Magic Lantern Feature: AGC and why you need to disable it NOW on your DSLR

on August 26, 2014

The first feature you should make use of when you install magic lantern is Disable Automatic gain Control

Automatic Gain Control is something Canon installed on their cameras to make your sound quality more consistent.
In reality, nothing could be further from the truth.

What actually happens is that the first second or so of audio might be either higher or lower in volume while the camera figures out how to process and stabilize the sound.

The theory is great, but the inconsistency for the few few moments can make your audio unusable.
It’s amazing to me that this is a feature that is included by default when the actual microphones on DSLRs are terrible.
It’s not uncommon for DSLRs to have stereo microphones right on top also. Why you would want to channels of bad audio instead of just one is beyond me.

(Don’t get me wrong. The on-board mic is great for syncing sound, and we have returned to a time in digital filmmaking that more closely resembles the roots of cinema with clapboards required to sync audio. This is your best bet for good audio. It’s what’s known as “dual system sound” because you have a dedicated sound recorder with a boom mic attached and a sound guy running a mixer for you. The rode NTG-2 is a solid performer, and a lot of indie productions use this as their boom. Just a really great sound stage. You’ll get great audio, but it makes your “one-man” run n gun much more complicated.)

If you don’t want to sync in post, your next bet is to run a mic into a pre-amp, and then into the camera.

There are two good options: Juicedlink has a dedicated pre amp that is very popular.
JuicedLink 4-Channel DSLR Camera Microphone Preamplifier

Or you can take a mic, connect it to a Zoom h4n, and then plug that into your camera. The advantage if that is that you get an extra copy of your audio on the Zoom recorder.
Zoom H4N Handy Portable Digital Recorder

But the absolute cheapest way to get usable audio is to plug an external mic into your camera.
You can pick up a shengu-108 for next to nothing.

It’s dirt cheap, and leaves a lot to be desired, but it’s still a step up from the in board mic.
The Rode Video Mic PRO is a damn decent piece of hardware, is very self-contained and can just slide on top of your camera hot shoe.

Ok. Now you’ve disabled AGC but it sounds too loud or too soft.
Here’s a rundown of two other features:

Don’t just trust your headphones- look to see what you’re actually recording.
1)Make sure you have your AUDIO METERS.
The meters turn yellow at -12db, and red at -3db. If you gotten into the red, it means you’re clipping- that’s a bad thing.
This may seem obvious, but you want to stay in the green. Between -24 to -12 is a good range to start.

2)If you aren’t in that range, you can adjust your input volume using ANALOG GAIN if you are going straight into the camera from the mic. If you are using a pre-amp, you want to adjust your volume up on the PREAMP, and in Magic Lantern, turn it down low. This will give you cleaner sound amplified by the dedicated audio device and not the stills camera that you use for video that also just happens to have sound.

There it is!
Turn off AGC
Turn on meters
Adjust gain as necessary.

Better- use an external mic-single system
Even better- mic and pre amp- single system
Just the bestest- shotgun mic into external recorder synced in post- dual system.