AGC Disable Y-Splitter Cable for Canon 7D & 550D / T2i Cameras

Emanuel

Emanuel

Cross-Examiner
«The DSLR-AGCY was developed to enable disabling of the Auto Gain Control in Canon and other HD DSLR cameras. This cable allows you to split your audio tracks. One end of the cable is used to stream a continuous tone from an iPod or other mp3 player to the camera. This fools the camera into lowering the audio gain. The other end of the cable is used to connect a microphone or preamp to the camera. Only one channel is recorded but that is easily resolved in post production by deleting the “tone” channel and duplicating your “good” channel. This provides a solution to the cameras’ lack of manual audio controls.

TRS 3.5mm Mini Male to 1 TRS 3.5mm Mini Male and 1 TRS 3.5mm Mini Female. 30 Centimeters / 1 Foot.»

http://cinescopophilia.com/?p=3087
 
Keep in mind that the whole "tone" or white noise to one channel thing doesn't disable AGC - it turns it on.

AGC is just an audio compressor/limiter - when sound exceeds the threshold of the limiting, it turns the pre amp input down, which is where the "pumping" sound comes from, especially concerning background noise, wind noise, etc. Louder dialogue, say, will push the gain down - gaps between audio will turn the limiting off, raising the volume of background, room noise, etc.

Feeding sound to one channel causes the limiter to stay kicked in, but it takes some testing to determine what the correct level of sound is to keep the limiter "squashing" the volume completely - so it's not bouncing in & out due to your mic'd channel passing the level of your noise/tone channel. You may find that this effectively kills much of the dynamic range of your audio as well.

The bigger issue with DSLR Audio is that it's pretty crappy - noisy preamps & limited dynamic range. I have't tested for crosstalk, but using too much tone in one channel could conceivably leak over into the other channel. Upgrading to a 60D is likely a much better alternative to trying to defeat AGC, but you still may not be pleased with the overall quality.

And finally, you can get male stereo 1/8 to dual male mono 1/8 at Radio Shack/etc, or on-line for $5 or so, and that's all this "miracle adapter" is - you don't need a purpose made cable for this. The bigger issue is with plastic molded cables, when the stereo jack is so fat it won't seat within the recessed connector panel of the camera.

I posted this on this thread:

Michael Carter said:
Guys, what do you expect from a camera purpose-built for stills with video as an afterthought (which is where DSLR video came from - "hey, we're sending a lot of pixels to the LCD, might as well capture that stream"...)

You're trying to get good audio from an unbalanced system that (to make things even worse) uses a 1/8" stereo mini jack, has no phantom power and has really sub-par preamps packed into a tiny space, a system where the quality of the audio capture was obviously a very very low priority?

I love my Canon DSLR, but my years-old DVX runs circles around it for audio capture, as will most any XLR-equipped box. People can get "acceptable" sound from it with adapters and runarounds, but how many gigs do you do where "acceptable" is what you really want to deliver? Especially for audio quality? Especially when a decent mic, a decent capture device and a little skill can give you crisp, pristine audio with presence and detail? Don't stick a great mic with a quality cable on a decent boom pole and run it through a clean preamp... and then into a 1/8 mini adapter and into Canon's lousy audio. Really, why, when there are solutions under $300 that will get 100% of the quality that your mics/cables/pres/mixers can deliver? Heck, get a $200 USB XLR interface and record right to your laptop. 2 channels of 48k/24 bit audio can be handled by some pretty old PCs or macs (and many cameras just record at 16 bits).

And keep in mind that noise reduction plugins are removing more than just noise - they can work wonders but they should really be for when you, your gear, or your plans screwed up - they shouldn't be thought of as a normal part of your production chain. They do kill some valuable content you may not miss in a 30-track pop song but you will in the line of dialogue that's the climax of your film. Really, I love DSLRs... but not their audio.
Click to expand...
 
Michael Carter said:
Keep in mind that the whole "tone" or white noise to one channel thing doesn't disable AGC - it turns it on.

gaps between audio will turn the limiting off, raising the volume of background, room noise, etc.


