Thoughts on AGC limiting (pros and cons)

FarCountry

FarCountry

Member
The manual says very little on how the AGC works. Is it a sort of brick wall limiter? Does it completely prevent clipping? I will try to get some controlled tests going, but have not had the time to do it. Up until now, I have had it on, and have just tried to keep my gain settings as correct as possible to get as strong a signal recorded as possible without hitting into the red.

Anyone have a technical knowledge on this feature?
 
It isn't a "brick wall", it can't stop quick transient peaks from overloading and clipping.

But if there's a general overall loudness, it'll try to reign it in, starting at -6dB and attempting to keep everything limited at no higher than -4.5dB.
 
Thanks Barry. Is it generally considered bad form to use it? It seems to me to be good insurance for long form recording (like a wedding or recital) where something happens that is louder than anticipated, but I either can't react quick enough to adjust, or else my attention is temporarily on something other than the camera.
 
We always leave it on, unless we're doing scripted narrative production with a separate sound mixer that has its own limiter.

The second level of protection is to set your two audio channels to different levels, so that one is riding lower than the other; that way if the main channel "blows out" during some portion, the lower channel will stand a good chance of still being usable.
 
Thanks. That is exactly how I have been running. I had assumed that the AGC worked something like that, and had a case of some clipped audio on one of my cams and realized that I had no idea what the specs were on the AGC. Looking forward to your book BTW.
 
Far:

Also, in order to somewhat correctly set your levels, you need to adjust the levels with the ALC off, and then turn it on after they are set. Otherwise I have found you may actually be up against the ALC without knowing it, and setting the level higher than it should be.

I said somewhat correctly, because without a quantitative dB scale on the camera display, you are guessing anyway.

I agree that the on-camera ALC should probably be turned on in most cases. This is especially true with the XLR inputs as they usually have mics attached with a lot more dynamic range and with hotter outputs than the onboard mics and have to be reined in in live/event shooting situations.

Although the HMC-150 audio capabilities are good and similar to most other XLR input cameras on the market, you will get far better results with any off camera audio recording solution.
 
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