6D Audio Headphone Monitoring using Sescom Cable

[Neophyte]

In reading entries on or about October 14, 2013, it appears a developer released or compiled a source code at
https://bitbucket.org/OtherOnePercent/tragic-lantern-6d/downloads/magiclantern-Tragic.2014Jan03.6D113.zip to allow 6D audio headphone monitoring using the Sescom DSLR-550D-HOCF A/V Out Cable.  I've uploaded the latest magiclantern-Nightly.2015Aug18.6D116 build to my recently purchased 6D, and the audio headphone monitoring is not working with the Sescom cable.  What am I doing wrong?  Looking for guidance or a workaround to use the headphone monitoring with (or without) the Sescom cable on the 6D.

[simonm]

I'm interested in this as I own a 6D:

Have you tried to debug/diagnose this systematically?

1. Record a clip with correct audio levels.
2. Play the clip back and check to see if audio is output through the Sescom cable:
    2a: loud enough to drive your headphones? (I doubt this will work)
    2b: loud enough to be an input into some other audio device, such as an amplifier, mixer or aux. input to something like a car stereo?

If you get audio from either 2a or 2b, use whichever setting worked, to then...

3. try to monitor a recording in the way that worked with (2).

If you get nothing (which I would expect) the "problem" is either Canon's firmware or the ML extensions.

But it's not a real problem, it's most probably a design decision: I would expect audio in the AV output to mute during recording. Otherwise, unless you do something downstream of the camera, any video monitor connected (that has a speaker) will cause a howlround (or at best an annoying echo) once you start recording. Same with HDMI output (actually I think it says that happens with HDMI in the ref. manual).

In any case, I would be _very_ surprised if you can drive headphones nicely directly from the camera under any circumstances (but pleased as it would occasionally be useful!). Most of this sort of kit uses -10dBv as its "line" reference level, and the signal is thus too quiet to drive all but the lowest impedance and most sensitive headphones.

You _might_ get something audible from the earbud things used in mobile phones (they are typically pretty low impedance), but it will probably distort horribly, as the output amplifier in the camera isn't designed to deliver the necessary current for headphones.

If you do get it working, you are unlikely to permanently damage anything, but you may find you drain the 6D's batteries pretty fast. It's a much better idea to get either a small headphone amp you can feed from the camera, or (better) an audio location mixer you can use as a mic pre-amp and do your monitoring from that, treating the 6D as an audio 'black-box' input-only device whilst you are actually recording. There's quite a lot on the market now including mixer/recorders (audio to SD card, etc.) and they're really cheap, considering.

Hope that helps.

S.

[Neophyte]

It appears 1% (one of the ML build developers) last ML activity was on December 23, 2014, 12:12:32 AM.  It was unfortunate the latest 6D nightly build (August 2015) does not include 1% source code for the Sescom DSLR-550D-HOCF audio interface. 

I tried what simonm recommended and the results were the same--no audio using the Sescom cable.  I will await for other suggestions or an updated 6D build that will fix the Sescom cable interface problem.