Auto Gain Control defeat - A77

David Kilpatrick
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Auto Gain Control defeat - A77

Unread postby David Kilpatrick » Tue Jul 31, 2012 12:02 am

I've been experimenting and will produce a full report and video soon.

Basically if you have an iPhone, iPad or iPod Touch you can get an App called Tone Generator Pro for 69 pence.

This app can generate a 20kHz sine wave tone. If you get the level right (not easy, I needed to use a preamp, or at least so far) you can feed this to one of the stereo sides, and it will lock down the auto gain perfectly. This is how the existing AGC defeat preamps all work, they all require you to be left with just a mono track.

I have more experimenting to do using a better studio mixer and stereo sound, and I need also to get the mic level higher after defeating the AGC. This may call for more precie control.

However, in principle you can spend 69p plus a connecting cable or two and get an AGC-defeat system for Sony cameras if you have an iOS device - and I am sure that an Android equivalent app will exist.

David

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pakodominguez
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Re: Auto Gain Control defeat - A77

Unread postby pakodominguez » Wed Aug 01, 2012 12:32 am

http://www.adorama.com/AUTSIM2.html (55 $)
http://www.adorama.com/AUTSIXZMIC.html
but actually, I do prefer (actually, I bough it, just need more time for playing with it) this
http://www.adorama.com/AUTSDR40.html
with a cable like this for monitoring the sound
http://www.adorama.com/SEMICMON.html
OK, this are not 99 cents solutions...
Pako
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David Kilpatrick
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Re: Auto Gain Control defeat - A77

Unread postby David Kilpatrick » Wed Aug 01, 2012 1:24 am

The monitoring cable might be of use in an iPhone rig. However, the rest are not. They are all require an app to be running on the iPad or iPhone - I have two such modules, an iRig and an Alesis iOdock. Basically, if you are running the tone generator app, you can't run a second app, since these devices do not multitask. So you can not either run a mic through the iPad, or use the adaptor as a preamp, while also generating the tone.

By all means take a look at the video I have produced as a pilot for the BJP -

http://youtu.be/d4v6XOLLe-A

This is a private video, please do not share the link beyond this forum post as BJP will either say, just post it in your own space, or take the video from me and incorporate it in their App.

I have not been able, despite trying any cables and even a small battery FX unit (Pandora 2) to get the iPhone 20kHz signal to work when injected alongside a normal mic. it totally kills all mic sound regardless of level. I don't know exactly why (it may something to do with the way the iPhone outputs audio, or the way I am connecting the two). I am sure there is a solution which could allow an iPhone to be input beside the mic, and control the gain.

Meanwhile, the only way I've been able to make it work is using a studio mixer. My method produces a full stereo recording not a one-channel mono, so it's a little better than spending money on BeachTek or Juicedlink boxes even though those do offer many other benefits (mainly for Canon owners).

David

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pakodominguez
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Re: Auto Gain Control defeat - A77

Unread postby pakodominguez » Wed Aug 01, 2012 5:50 am

David Kilpatrick wrote:The monitoring cable might be of use in an iPhone rig. However, the rest are not. They are all require an app to be running on the iPad or iPhone - I have two such modules, an iRig and an Alesis iOdock. Basically, if you are running the tone generator app, you can't run a second app, since these devices do not multitask. So you can not either run a mic through the iPad, or use the adaptor as a preamp, while also generating the tone.

why do you want to stick to this app? Or are you looking for an iPhone solution only? Tascam have a series of products for iOS users (http://tascam.com/products/iphone/) and what looks best for you is the iU2 Audio/Midi interface ) http://www.adorama.com/AUSTIU2.html)

I was looking for a while for a sound solution, For me iOS are not an alternative because my phone run on Windows phone (7.5, I love it and even if it is still limited, app-wise, I do prefer it to other OS) and my table runs on Android 4.1, where I can find more apps; but the best audio solution I found was the Tascam DR-40 that works as mic and recorder; have 4 channels (2 adjustable mics plus 2 x XLR/TRS Combo Inputs) and a 3.5mm Headphone-Line Out, so actually I can record AND transfer the audio to the camera with the Mic-Mon cable. As I said before, this is a 200 $, not a 99 cents solution, but make life easier.
David Kilpatrick wrote:By all means take a look at the video I have produced as a pilot for the BJP -

http://youtu.be/d4v6XOLLe-A

This is a private video, please do not share the link beyond this forum post as BJP will either say, just post it in your own space, or take the video from me and incorporate it in their App.
this is definitely a private video: no way to watch it...
Pako
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Re: Auto Gain Control defeat - A77

