A Few Audio Questions From a Newbie

[Michael Maloney]

Coming from a 40 year professional still photographer background and just getting my feet wet in video, I'm finding the audio learning curve very steep. I'm hoping someone can answer some very basic questions for me.

Here's my setup :

Canon 5D Mark II
Magic Lantern firmware (Thanks Tramm!)
JuicedLink CX 271 mixer
Rode NTG-1 mic connected to JuicedLink via xlr
Headphones with Boostaroo amplifier

In Magic Lantern, what is Output Volume and Analog Gain? What level should I set them to as a general starting point in relation to the left and right gain settings? Should I rely on the volume bars at the top of the screen? Or should I rely on what I hear in the headphones? Where should my pre amp gain switch be on the JuicedLink mixer. On high to start with? How about trim?

Again, I apologize for these very basic questions. I've played around with all the variables, but since I don't really know what I'm doing, I'm a bit lost. Any help will be appreciated.

[Chris Barcellos]

Hi Michael:

I will try to help

1. In Magic Lantern, what is Output Volume and Analog Gain?

Output volume is level going to monitoring jack out.
Analog gain raises the recording level actually being recorded.
Digital gain also does that, but through a digital raising of level. Jon Fairhurst recommends keep digital as low as possible.

2. What level should I set them to as a general starting point in relation to the left and right gain settings? Should I rely on the volume bars at the top of the screen?

Headphones should not be relied on. You need to listen still, but keep levels in green is the goal. Pushing to red orange or red will get into clipping of the signal.

3. Where should my pre amp gain switch be on the JuicedLink mixer.

I use the 231, not sure of the 271. I start out high. While the preamp in the 231 is, I wish it had a bit more oomph... Start out with Camera setting in Analog at about 10. At one point, Jon Fairhurst liked to keep digital gain as low as possible, but you may have to play with your set up to get where you are satisfied. Remember, the more gain you add, the more chance of noise showing up. However, I have worked with digital gain around 12 to 16, and have had decent success. Oh, make sure AGC is off in the the Magic Lantern mode, and that you have selected external microphone.

One reason you set at two different levels of gain is that the higher level track can be used for quieter dialogue, while the other can be used to pick up louder noises that may "blow out the other track".

[Jon Fairhurst]

In general, I run the JL at full gain, high. Analog gain in the camera +10dB. Digital gain +0dB. If I need more oomph, I increase the analog gain to +17dB. If I need less, say on a scene where the actor will scream, I turn the JL knob down. If the mic is consistently too hot, I'd turn the analog gain down to 0.

The reason I keep the digital gain at 0 is that anything else throws away bits. I'd rather record on the soft side and boost in post than throw away dynamic range.

[Michael Maloney]

Thanks Chris and Jon.

It's starting to make sense to me now. Still not sure what you mean by "digital" gain. In Magic Lantern I only see an analog setting, so how do I go about adjusting the digital gain?

(Btw, my Juiced Link is the CX 231…I mis-typed in my original post.)

[Jon Fairhurst]

I don't have it in my hand, but I think it's Mgain (analog) and Dgain (digital).

[Bill Binder]

I make a lot of music recordings using pro audio gear unrelated to the 5D2 (mostly jazz BTW), and my thought on digital gain with respect to the 5D2 kind of goes like this: why do it in-camera and risk clipping when I can do the exact same thing in post without that risk? It's pointless, so try keeping your digi gain to a minimum (preferably zero), then use your external analog gain from a pre-amp next if you have one (because it's likely way "cleaner" on the s/n front, and then lastly use the analog gain of the 5D2 -- with the goal of getting your signal as hot as possible (because that's where your resolution is) without risking clipping (because once clipped, there's no way to get back the waveform).

As a side note, most preamps have kind of a sweet spot where they run "best" (although best is hugely subjective). Often, that sweet spot is somewhere slightly backed off from max gain. So, knowing absolutly nothing about the JuicedLink (meaning take this with a grain of salt), and knowing that running zero analog gain can also be less than desireable for any given op-amp, there's probably a point where you might be better off backing off the JuicedLink a bit (from full max) and bumping the camera's analog gain one notch so as to run both op-amps closer to their own sweet spots. But again, it depends on the specific gear.

[Jon Fairhurst]

Bill, your philosophy on setting up gain is spot on.

Regarding the JL, it only puts out 18dB of gain max, so you can crank it full steam ahead without going past the sweet spot. I think this is the only piece of audio gear that I run at full tilt. Like Chris, I wish the JL allowed more gain than it does. It feels a bit like a Ferrari with a wooden block under the gas pedal. During the first week I owned it, it just felt wrong to go past 2/3 gain. These days, I'm upset if the gain pot isn't fully clockwise. ;)

[Chris Barcellos]

Originally Posted by Jon Fairhurst

I don't have it in my hand, but I think it's Mgain (analog) and Dgain (digital).

.....and when you get into editing the config file you generate by saving the ML setting to your card, you can actually set digital gain at two different levels.