using the front mic I can record to 2 audio chanels and control the gain of each channel discreetly. But when I plug an XLR in the rear and set audio ch1=ch1+ch2 I cannot control the gain for each channel separately. Is that correct or am I missing something?

That is correct (a frequently asked question; covered here many times before).

If you need separate levels then use a Y-cable to split the incoming signal.

If you're using a rear xlr,set the audio to "Ch 1". It sounds backwards, but that setting keeps the tracks seperate. typicaly I send my shotgun to the left and wirele lav to the right.
Bruce S. yarock
www.yarock.com

I do find this switch very dangerous for people who don't know the camera.

thanks Chris - I searched without finding a definitive answer.

strange that Canon should have dropped the ball with regard to the XLR in and got it right with the onboard mic.

rather than using a splitter another alternative might be to use the onboard mic 1/8" input. I think it should work well with many wirelesss receivers and onboard mics.

strange that Canon should have dropped the ball with regard to the XLR in and got it right with the onboard mic.Well, the onboard mic is stereo, so of course it has separate left and right volume control pots. And actually you've got the exact same thing with the XLR inputs too. If you connect an XLR stereo mic (not a common item, but they do exist), then you still have separate left and right volume control. There's an input level control pot for each channel.

What you don't have though is a separate pot if you're duplicating a mono mic input from channel 1 over to channel 2. And yes that is an oversight considering that a number of camcorders from other manufacturers have this feature.

rather than using a splitter another alternative might be to use the onboard mic 1/8" input. I think it should work well with many wirelesss receivers and onboard mics.I disagree. I think an XLR splitter would provide a much more robust and durable connection than the 1/8" stereo mini input. However as you point out it is definitely an alternative.

I agree the XLR connectors are more robust. I would certainly not recommend using the mini-plug with long cable runs.

The 1/8" input allows separate control of the audio channels even with a mono mic. I suspect that a stereo (two ring) connect cable is required. Fortuitously the sennheiser g2 wireless receivers I use ship with both an 1/8" to XLR and a stereo 1/8" cable