with the console being higher. 0dBFS on the console overdrives the line-in by 11dB. Set a limiter on the console so that it never EVER exceeds -12dBFS at the actual output.

I have an X32 in a church rig (identical to an M32, but with cheaper preamps and a flat control panel), and if I remember correctly, I have its final limiter (standard compressor on a matrix) set to -22dBFS threshold, ratio all the way up, instant attack, and no makeup gain. Then the fader is all the way up (+10dB) so that it can't go any higher by accident. -22dBFS limit + 10dB fader = -12dBFS maximum output, which the consumer line-in sees as -1dBFS.

Lock those settings in, and tweak the others - knee, hold, release, and all of the preceding processing including the mix level that goes into this final limiter - so that it sounds "right".

(Considering the mix level that goes into a -22dBFS limiter, don't worry about dropping into the noise floor by mixing that low. It's floating-point all the way through, so unless you really egregiously abuse it, the noise floor actually follows the audio level. It's not fixed like it is in analog, or integer digital. And it's 40 bits, when the 24-bit converters are already far better than analog could ever hope for. So the internal noise floor is so far down that the entire system is effectively perfect analog to analog, no matter what you do in between.)

Do we need an attenuator between the Aux Outs and the Line In to drop the level?

Not if you limit it in the board like that. If you want to have a physical attenuator so that full-scale = full-scale on both sides, that's fine too. Just tweak the threshold above by the amount of that attenuation.

Doesn't make sense to me because the audio is fine at the TV using the same NDI feed that goes to OBS. I have been able to make other recordings using different audio inputs (media for example) and the audio is fine in the recording.
I'm not a sound engineer and this is my first time using OBS, a sound board, and camera together. Can anyone help me understand what's going on here and how I can correct it?

That does seem a bit odd, that things are still okay downstream of the problem that I latched onto. But even if the immediate problem is somewhere else, this one is still relevant, and could come up later.

 

[KenMitchell92]

Thank you for your in-depth explanation and solution suggestion. And for confirming my suspicion. The main issue I have had with this is getting the sound board setup with a feed to the camera. Our people operating the sound board are not that well versed with its operation so I'm going to have to find someone who knows how to implement the settings you have provided. i appreciated you taking time to respond and share your experience.