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This is a good point. I had to use my 550D to record a scratch track dialogue for a car interior instrument panel and it was in a very noisy parking garage. Even with the steady and loud background noise of everything from air conditioner units to motorcycles going by the limiter raised the background hiss to full volume between every copy line. I never heard any worse audio, ever. Better get an external recorder.

How is the audio control on the 5D, was it fixed by Canon, or a hack?
 
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I use an AGC Disabler cable with my Rode Video mic and found that I got better results when the input volume from my mp3 player (an iPod in my case) is at about 30% of its max volume. With much higher or much lower volumes the audio sounds like crap.
It's still just ref sound but can be used if my Zoom H4n ever has an issue - (forgot to switch on a Lav mic once :) )
Not done too much testing but it seems to be what works best so far. I hope this helps.
 
Michael,

You make some good points. But I need to correct a few points. The introduction of the "tone" does not turn on the AGC, AGC is always on. However, it does lower and stabilizes the in camera gain. If you raise the tone level too high, you may lower the gain so much that you can't hear your recording. It's best if you have a good strong signal coming form your mic and without monitoring capabilities you do need to test and calibrate your equipment.

I have tested and there is no crosstalk or bleed from one channel to another. The AGCY cable separates and isolates the right and left channels.

And you are mistaken about the cheap Radio Shack adapters. You do need a special purpose built cable for this application. The cable is not a "miracle adapter" but it is a specially designed and well built cable that separates the 2 audio channels; simple splitters duplicate the stereo ouput and will not work in this application.

Link to Sescom AGCY defeat cable. mp3 tone file also availble from product page:

http://bit.ly/i2MRIv
 
You can pick up splitters like this in the dollar stores and from online china shops, just make sure its a stereo to l/r mono splitter. There saved you 25$
 
markertek_dslr said:
Michael,

You make some good points. But I need to correct a few points. The introduction of the "tone" does not turn on the AGC, AGC is always on. However, it does lower and stabilizes the in camera gain. If you raise the tone level too high, you may lower the gain so much that you can't hear your recording. It's best if you have a good strong signal coming form your mic and without monitoring capabilities you do need to test and calibrate your equipment.

I have tested and there is no crosstalk or bleed from one channel to another. The AGCY cable separates and isolates the right and left channels.

And you are mistaken about the cheap Radio Shack adapters. You do need a special purpose built cable for this application. The cable is not a "miracle adapter" but it is a specially designed and well built cable that separates the 2 audio channels; simple splitters duplicate the stereo ouput and will not work in this application.

Link to Sescom AGCY defeat cable. mp3 tone file also availble from product page:

http://bit.ly/i2MRIv
Click to expand...

You are correct regarding AGC, though by saying "on", I'm referring to the application of gain reduction (or noticeable gain reduction). A compressor might always be turned "on", but won't begin compressing until a threshold is reached. (Refer to Bill Clinton's famous "that depends what is is"). (Or all the small-sensor "field of view" threads 'round here where we can write paragraphs about crop factor or simply say "your 50mm lens essentially becomes a 75".) Other than boutique gear designed to add color to a signal at all times, I sort of consider a compressor "on" when it's actually compressing something.

Also, please note that I specifically referred to stereo 1/8 to dual mono cabling; the stereo to two-stereo cable is not the same thing, it's intended for, say, using two sets of buds with an iPod. Stereo to dual-mono cables are indeed cheap (cost-wise), are indeed available at Radio Shack, and based on my testing with protools and FCP, add no additional crosstalk and do, indeed, separate the stereo input into two mono sources suitable for "tone or noise" tricks. Comparing the "purpose-made" cable to a headphone splitter and declaring it superior to such a cable may be correct, but it has no bearing on this subject (might as well mention that a coax SPDIF cable won't work for this either) and is misleading. In my testing, a $5 ebay stereo to dual mono works fine. Your item may use superior cable or jacks, but to say the cable I described won't work (and only yours will) is very misleading.
 
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