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Unique Solutions for Video Production

AGC Disable Section

AGC Disable - Improving Signal-to-Noise with Cameras without Manual Control

  • Is it time for you to get a camera with manual control?  In my honest opinion, yes ...
    • AGC Disable is a technique for forcing a camera that does not have manual control to throttle back it's noisy amplifiers.  This is done by injecting a high level signal into one of the recording tracks, and the camera senses that there is something very loud present, and it's Automatic Gain Control algorithm turns down its gain.  It became a necessity when the first DSLR cameras were released (5DMKII, 7D) which didn't have manual control when they were first released (they do now, with firmware upgrades from Canon).
    • AGC Disable is effective at improving the SNR of these cameras.  But, AGC Disable is not as effective as a camera which has manual control to begin with in terms of signal-to-noise performance.  You'll get better signal-to-noise performance with a camera with manual control
    • It's also a pain to deal with for a number of reasons.  You will sacrifice one of your recording tracks to use it.  The Riggy-Assist will force you to pan all of your mics to the left channel to use AGC Disable.  
      • Be wary of other approaches (either manually, or from other manufacturers offering AGC Disable) to record on the track where the AGC Disable signal has been injected.  Remember, your camera does not have headphones, so you can not monitor what the camera is actually recording.  You are injecting a signal at a very high level into the camera, and the camera can be freaking out (harmonics being folded back in-band, or 'clicks' and 'pops') and you will never know that your audio is being corrupted since you are not headphone monitoring in the camera.  
      • Attempting to record on the AGC Disable track is very dangerous, you could be recording corrupted audio and you will never know until it is too late, and that is why we don't give you the option to record on the track with the AGC Disable signal.
    • My recommendation is to get camera to one with manual control if you are at all serious about doing video production.  Even if you are not that serious, why would you want to deal with the hassle, and use something that doesn't yield as good of signal-to-noise performance.  AGC Disable was a necessity years ago when there was no other option.  Today, there are so many excellent cameras with manual control that are available at a very reasonable price (60D, T3i, T4i, etc).  A camera without manual control is no longer an appropriate tool in video production.  Honestly, it's time for you to sell your camera to a still photographer, and get a camera with manual control.  
    • If you are doing mission critical work, however, you may want to consider a camera that also has headphone monitoring (which will be more expensive).  But, you will have the confidence of knowing that you are monitoring what is actually being recorded in the camera (instead of what is merely present in the Riggy-Assist preamp).  It is still fine to use a camera without headphones with the Riggy-Assist, but you will want to add a step in your production flow to make sure that you playback your recording to verify it is there (a bad cable, or neglecting to insert the cable all of the way into the camera, would result in recording no audio, and you would never know while you are monitoring with headphones in the preamp instead of the camera). For more info, see the Playback Monitoring section of the User Manual.  For these newer cameras that also have headphones, metering, and manual control, we designed the Riggy-Micro preamp which rips out the AGC Disable, metering, and headphones from the Riggy-Assist, to create a smaller/lighter/more power efficient preamp.
    • We offer AGC Disable as an option in the Riggy-Assist because we understand that there are sometimes situations where you have to work with the equipment you've got.  I just need to make sure your expectations are set correctly that it is a compromised position, and it's my recommendation to upgrade to a camera with manual control when you can.
  • To Calibrate the Meter to the Camera
    • ​There is no factory preset, since every camera manufacturer is a little different in terms of what the maximim signal level is that they will accommodate.
    • If your camera has manual control (but no meters), then first throttle back the gain in the camera before following this procedure.  Note, if you later change the gain in the camera, then you will need to re-calibrate the meter.
    • Follow the calibration procedure on this video:
  • To Record Using AGC Disable:
    • Set the switches to the RED position, where AGC DIS is ON, and NORM/PanL is PanL.  This will inject a tone in the right track of the camera, and force it to throttle back its amps, and will pan all inputs to the left track.
    • Adjust your volume control for your mic so the 3rd amber LED lights up during the audio peaks, or the 4th red LED flickers occasionally.
  • Deleting the Right Track in Post:  Here are some tips on how this is accomplished using some of the popular editing software packages:
    • Sony Vegas
      • Right click on the audio track
      • Select "Channels"
      • Select "Left Only" for the final mix
    • Final Cut / Express - Method 1
      • Delete the right track
        • MODIFY > LINK, to unlink the audio from video
        • MODIFY > STEREO PAIR, to unlink the right and left audio tracks
        • Use the mouse to select the right track, and delete
      • Copy the left track to the right track position
        • Make sure teh "Auto Toggle" icon (the icon to the right of the "lock audio track" icon) for the right track is the only "Auto Toggle" icon activated
        • Use mouse to select the left track
        • COPY
        • PASTE. Since the right track is the only track with the "Auto Toggle" icon activated, it will paste into this track
        • You may need to select the right edge of the pasted audio track and expand (stretch) the track to fill the rest of the timeline
    • Final Cut / Express - Method 2
      • Delete the right track
        • Drag clip into timeline and select it with your mouse
        • MODIFY > LINK, to unlink the audio from the video
        • MODIFY > STEREO PAIR, to unlink the right and left audio tracks
        • Use mouse to select and delete the right track
      • Pan left track to center
        • Select (double click) the remaining left (A1 track)
        • PAN should currently read "-1"
        • Click the slider and move it towards the center so it reads "0"