Unread postby David Kilpatrick » Wed Aug 01, 2012 1:40 pm

Pako, do any of the systems you mention have a function to generate a 20kHz signal at an adjusted level and feed it in with the mic? That's the whole point of this. None of the other solutions, Tascam etc, have any effect on the Auto Gain Control circuits of the A77. I already have a Zoom which can record and feed to the camera at the same time, but it won't defeat AGC and requires me to convert and paste in the Zoom's audio to the video, in sync. It will do 2+2 surround sound as well as stereo, but I have no great interest in spending hours on audio dubbing. I'm looking for a way to make the A77 match the EOS 600D, that's all.

It does not matter whether I use Tone Generator Pro, or an alternative; there are various sine wave generators of a similar type, it's just that this one is kept up to date and is well supported.

Considering that the alternatives suggested by video-audio sites include recording a 20kHZ tone on a spare mp3 player then adding that to the mix (first make your 90 minute long recording), the iPad/Phone/Pod or similar Android/other solution seems worthwhile.

This is not about how to connect mics to DSLRs, I've been doing that for a long time. It's about how to set up AGC defeat without buying a $400 BeachTek or Juicedlink mic preamp box.

I have changed the video from Private to Unlisted. That way anyone reading here can see it without my needing to enter YouTube details into the sharing list.

David

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pakodominguez
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Re: Auto Gain Control defeat - A77

Unread postby pakodominguez » Wed Aug 01, 2012 3:03 pm

Hi David,

David Kilpatrick wrote:Pako, do any of the systems you mention have a function to generate a 20kHz signal at an adjusted level and feed it in with the mic? That's the whole point of this. None of the other solutions, Tascam etc, have any effect on the Auto Gain Control circuits of the A77. I already have a Zoom which can record and feed to the camera at the same time, but it won't defeat AGC and requires me to convert and paste in the Zoom's audio to the video, in sync. It will do 2+2 surround sound as well as stereo, but I have no great interest in spending hours on audio dubbing. I'm looking for a way to make the A77 match the EOS 600D, that's all.

I understood I was getting into a subject I don't really master that well. I did understand that the Tascam/Zoom solution that many videographers are using on their DSRL was not what you were looking for. I suspected you already own one of these devises. The Tascam page for iOS is mostly solutions for record in the iPhone, not for Line Out -definitely not what you are looking for. BTW, on the video I can see only one connection to the iPad, coming from the console. How are you feeding the Audio to the A77?

My point was that the Line Out of the recorder feed the audio to the camera (no idea if at 20kHz, I have to check the manual...). What people are doing is controlling the gain with the recorder. The file they record (if they record anything on the devise) is just for backup -no need to use it unless you screw something (noise, a bad connection...) during the shooting.

I have so many things I want to try, and so little time. My cousin, who is a sound engineer, was supposed to come during the spring, and we agreed to trade a couch in NYC against a workshop on recording, but it didn't happen yet... In the meanwhile I'll try to record my niece, who's thinking about becoming a performer (she has a beautiful voice, and the guts...) and my friend's daughter, singer of a folk band in Argentina (http://www.loshermanosmckenzie.com.ar/) when she visit NYC in a couple of weeks.
Pako
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David Kilpatrick
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Re: Auto Gain Control defeat - A77

Unread postby David Kilpatrick » Wed Aug 01, 2012 4:06 pm

The recorder won't prevent the camera from applying auto gain though. I have had various results, some better than others, using preamps and recorders but none of them will really disable AGC.

The required and desired answer is for Sony to put firmware in the camera which can just switch off AGC and provide even one fixed level of input. It would be nice to have level meters and 32 steps of volume control etc like Canon, but even just a single fixed sensitivity pr a High, Medium, Low setting like Nikon would be great.

David


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