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This weekly course covers the most common questions videographers encounter when shooting and editing with DSLR cameras, from choosing a frame size and frame rate to understanding moiré. Authors Rich Harrington and Robbie Carman will also help you understand the impacts of compression and the difference between cropped (or micro 4/3rds) and full-sized sensors in cameras, and much more. This continual FAQ guide is a handy way to find the answers to the questions that plague you the most.
Richard Harrington: So one option in a lot of these cameras is that the microphone wants to run on auto, and in some cases it's not even an option. It's the only choice. Robbie Carman: Right, this is known generally as AGC or Automatic Gain Control. And the best way to think about Automatic Gain Control is that is the camera sort of being an automatic turner upper or turner downer-- Richard Harrington: Right. Robbie Carman: --depending on the volume level that is perceiving through its microphone. So something like me who's rather loud is talking close to the camera--the audio--the levels are going to get sort of turned down so I'm not going to peek out and be too loud and over modulate the signal.
Conversely, if you have somebody that's relatively quite, it's going to try to raise that level up to be you know sort for audible in--you know at a certain level. Richard Harrington: And in theory this sounds like a good thing-- Robbie Carman: Yeah. Richard Harrington: But it's really not. Robbie Carman: No. Richard Harrington: Because what's going to happen is something that's farther away from the camera is not going to sound like it is father away from the camera. It doesn't matter if you're right up on the camera making noise or you're farther away. Normally the camera is functioning as the eyes of the viewer. A lot of times serving as a point of view. So something that's farther away from the camera is generally expected to sound like it's off-mic or further away.
It doesn't want to sound like it is right there in your ear. Plus when it changes up and down, you know a microphone that's right here, you know, so if we have a shotgun mic right here and the person is standing right there in front, they should sound better than the person who's further away. Robbie Carman: Or louder rather, yeah. Richard Harrington: Yeah at least louder, but clearer, but as you crank that volume it's not a perfectly clean crank, right? Robbie Carman: No, and that's one of the problems of the AGC is that it can lead to when you have you know sort of separate levels that are you know some are loud, some are quite, it can lead to a phenomenon known as breathing where we can actually hear the AGC kicking in and then turning off, and then kicking in and then turning off, and it can be kind of annoying.
So, some cameras, my 7D not being one of them-- Richard Harrington: Yes. Robbie Carman: --let's just actually turn AGC on and off, which is a nice thing to have. I think your Nikon actually has the ability to turn AGC off. Let's go and take a look at that menu. Richard Harrington: Yeah, if I go over to the Microphone setting, it's going to give me five choices. Robbie Carman: Yeah. Richard Harrington: Microphone off; I would never turn the mic off unless we were doing something like maybe we're on a location scout and we were just getting B-roll. And you know, a lot of times it's amazing how people forget that the mic is rolling.
Robbie Carman: Yeah. Richard Harrington: So the only time I'd turn the mic off is if I was having a conversation that I didn't want recorded. Robbie Carman: Understood, understood. Richard Harrington: Other than that, you know if I was shooting in a loud environment, I might go for low sensitivity. My standard is medium or high, but there is that auto sensitivity that people will have and that's what's usually on by default. Robbie Carman: Right. Richard Harrington: So Nikon is giving us a choice; Canon is sometimes giving us a choice. It depends on models, typically we're seeing the newer the cameras that come out, the more likely they are to support this feature of turning off Auto Gain Control.
Robbie Carman: Yeah and other manufacturers have sort of come up with various schemes to sort of override Automatic Gain Control. For example, juicedLink which is a company that makes microphone preamps, the way that they're able to do it is they send out a very high frequency tone over the stereo cable that attaches to the camera. Richard Harrington: Something a dog could hear but not a person. Robbie Carman: Right, and that tricks the camera and goes oh, let me turn off AGC. So you know one of the things about AGC I think that's really important also to keep in mind, is that if you can't disable it on your camera, it's more--it's important then to sort of try to put something in front of the camera, say a mixer or something like that, where you can--or a preamp, where you can have greater control over level coming into the camera.
Because, again the way that AGC works is if it's noticing these varying levels, it's trying to act aggressively. But if it's getting everything at a nice, normal, solid level, which you can control if you put a mixer or preamp in front of the camera, it's going to not act as aggressively. Richard Harrington: Well not just a mixer or preamp, but often times a person. Robbie Carman: Oh, absolutely. Richard Harrington: In a professional video set it's not uncommon to have a dedicated audio engineer who's going to be paying attention to audio while the director of photography or the videographer is paying attention to video. It's pretty difficult to do both. If you are tasked with getting good audio and good video, then I think one of these smaller devices, like the Zoom H4n with its built-in meter, so you can have microphones running to your subject and, you know, mount this right next to the camera attached to the tripod, so while you're rolling you can glance down and keep an eye on the levels to make sure they're working. That's going to be important.
So it really it comes down to this. If you can't turn the Automatic Gain Control off, you have to outsmart it. Robbie Carman: Yeah. Richard Harrington: And that means taking advantage of either dedicated hardware or mixing better audio before it ever gets to the camera. Robbie Carman: That's right. Richard Harrington: All right.
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