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GH4 + SD MixPre-D - what else for recording clean audio directly to cam?

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    #16
    ok, I've picked up the GH4 body, a Sound Devices mounting bracket is on order and an XL-3 cable is due for delivery,
    I tried running audio in from radio mics via the MixPre-D into the cam using a 3.5mm jack, getting clean audio with GH4 at -12db but I have to set the MixPre-D volume VERY low, is there any other settings to get me more room to play with the MixPre-D volume control - will the XL-3 cable do this?
    EVA1, AF101, AC161, GH4

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      #17
      Originally posted by TubEfingers View Post
      ...getting clean audio with GH4 at -12db but I have to set the MixPre-D volume VERY low, is there any other settings to get me more room to play with the MixPre-D volume control...
      Use the 1kHz tone generator on the MixPre-D to set volume on the GH4 to -20 dBFS. Then don't touch the GH4 for audio at all, use only the MixPre-D.

      The MixPre-D meters use the dBu scale, which is completely different than the dBFS scale used by the GH4. The dBu scale is a throwback to magnetic tape days (it's a replica of VU meters). So you're going to have to set volume on the MixPre-D like it's using mag tape. For dialog, you want your average peaks to be hitting around +8 dBu (that's not a typo, that's a "+"). That's where the red LEDs start on the MixPre-D meters. If it makes you more comfortable doing that at first, look back at the GH4 and you'll see that the +8 dBu on the MixPre-D gives you approx. -12 dBFS on the GH4, which is what you want.

      Given that the MixPre-D will start clipping at around +20 dBu (or a little higher), it's considered "good practice" to set the limiters on the MixPre-D to +18 dBu (the factory default), but some people set them a little lower. The +18 dBu on the mixer translates to -2 dBFS on the camera, so you're still not clipping the camera.

      I've set my own MixPre-D like this, and with the limiters at +18 dBu and the camera volume set using the 1 kHz tone out of the mixer, the system as a whole is practically unclippable. And the sound quality is first rate.

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        #18
        Originally posted by Bruce Watson View Post
        Use the 1kHz tone generator on the MixPre-D to set volume on the GH4 to -20 dBFS. Then don't touch the GH4 for audio at all, use only the MixPre-D.

        The MixPre-D meters use the dBu scale, which is completely different than the dBFS scale used by the GH4. The dBu scale is a throwback to magnetic tape days (it's a replica of VU meters). So you're going to have to set volume on the MixPre-D like it's using mag tape. For dialog, you want your average peaks to be hitting around +8 dBu (that's not a typo, that's a "+"). That's where the red LEDs start on the MixPre-D meters. If it makes you more comfortable doing that at first, look back at the GH4 and you'll see that the +8 dBu on the MixPre-D gives you approx. -12 dBFS on the GH4, which is what you want.

        Given that the MixPre-D will start clipping at around +20 dBu (or a little higher), it's considered "good practice" to set the limiters on the MixPre-D to +18 dBu (the factory default), but some people set them a little lower. The +18 dBu on the mixer translates to -2 dBFS on the camera, so you're still not clipping the camera.

        I've set my own MixPre-D like this, and with the limiters at +18 dBu and the camera volume set using the 1 kHz tone out of the mixer, the system as a whole is practically unclippable. And the sound quality is first rate.
        What he said! I't's exactly what you should do. Have the same combo and it works great!
        Canon C100, GH4, HPX250, HPX170, GH2, Jimmy jib lite, Portajib Explorer, Advanta jib

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          #19
          Great info @BruceWatson - many thanks
          EVA1, AF101, AC161, GH4

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            #20
            Took the new GH4 setup - Mixpre-d mounted on GH4 with SD bracket/connected using the XL-3 cable (bought from ebay, sooo much cheaper than the official Sound Devices one!) to an event in Stockholm this week,
            apart from 3 feet of snow and temperatures of minus 2 the shoot went really well and audio quality with the new setup was flawless,
            really happy with this setup and so much easier to transport than my AF100 kit on overseas jobs, thanks for all the info provided on this thread,
            I also found the "Suggestions of Motion" website really useful in terms optimizing the GH4 for video, custom settings/fn buttons etc
            EVA1, AF101, AC161, GH4

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