Thread: Audio Line Setup for Ursa Mini

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  1. #1 Audio Line Setup for Ursa Mini 
    Senior Member david evans's Avatar
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    Hi guys,

    When connecting a mic to a preamp and from the preamp to the Line in XLR connection on the Ursa Mini, what input gain do you choose on the camera? 50%? More? I tend to control input gain on the preamp (my case, the MM1), but wanted to know where to set the input gain on the camera.

    Thanks!
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  2. #2  
    Senior Member DPStewart's Avatar
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    In general practice - the input gain on the camera should be set as low as possible to minimize its own inherent noise floor.

    So set it at 25% for example then set your external mic preamp to about 80% (I personally do not often push any preamp ALL THE WAY UP unless I know from experience if that will cause distortion with that particular preamp). But DO experiment with the mic preamp at 100% to see if it remains clean. It may.

    This is a "general best practice" but if the mic preamps are generally clean on both devices then you have some leeway.
    But you always want the mic pre on the camera set LOWER than the external mic pre.
    Cameras: Blackmagic Cinema Camera, Blackmagic Pocket Camera (x2), Panasonic GH2 (x2), Sony RX100 ii, Canon 6D, Canon T2i,
    Mics: Sennheiser, AKG, Shure, Sanken, Audio-Technica, Audix
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  3. #3  
    I've used the MM1 and 302 with the UMPro and I believe I always left it at 50% @ Line Level. Not sure on the audio signal processing, but I believe anything less than that would just pad the signal (which would be a waste) and anything more would be boosting it with it's internal preamp (which you don't want). With limiters at +17dbu on the MM1, I don't ever remember clipping in camera, even with hard hits on the limiters on the MM1.

    It would be easy enough to test yourself, though. With limiters engaged and being hit on the MM1, you don't want to clip the camera at line level, but still be sending something pretty close to clipping. If you turn the camera to 25% and are hitting the limiters on the MM1 while not being close to clipping in camera, the signal is being padded down in camera, which you don't want.
    Last edited by mstrouty; 10-09-2017 at 05:49 PM.
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  4. #4  
    Senior Member david evans's Avatar
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    Thanks guys. Out of curiosity, when you have your audio recorded and put it into Resolve, how do you set audio levels? Do you trust the audio wave in Resolve and boost gain just before the wave peaks (as you would do with scopes in color correction)? This assuming I'm trying to get that clip as loud as possible just before distorting.

    Thanks
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  5. #5  
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    You guys do realize, when the UM/Pro is set to line level, the camera sets the level tp +4Db Unity level, the audio gain control does not add or rpsubtract from this. All Mic levels are then controlled by the Preamp being used.
    Cheers
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  6. #6  
    Senior Member david evans's Avatar
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    Quote Originally Posted by Denny Smith View Post
    You guys do realize, when the UM/Pro is set to line level, the camera sets the level tp +4Db Unity level, the audio gain control does not add or rpsubtract from this. All Mic levels are then controlled by the Preamp being used.
    Cheers
    Thanks Denny. Shouldn't unity gain be 0dbs? What about conforming in Resolve? Can I trust the waveform of an audio wave as shown in Resolve when I expand an audiotrack to check for distortion peaks (assuming the captured audio has no distortion). I ask this because i can have a clean captured audio that needs to play a little louder so I boost volume in Resolve. I just need to know when it starts to clip. When I'm color correcting, i trust the scopes to do that (picture wise). Can I trust the waveform of the audiotrack to do that?

    Thanks
    Last edited by david evans; 10-11-2017 at 05:52 AM.
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  7. #7  
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    My bad, I should have written +4DbV, which is voltage, at the line level. A +2DbV is 0 DB, however, most pro fest in the digital world is set to +4DbV. See below:
    ”dB-SPL is a measure of sound pressure level in the atmosphere, and is used to measure the amplitude of sounds (audio pressure waves) traveling through the air. 0dB-SPL corresponds to a sound pressure level that is barely audible to the average human. dB-SPL is also a unit, because it can be converted to other units of pressure, like pascals

    “dBFS, or decibels relative to Full Scale, is used to measure digital audio signal levels. dBFS is another dimensionless quantity, because it is just a number and cannot be converted to another unit. In a digital audio system, 0dBFS refers to the maximum signal level possible, also known as the clipping point. Therefore, dBFS values are always less than or equal to zero. -10dBFS corresponds to a signal that is 10dB lower than the clipping point of the system.

    “0dBFS (Full Scale) is the clipping point for a signal in a digital audio product. Rather than measuring from the noise floor up, digital signals are measured (or referenced) from the clipping point, or full scale, down. A 0dBFS (Full Scale) signal contains the maximum amount of digital information that can be used to represent the signal being defined.

    In any digital processor, an output driven with a 0dBFS signal should supply the full output potential of the device, anything beyond that level would be clipping the output. Biamp's digital clipping point is +24dBu. Thus +24dBu = 0dBFS on a Biamp meter. This may not hold true on other manufacturers' devices, if they have designed their products around a different clipping point.”


    So yes and no, some gear is set to +2DbV and other is set to +4DbV. As a reference, 0Db=+2DbV, as a guide. You should be able to trust the Resolve meters, and if they are a digital scale, then clipping occurs a +24Db, not 0Db, whcih is the old analog peak level,before analog distortion occurs. BM cameras are digital audio reference, as a starting point, and to allow for head room to prevent clipping, I set my 0 DB tone reference to +12Db on the digital scale.
    Cheers
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  8. #8  
    Senior Member DPStewart's Avatar
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    Good.

    Set the UM to line input and all you have to do is control the Mic Pre. That simplifies it quite a bit.
    Cameras: Blackmagic Cinema Camera, Blackmagic Pocket Camera (x2), Panasonic GH2 (x2), Sony RX100 ii, Canon 6D, Canon T2i,
    Mics: Sennheiser, AKG, Shure, Sanken, Audio-Technica, Audix
    Lights: Every Chinese clone you can imagine
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  9. #9  
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    Do any of you guys ever hear like audio is clipping in headphones, but the levels seem fine also neither receiver or transmitter on Sennheiser EW100 isn't clipping?
    I got this during some interviews, but as I remember audio file was not clipping in the end.

    Any of you experiencing same problems?
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  10. #10  
    Senior Member david evans's Avatar
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    Thanks guys, one more question. The camera always records audio in wav format, right? Whatever video format I choose (Raw, Prores 422, 444, Xq, etc), the audio is always uncompressed, correct?

    Thanks
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