The Gain Game: Bypassing AGC with an iPod at DVinfo.net

Ben Winter · March 22nd, 2010, 03:43 PM

The popular method of AGC bypass seems to be feeding a tone into one channel and audio into the other. Unfortunately there's no easy way to do that other than the juicedlink adapter, which is another $140 investment on top of an existing field mixer. The one thing holding me back was the investment into hardware that could be irrelevant at any moment.

I bought an old iPod shuffle for $30 and loaded a 20-minute mp3 of white noise at -6dB onto it, then plugged it into the R auxiliary input (headphone input jack) of my DXA-6. Conveniently, all beachtek adapters seem to have this form of input. The AGC is now gone and the remaining audio is clear as a bell.

I was skeptical about this whole jerry-rigging process of feeding noise into a channel, but I'm impressed. Plus, a $30 investment isn't one I'm going to regret when Canon/MagicLantern releases an AGC-disabling firmware update. If you have an existing field mixer of some type, I'd highly suggest the iPod over another $140+ investment.

White noise is preferable over a single tone because it provides constant power output over the entire spectrum, rather than a single frequency. It can also be easily generated via avalanche breakdown of a zener diode taken through some low-noise amplifiers, parts that can be had for under $10, and powered for hundreds of hours with a few AAs.

Mike Calla · March 23rd, 2010, 12:58 PM

hehe, when i first got my 7d i did the same with my little Sony mp3 which, get this, gets 70 per triple-A battery. works like a charm:)

BTW just viewed "The casket of lady Rowena" on your site. Absolutely great!!!!!!!!!!

Bryan McCullough · March 23rd, 2010, 01:57 PM

Good solution, but without levels or even being able to monitor what the camera is recording it's still not something I could put trust in for anything critical.

March 22nd, 2010, 03:43 PM	#1
Ben Winter Trustee Join Date: Jun 2005 Location: Hollywood, CA Posts: 1,675 Images: 1	The Gain Game: Bypassing AGC with an iPod The popular method of AGC bypass seems to be feeding a tone into one channel and audio into the other. Unfortunately there's no easy way to do that other than the juicedlink adapter, which is another $140 investment on top of an existing field mixer. The one thing holding me back was the investment into hardware that could be irrelevant at any moment. I bought an old iPod shuffle for $30 and loaded a 20-minute mp3 of white noise at -6dB onto it, then plugged it into the R auxiliary input (headphone input jack) of my DXA-6. Conveniently, all beachtek adapters seem to have this form of input. The AGC is now gone and the remaining audio is clear as a bell. I was skeptical about this whole jerry-rigging process of feeding noise into a channel, but I'm impressed. Plus, a $30 investment isn't one I'm going to regret when Canon/MagicLantern releases an AGC-disabling firmware update. If you have an existing field mixer of some type, I'd highly suggest the iPod over another $140+ investment. White noise is preferable over a single tone because it provides constant power output over the entire spectrum, rather than a single frequency. It can also be easily generated via avalanche breakdown of a zener diode taken through some low-noise amplifiers, parts that can be had for under $10, and powered for hundreds of hours with a few AAs. __________________ BenWinter.com

March 23rd, 2010, 12:58 PM	#2
Mike Calla Major Player Join Date: Sep 2003 Location: Shanghai Posts: 344	hehe, when i first got my 7d i did the same with my little Sony mp3 which, get this, gets 70 per triple-A battery. works like a charm:) BTW just viewed "The casket of lady Rowena" on your site. Absolutely great!!!!!!!!!! __________________ boxoutsidemedia.com

March 23rd, 2010, 01:57 PM	#3
Bryan McCullough Major Player Join Date: Oct 2003 Location: Richardson, TX Posts: 842	Good solution, but without levels or even being able to monitor what the camera is recording it's still not something I could put trust in for anything critical.