I have a Lumix GH1 camera that has an external mic input. It takes a certain range of audio levels. I also own a Zoom H4 audio recorder that has a line-out output. Unfortunately, the output range of the H4 is wider than that of the GH1. When you connect them directly, the result is highly distorted sound on the GH1.
To fix this incompatibility, I decided to make a simple voltage divider circuit in-line with a mini-stereo cable. Since you need a cable anyway to connect the H4 to the GH1, this small circuitry does not add much to the setup. This DIY attenuator is documented in the following video.
The Zoom H4 is an audio recording device. You can take the WAV files it produces and sync them out with the video from the video camera in post production. However, for quick edits, the cable with the built-in attenuator proved to be quite useful. It reduces one extra step in post. The following video shows the setup in action in a field interview situation.
In summary, the DIY attenuator is simple to build with Radio Shack resistors that I happen to have in my electronics parts bin. While I needed it for my Lumix GH1 and Zoom H4 setup, it can be easily adapted for other applications.