So I'm using a ProFX12 for video production (it was free, used one from my uncle who does radio). There's this odd buzzing sound in my audio though. My mic input to mixer is XLR. My mic output is 1/4" Y cable > 1/4" stereo cable > 1/4" to 3.5mm adapter > camera. Here's what I've tried:

1) Switched mics. No change

2) Unplugged all mics. No change.

3) Zeroed out all channels. Muted all channels. No change.

4) Unplugged everything from the mixer except the power and the main output. No change.

5) Unplugged the 3.5mm from the camera. Sound disappears (so its not the camera).

6) Plugged everything back in. Made sure the only thing on the circuit was the mixer. No change.

7) Tried plugging the mixer into other outlets. No change.

8) Detached output and plugged headphones into mixer instead. No change.

9) Tried using tape out intsead of main out. Can't get any audio so i guess tape out doesn't work.

10) Plugged everything into my desktop instead. Buzzing sound is more of a high pitched whine now, that could just be my onboard sound not being very good.

So I think its the mixer, but I can't figure out for the life of me what's wrong. I've seen lots of people with similar problems online but none that exactly match this. Everything points to a ground loop or some other ground problem, but I tried a GFI outlet too, and mad e sure the mixer was the only thing on the circuit. When my uncle got rid of this board, he did so because the #1 XLR input stopped working. He never mentioned anything about noise interference. If you want to know exactly what the sound sounds like I did produce one video you can really hear the sound after 1:55. Prior to that has other, unrelated audio struggles

Anyone know what I'm missing? Is my mixer just broken?

1 Answer 1


Firstly, you need to make sure the camera AGC (Auto Gain Control) for audio is OFF. You can hear the buzzing change in level in the background - it pumps up and down as the audio level changes.

This also indicates that he buzzing is generated in the mixer. If you don't have a balanced input to the camera, and you are using unbalanced connections to the camera, you have probably got a ground loop going on of some variety.

Can you please edit your post and explain what you are using for a camera?

I see a potential issue with the mixer connection to the camera. Is the camera running on a mains connection or is it battery powered?

  • So I'm using a Canon EOS Rebel T2i. There is currently no way to disable the AGC that I can find. However, I did find some sound samples of what that sounds like and its just white noise. If I could remove the buzz and just be left with white noise, that's much easier to deal with in post. Commented Jan 19, 2019 at 7:43
  • I'm running 1/4" through adapters from main output to camera, I'm pretty sure 1/4" is balanced. Found this cable a few minutes ago and tried it, its single channel XLR to 3.5mm with no adapters, just a straight cable. Tried that, no change there's still a buzzing. There's no way to adjust any sound settings on this camera either, the only option is to turn sound recording on or off. Commented Jan 19, 2019 at 7:56
  • OK T2I is basically unbalanced audio in at mic level. There is an AGC Setting in the menus. You have to unbalance the audio at the mixer. If your mixer is outputting a balanced connection, look for a "tape out" or other similar unbalanced connection. If not available, you will have to unbalance the connection yourself. signal is on pin 2 of the xlr. Ground is pin 1. Bridge pins 3 and 1 to unbalance the connection correctly . Do this for both left and right, then you should be able to wire up a connector to the T2I for audio.
    – Mark
    Commented Jan 19, 2019 at 10:50
  • So I just tried using tape out to camera, buzzing is still there. Also there is nothing in the settings to disable AGC on T2i and the only way to disable it i've seen online is to jerry-rig it with a bunch of adapters, which doesn't work for everyone, it seems Commented Jan 19, 2019 at 20:01
  • OK understood Maybe I am thinking of the 5dii. If there is no AGC then you cannot record sound on this camera. you will need to find an external device to record sound and simply use the audio on the t2i as a guide track. You will then need to synch the external recording with the guide track on the t2i.
    – Mark
    Commented Jan 20, 2019 at 3:05

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