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NOT hearing Automatic Gain Control problem with Canon T2i
I have always read and accepted for gospel that filming interviews with the Canon T2i in video with the mic directly connected to the camera was not recommended because the AGC would raise the noise level volume when no one was talking.
I decided to do a little test today where I connected the a wireless lav mic to the T2i’s mic input and recorded a nonsense interview with myself where I talked a little, then went quiet for 3-5 seconds and then began talking again at the same volume level. I repeated this cycle twice.
My living room was fairly quiet however you could hear street noise outside (cars driving by)
Not only didn’t I hear the noise level raise during the quiet periods but when I began talking again the volume didn’t spike or sound any different. The street noise in the background didn’t raise significantly at all during the times when I wasn’t talking.
Did I somehow misunderstand the AGC issue?
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10 Replies
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They this in a busy room. If you start talking the room noise will fall off because the lav is going its good. Stop talking and the room noise will come up. Do a test with a TV or stereo going on in the background. If you have a controlled room the issue is not going to be that bad.
I do think a lot of the “Issues” are just things you need to be aware of and know when you need a work around. If you have a good mic and mic it close to the talent you can get better audio. But with something like the Zoom H4n you can get audio that you KNOW what you got. For me not being able to monitor the audio is the biggest issue with DSLRs right now.
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Hi Steve, I just watched (listened) to your test audio on Vimeo and I have to say…. The audio is terrible and I CAN hear the “breathing” of the noise floor raising when you stop talking and lowering when you start talking. It is quite plain to my ears. But I come from an audio background originally and I am listening in a professional audio monitoring environment, so your mileage may vary… To me this audio is completely unusable and a great argument why NOT to use the on camera audio of these cams.
Thanks for posting!
Richard Cooper
FrostLine Productions, LLC
Anchorage, Alaska
http://www.frostlineproductions.com -
Steve, I can hear the AGC kick in immediately after each last syllable. There is also general background rush/hiss during the quiet segments, in addition to the outside enviro noise. Bring your file from the t2i into your NLE and zoom in of the wave form. You may be able to see the results of the AGC.
John D. Frey
25 Year owner/operator of two California-based production studios.Digital West Video Productions of San Luis Obispo and Inland Images of Lake Elsinore
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I actually did import the videofile into my NLE to check out the waveform and I DO indeed see that it is not flat during the periods I am not talking.
Hmmm, maybe I do have to re-evaluate my earlier feeling of not hearing anything but it’s not as bad as I thought it was going to be…I was expecting much worse. I do hear it more when I listen on my laptop speakers as opposed to listening with my headphones, not sure why, could be my ears…I will have to check the owners manual, ha ha!
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Hey Richard, thanks for taking a listen!
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Thanks again for posting, Steve. I have not yet done a test on my 7D but I assume that it will be the same… unless there is a way to bypass the AGC.
Richard Cooper
FrostLine Productions, LLC
Anchorage, Alaska
http://www.frostlineproductions.com -
Yes, I would expect it to be exactly the same. There are a couple of hardware work-arounds.
JuicedLink makes a BeachTek type box that defeats the AGC while allowing you to monitor the audio as it is being recorded. It also has some simple audio volume controls
There’s also a “trick” that has you connect an ipod nano or shuffle to the mic input using a splitter which allows you to connect two mini-plug style audio input into the camera, you then record a tone signal on one channel only and play it back on the ipod into the camera. The camera “hears” the tone and it turns the AGC basically off.
But everyone else just records dual sound and then uses the Plural Eyes software to automatically sync your good audio to your camera audio. I sync manually for now.
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Does this audio problem with the T2i also apply to the 5D or 7D?
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Yep, the AGC issue applies to all the Canon HD DSLRs as far as I know. There is additional software you can download called Magic Lantern that fixes the issues for the 5D Mark II but no 7D or T2i version is available.
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