AGC Vs Limiter

[Chris Santucci]

I always assumed that an audio limiter setting on a camera did the same thing as AGC. Is this not the case? I just watched a tutorial on YT where a videographer set audio levels manually and then turned the limiter on. Are these functions (AGC & Limiter) not doing essentially the same thing - preventing clipping?

 

[Alex H.]

A limiter does just that: keeps the audio from moving above the set dB value. That’s all it does.

AGC is Automatic Gain Control, and its job is to raise the overall input gain while also keeping the signal from clipping. AGC wants to make the signal as loud as it can get it. It disables the manual level controls because it is adjusting input levels on its own. (A limiter does not control the input signal.) This also has an adverse effect on the sound in most cases, increasing noise floor (not just self-noise from the mic and the camera’s pre-amps, but also the ambient noise floor) and often making the sound a bit crunchy.

So, yes, manually setting the levels and then adding a limiter to catch the peaks is standard audio workflow.

 

[Chris Santucci]

Thank you. Have you noticed pros using AGC for camera audio recording? I was shocked when I worked on a commercial job 5 or 6 years ago and the producer/director had his C200's set to AGC for an interview in a studio. I also have to wonder if camera preamps got better in the recent past, which were always poopooed by sound mixers I have worked with.

 

[Peter C.]

AGC used for unmanned cameras or run and gun where you don’t have time to manual adjust levels. In the situation you said if you’re a solo operator it’s difficult to impossible to conduct an interview maintaining eye contact and monitor both video and audio. Like anything can be misused by a lazy operator.

The downside of AGC is pumping in certain situations. For example ACG can misinterpret interview pauses and pump up the gain during these lulls. The result would be difficult to fix. Some devices like DJI mic mini implement it well.

Limiters on the other hand work completely different. When a level is reached commonly -6db will begin reducing the levels. Limiters are meant to catch occasional spikes so they don’t clip, but not meant as a set it and forget it. If gain is set too high it will sound bad.

Like ACG the implementation is equally important, many devices use digital limiters that will clip. They also don’t display when the limiters are engaging, so you can look at your level meters and see it’s safety below 0db with no red light light indicating clipping all the while there is too much gain and your audio is getting destroyed.

Quality analog limiters are very helpful for recording dialogue because you can get a stronger signal without fear of clipping.

Some prefer to record at a lower level for safety and in post add the audio sweeting they want. In other situations it’s better to use limiters or AGC while recording so audio is good enough. Example for this is live streaming and broadcasting where levels need to correct while recording.

 

[Alex H.]

Thank you. Have you noticed pros using AGC for camera audio recording? I was shocked when I worked on a commercial job 5 or 6 years ago and the producer/director had his C200's set to AGC for an interview in a studio.

Well, when I’m on set, that means there’s a professional sound mixer handling all things sound, so… not on my watch.

That said, I do often show up on location for Day 1 of a show and have to calibrate the camera for my wireless hop. There’s often an on-camera mic in the other channel. I know these guys go out without a sound mixer on other shows, and will typically set the cam mic channel on AGC. I turn that off and manually set everything.

It’s kind of an old-school news- and doc-shooter mentality, where the camera mic is there as a last-ditch failsafe. The idea is that it’s better to get it dirty than not to get it at all.

Using AGC for a studio interview is a pretty ridiculous decision.

I also have to wonder if camera preamps got better in the recent past, which were always poopooed by sound mixers I have worked with.

Camera pre-amps have improved greatly over the last 15 years. Honestly, they started improving when DigiBeta and other digital camera formats started gaining popularity in broadcast production. I think back to the days when I ran with a Shure FP33 in my bag. An industry-standard ENG mixer at the time, it didn’t hold up so well in the move from BetaSP to DigiBeta. The FP-series mixers were great with BetaSP and even U-Matic because the mixer’s pre-amps had a nose floor below the noise floor of the tape. Once DigiBeta rolled around, the noise floor was much less dramatic in-camera and the mixer’s weakness started to show through. That was around the time that Sound Devices hit the scene and pretty much rendered the FP33 obsolete.

There’s still no match for a skilled sound mixer with the right gear vs. a camp op handling audio directly in-camera, but the pre-amps are much less an issue these days than they once were.

 

[Doug Jensen]

Thank you. Have you noticed pros using AGC for camera audio recording? I was shocked when I worked on a commercial job 5 or 6 years ago and the producer/director had his C200's set to AGC for an interview in a studio.

I use Sony cameras with Sony wireless microphones/receivers and completely trust those combinations to handle the audio recording on AGC as well as any human could do it. Maybe better than human. I use the slot-in system on the Z750 and the MI-shoe on my other cameras. That gives the camera and receiver bi-directional communication, which makes all the difference. Now that auto-focus on the latest cameras is now nearly perfect, then getting audio levels to record properly ought to be child's play. And it is.

AGC won't replace the skills of a good audio tech in all regards, but for setting levels, yes.

 

[Chris Santucci]

This is really helpful guys, thanks!