However, the only microphone that Canon sells to go with the camera is an expensive Bluetooth mono microphone kit, the WM-V1 Wireless Microphone. All other microphones I saw had to connect to a special input shoe, and that shoe doesn't work with my camera. Nobody else seems to sell any other mike or adapter for this camera, and I couldn't find any info on the pinout of the connector to make one myself.
Somebody has got to figure out how to make an adapter and attach a reasonably-priced microphone or two to this camera...
Step 1: The connector pinout
It's a 4-wire 3.5mm (1/8 in.) jack. It's set up for use with a typical consumer mike, and it can be used with a dynamic mike or an electret (condenser) mike. Electret mikes need external power to function, and can have either two or three connections. For a two-connector electret, the mike power and signal are carried on the same line, and for a 3-connector electret, the power and signal are separate. A cellphone external mike uses 2 connectors, while a PC mike uses 3 connectors.
The Canon jack supplies mike power on a separate line, so you can ignore the mike power lead and use a dynamic mike, or use a cheap PC mike powered by the camera. Great!
Step 2: Simple mono PC-microphone to camcorder adapter
This adapter has two problems, though. First, adding an additional mike (or two if you adapt it for stereo) may reduce camcorder battery life, and with a stock Vixia hf r300, we're talking a short battery even before adding additional power drains. Second, PC mikes are designed to work with about 5Vdc going through a 2.2k resistor, and the Canon's voltage output is under 3Vdc and I don't know what kind of resistor it's through (maybe none). Remember, this was designed to power their Bluetooth kit. Because of all this, the mike's sound levels will be low, much lower than the camcorder's built-in mikes. Not too bad of a problem with a good video/audio editing program, but it could be better.
Step 3: Better adapter for PC mike to camcorder
Once again, this thing's shielding has to be bulletproof. For the case, scrape paint away from the screw holes and the input jack so everything has good continuity to the camera's cable shield.
The setup above is what I'm using since I only need to record mono. I've made a schematic for a stereo adapter as well, but I haven't tested it. Should work, though.
Step 4: What about my professional XLR Lavalier studio rig?
That said, however, if you have professional mikes, chances are that you have pre-amps and possibly some mixing equipment and amplifiers and stuff. If so, your equipment can probably produce a consumer line-level output for recording on DVD or PC or whatever. If that's the case, you can use this circuit to convert the line-out signal from your setup to microphone input levels that are compatible with the camcorder.
As before, I haven't tested this, but it should work, and if you have the ability to pot the signal up or down, you're all set. The camcorder has a VU meter as part of the display (at least mine does), so adjusting your levels is a snap.
Shield everything, always. Cheers folks!