A firmware hack for Canon 5D Mark II Audio Gain Control

by planetmitchLeave a Comment

Our friends over at cinema5d have a thread announcing a successful hack for controlling the Audio Gain Control (AGC) chip!

Have a tip, a video, or a Canon 5D2 product to announce? Give us a shout

“————— Success! —————

As an early goal, I have disabled the AGC for on the AK4646 audio chip that the 5D uses by overriding the sound_dev_task() at 0xFF856E60 to call audio_set_alc_off() at 0xFF856B14. The level is much too hot due to the wrong levels selected (it defaults to max gain?) but there is no shift in quiet scenes anymore. This is an easy first step that provides a proof-of-concept modification for the 1.0.7 firmware.

I can also log the audio levels as they are being sampled, which will make it possible to do on-screen level meters at some point in the future. My next step is figuring out how to add menus for the AGC disabling, then tackling the MVR_start_record() and LVAE_* functions.

<rant=on>
Canon, we are tired of waiting for you to act. So, without you, we will first fix the obvious problems, then we'll make it better. We'll probably help you sell more cameras, too.
</rant>”

Give the whole tread a read!

(Photo credit: snap from the thread on cinema5d.com)

Leave a Comment