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Problem: BeachTek output levels OK, ML-equipped 5DM2 reduces the same signal

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    Problem: BeachTek output levels OK, ML-equipped 5DM2 reduces the same signal

    I've been Googling about without much luck due to old AGC discussions and the like; hence, I shall pose my specific quandary:

    I'm presently running a Canon 5D Mark II with Magic Lantern. I also have a BeachTek DXA-SLR which I use in conjunction with it, but have had some difficulty attaining good audio levels without running the BeachTek's with the preamp gain on the "HI" setting (15db gain), and the trim controls around ~7 or ~8. Goes for both my cheapo Audio Technica battery-powered lavalier mics, and my phantom-powered Rode NTG2.

    This is with Magic Lantern running a full 32db of analog gain (!), no digital gain, and AGC turned off (off in both ML and on the BeachTek).

    I decided to plug the BeachTek's 1/8" output (the one that generally connects to the camera's 1/8" mic input) into my computer, and monitor the audio levels with Audacity. In this capacity, the BeachTek put out more than respectable audio levels, even with the preamp gain set on "LO" (0db gain) With the preamp on "HI," I have more range than I know what to do with, and can easily go straight past -6db and peak way past 0db if I jacked up the trim controls even close to full. The green lamps on the BeachTek correlate this.

    Obviously, the BeachTek is working as intended and putting out a respectable audio level; hence, one would expect that I should be able to turn off ALL analog gain on the 5D through Magic Lantern and have roughly the same signal.

    But I don't. I can run the BeachTek's good signal into the camera, see the green lights on the BeachTek confirming that I've hit a reasonable audio level, but get all of -30db (if I'm lucky) on the camera - if not -40db of nothing.

    This doesn't make sense. If I have a confirmed good audio level going into the camera, why should it need to be boosted (by 32db) AGAIN by the camera's preamp? I realize the camera is recording in 16bit 44.1kHz instead of any better settings, but it doesn't explain a loss of 30dB in volume with no explanation.

    Any ideas?

    -Kurt

    #2
    Is is because the camera has a stereo input and your beachtek is outputting a mono signal, a computer input tends to be for a mono feed but if you are feeding mono to a stereo 1/8" TRS it could be shorting the two left and right signals out and therefore lowering the level.
    Over 15 minutes in broadcast film and tv production: http://www.imdb.com/name/nm1044352
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      #3
      I threw the computer theory out the window, for I realized its own built-in preamp was affecting the input.

      That said, the BeachTek's output is stereo.

      I'm also discussing this on the ML forums, where I just posted this discovery:

      I haven't plugged the mic directly (will try that right now), but I did wind up connecting connecting the camera's input to the BeachTek's headphone output, rather than the BeachTek's intended to-camera ouput.

      Voilą - the output impedance from the headphone jack could be matched in the camera with a bit of fiddling with the volume knob. The primitive V/U meters on the BeachTek (yes, I realize clipping is arbitrary, but it's good enough to know whether the camera should be getting a very hot signal or not) could be easily with those on the camera with no additional gain necessary. I recorded a clip and checked the audio in Adobe Audition for noise - it is clean, and what I expected given my trim settings.

      Now, I'm no great audio expert - as has been undoubtedly noted - but it seems as if the intended output jack of the BeachTek sends out a severely attenuated signal, and the headphone output gives access to the full range of the same signal.

      Any ideas?

      -Kurt

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