I’ve been getting a lot of questions about the audio cable I use between my Eos7D and my ZoomH4n or Sony PCM-D50 audio recorders. It’s not as some have suggested just a 3.5mm jack to jack cable, but instead features a -25db PAD, it is essentially a carefully made cable with a resistor that attenuates the output. This reduces the output volume of the audio recorder to a more friendly mic level input that the 5DmkII or 7D can cope with. I had it specially made by John McCombie at Pinknoise systems in the UK, he specialises in audio bits and bobs. You can contact him at firstname.lastname@example.org
Warning, it does NOT defeat the cameras in built AGC but it does give as good as the standard camera can give without using a hack like Magiclantern for 5DmkII from Tramm Hudson. You can of course record on the recorder as well and use the cable to provide a nice clean guide track for later syncing in your editing software. The amazing Pluraleyes software for Final Cut can of course be used to automate this.
Another thing, the Zoom H4n shares its line out with the headphone socket so there is no way to monitor with headphones when using this cable. Maybe someone can make a suitable y-splitter cable. The alternative is to use a recorder like the Sony PCM-D50 with its separate line out and headphones jacks, with this combo you can monitor too. Sadly the Sony does not have XLR sockets, seems you can’t have it all.