There are many options available to backup your audio. Most of the time I operate believing that the audio captured in-camera will be problem free. Under these pretenses I roll a flash recorder with no timecode sync or clapping so the audio is available just in case everything else goes wrong.

If you did have to use backup audio, syncing is not as big of a problem as it used to be with software like Plural Eyes. This FCP plug in allows you to sync multiple sources without timecode, video and audio, as long as there is some sort of scratch track on each source. It compares the audio signals from the different sources and automatically syncs them.  This is a great tool for productions shooting on the 5D. With just the built in camera mic or preferably a reference audio track of some sort you can sync your audio recorded by your sound recordist without the extra steps of slating and clapping.

One of the biggest annoyances I have when doing sound with the extremely broad range of cameras available now is the lack of familiarity with how each camera processes audio. I’ve fed audio to just about every professional camera made (see credits) but with all the options and layers of menus it’s difficult to be 100% confident in the product being recorded. Confidence is paramount during film and video production and this is why the extra step of dual system audio can ensure your project gets completed without issue.  Even the most experienced sound engineer can’t guarantee problem free audio when sending audio from his $2,000 microphone to his $3,000 mixer through the $2.00 iPod cable.  With cameras progressively moving away from a standardized audio input section, dual system acquisition appears to be here to stay and you should get familiar with how you can make the workflow work best for you.

Sound Devices has a nice article with all the tech specs about sending audio to a Canon 5d MkII. You can see it here.

Another thing I would recommend when sending audio to a HDSLR is to listen to a test recording from the flash card after it’s been transferred to a computer when your setup is totally finished and you are ready to roll on your scene. In addition to the insecurity of using the $2.00 cable another thing that the Canon 5d MkII lacks is the ability to record balanced line-level signal. The reason to check a recorded sample just before your scene is to ensure that no electrical interference is passing from your lighting, ballasts and monitors into your mic-level audio cable.  Since there is no way to confidence monitor the audio being recorded the next best thing is to listen to a test after every light and cable is placed. Listening to a test from the built in speaker may not allow you to hear this type of interference if present.

Lastly, as is always good practice with audio, make sure that your audio cables are running as independently as possible from the mixer to the camera. NEVER travel audio cables parallel to power cables, avoid Ballasts like the plague and as much as possible keep your audio away from anything else with a current;)

Good luck!!!!

Lance