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Canon EOS Crop Sensor for HD
APS-C sensor cameras including the 80D, 70D, 7D Mk. II, 7D, EOS M and Rebel models for HD video recording.


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Old March 22nd, 2010, 04:43 PM   #1
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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.
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Old March 23rd, 2010, 01:58 PM   #2
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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!!!!!!!!!!
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Old March 23rd, 2010, 02:57 PM   #3
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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.
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