Camera audio doesn’t have to sound bad…
It seems simple enough… Just start up your video camera, point it in the right direction and record your worship service. But while your visuals may be good enough, somehow the audio often suffers from excessive noise and distortion. The reasons are usually due to poor microphone quality and placement. A cheap built-in microphone on a consumer camera placed in the back of the room almost guarantees audio failure. What to do?
Well, plugging the audio output of your mixing board into the camera’s external mic input seems like a good idea — until you see the little 1/8-inch jack on the camera and realize it’s not a simple plug and play. Even if you do manage to kludge together a series of XLR to ¼-inch phone to stereo 1/8-inch mini TRS plugs, it’s still not going to work well. The causes are three-fold: incorrect signal level matching, power-supply noise and ground-loop hum.
The signal level problem occurs because the output of an auxiliary jack on your mixing board wants to make between -10 and +4 dBu signal level. That’s around 1 volt RMS, which is simply way too much voltage for your camera microphone input, which probably wants around -40 dBu (approximately 10 millivolts). You need to reduce the signal level coming out of your mixer by a factor of 100 while maintaining fidelity.
The power-supply noise problem occurs because the camera’s power supply is typically a very small and efficient high-frequency switcher design running at 20 to 40 kHz or higher. These supplies are notorious for injecting ultrasonic noise back into the camera’s audio signal ground. It sounds sort of like a million strips of bacon frying.
Ground loop hum typically occurs when two pieces of audio gear are plugged into different wall outlets. Standard AC outlet grounds in the same building can have up to 2 or 3 volts difference even when on the same phase. The resultant current flow causes a 60 Hz hum (around B flat on a Bass Guitar) which can remain constant and annoying even when the faders are pulled down on the mixing console.
The only way to prevent these noises from getting back into your entire PA system is to provide an audio isolation transformer between the output of your mixing board and the input jack of your camera. Your kludge cable wont work effectively because it sends too high of a signal level to your camera while providing no way to isolate the ground of your camera’s power supply from the rest of your sound system. But there’s a way to provide both needed items without breaking a sweat: use a camera audio DI box.
Now, you could build your own camera DI box out of a couple of guitar DI boxes and some kludge cables, but you can buy a complete solution for most any consumer or semi-pro camera. The company BeachTek, Inc. makes a variety of these cool boxes starting for under $200, and they include a camera mount so they can be installed between your existing tripod and camera. You then plug in an XLR cable from your mixing console, plug the 1/8-inch mini TRS plug into your camera’s external mic input and adjust the calibrated level controls for proper signal to your camera. It’s as easy as that.
BeachTek also makes models with built-in level meters, headphone monitoring and limiters. In addition, available models include 48-volt phantom power so you can add a professional shotgun microphone to your consumer camera. You can even split the audio coming into your camera using an XLR feed from your mixing board to send the full mix to one channel of your stereo track and local shotgun audio from the camera position into the other channel. That way, your video editor has the choice of how much camera audio from say, laughing children, to mix into the sound of the band on the other track. It will be perfectly synchronized and level matched, so you can video tape with confidence that your camera audio will sound as good as it originally did in the room. And that’s the name of the game.
For more information on camera audio DI boxes, please visit www.beachtek.com.