Canon T2i/550D 7D Disable AGC Automatic Gain Control Hack for the Rode Videomic

– June 30, 2010

I finally figured out how to bypass or disable the AGC on Canon’s T2i 550D and 7D using the Rode VideoMic.

As you can see by the video below I finally figured out how to disable or bypass the AGC (Automatic Gain Control) on my Canon T2i 550D while using the Rode VideoMic. (This will work for the Canon 7D as well).

I ran across a good video by Mike B at IamTheMikeB.com, he explain how to disable the AGC  which I had to give a try.

But I couldn’t get his hack to work for my Rode Videomic and judging the comments on his video no one else could either.

I made 3 trips to Radio Shack but none of these adapters worked. Don’t buy the ones I got if you have a Rode VideoMic.

I didn’t want to get a JuicedLink or a Zoom H4N or anything else that would add time and steps to my DSLR video workflow, I like to keep it cheap and simple.

Part 1

Part 2

Part 3 – Where You Can Buy The Cable

Perhaps someday Canon will be nice and provide a firmware update for the AGC, but I didn’t want to wait any longer.

The problem is Canon designed a poor automatic gain control AGC which would have been better if they left it out of the design all together.

What happens is if you talk really loud into the microphone the AGC will bring your level down which eliminates the hiss, but only 1 second later after you stop talking it brings the level all the way up again (along with the hiss).

What we want to do is clamp the AGC down and keep it there to keep the hiss away so we can have nice clean audio.

To do this I used an old cheap mp3 player I had collecting dust to playback a 1 hour 19kHz sine wave tone by sending the tone into the right channel of my T2i, and the Rode mic in the other. I like using the mp3 player because I can control just the right amount of tone to the right channel so I get the full clamping effect but not too much to have the tone bleed over to the mic channel.

What Mike B figured out which was the AGC worked in tandem for both channels which meant you only need to clamp down one channel while you use the other for your mic.

Now what really screwed me up was the audio adapters from Radio Shack, I pinned them out with my multi-meter but I couldn’t understand why it was not working when other mics worked fine, so I then tried using my alligator clips to figure out how the Rode video mic was wired and that is when I found the answer.

The Rode Videomic connector was not wired like I thought, normally on most mikes you just need the tip and the ring, but with the Rode mic you need to carry the sleeve in your connections (something the Radio Shack adapter won’t do).

I created my own adapter with the tip and sleeve carried through and it worked perfectly!

So what I do when I bring the audio track in to Sony Vegas is to right click on the track and click on left track only and I am good to go since the Rode mic is mono anyway and only needs one channel.

In my next video I will show you how I wired it up. I should have that done soon.

Download the 19kHz tone (one hour long). (unless you are really young you will not be able to hear this).

Update 1:

One of my reader Salvic is making this cable for sale.