Latest post Thu, Jul 5 2018 10:43 PM by Krishius. 11 replies.
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  • Wed, Jul 4 2018 2:56 PM

    • Krishius
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    Nitris DX HW Calibration - does it affect capture from tape?

    Hello!

     

    If I'm capturing video/audio from tape source connected via a Nitris DX box, does the HW Calibration setting (under Audio Project/Hardware) influence the incoming audio signal levels from SDI, analog XLR, AES/EBU or RCA inputs? Or do the incoming levels remain the same regardless of the Calibration setting?

     

    Thanks in advance!

  • Wed, Jul 4 2018 5:17 PM In reply to

    Re: Nitris DX HW Calibration - does it affect capture from tape?

    Analog audio I/O.

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  • Wed, Jul 4 2018 8:34 PM In reply to

    • Krishius
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    Re: Nitris DX HW Calibration - does it affect capture from tape?

    Thanks!

    So is it true that when I'm in PAL project and capturing from a PAL analog deck, this setting should be set to -18, since in PAL world alignment levels are -18 dBFS?

  • Wed, Jul 4 2018 8:50 PM In reply to

    Re: Nitris DX HW Calibration - does it affect capture from tape?

    Krishius:

    Thanks!

    So is it true that when I'm in PAL project and capturing from a PAL analog deck, this setting should be set to -18, since in PAL world alignment levels are -18 dBFS?

    Dpends on how the deck is calibrated, and the type of meters on the deck. Some Beta decks for instance had VU meters (PVW, UVW), some had PPM meters (PVW), and their output boards can (and should) be calibrated.

    ALso, the -18dBFS alignment level you mention is a digital one, so that does not apply here. Calibration means setting the relation between analog and digital levels.

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  • Wed, Jul 4 2018 9:04 PM In reply to

    • Krishius
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    Re: Nitris DX HW Calibration - does it affect capture from tape?

    What would be the right way to go if I have no idea how my playback machine has been calibrated? I believe it's set to factory defaults. In my case it's S-VHS Sony SVO-5800P deck with it's balanced XLR audio outputs connected to Nitris DX analog XLR inputs. Should I leave the HW Calibration settings to -20 dB, or change to -18 and find someone who could do the calibration?

    So far my Nitris have never been calibrated in any way - I have not done anything in Calibration Window. The only thing I've tried is switching HW Calibration from -20 to -18 and back with no additional adjustmens.

  • Wed, Jul 4 2018 9:51 PM In reply to

    Re: Nitris DX HW Calibration - does it affect capture from tape?

    Are there any test signals on any of your source tapes? You would need to start by checking the voltage coming out of the SVO when playing back a reference tone.

    Another idea would be not to worry too much about it, and adjust levels inside MC after capture if needed. Or are you seeing dangerously high levels coming in?

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  • Wed, Jul 4 2018 10:09 PM In reply to

    • Krishius
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    Re: Nitris DX HW Calibration - does it affect capture from tape?

    Thanks for helping!

    The tapes contain original camera footage and have no bars and tone anywhere on them. Also I see no dangerously high audio levels coming in - everything looks more or less fine. I’m capturing these tapes (a lot of them) for as high quality as possible archiving so i wanted to be sure I’m doing everything right.

     

    I’m curious what happens in case I only change HW Calibration setting from -20 to -18 but do not perform any further modifications in Calibration window? Does doing so actually impact the incoming signal level somehow?

  • Wed, Jul 4 2018 11:17 PM In reply to

    Re: Nitris DX HW Calibration - does it affect capture from tape?

    I've never calibrated a Nitris DX, only Meridien boxes, so I daren't say for sure how it works on Nitris DX.

    That said, the theory is this:

    1. When you play back a reference tone of a certain level from the deck, its analog outputs will output a certain voltage.

    2. When you feed an analogue signal into your Nitris DX, its A-to-D converters will convert a specific incoming voltage to a specific digital value, which is a matter of calibration.

    3. And when playing back something from MC, the Nitris DX's analog outputs will emit a certain voltage for a certain digital value, again a matter of calibration.

     

    #3 is mostly relevant when outputting to tape, otherwise usually not much.

     

    I hardly dare go into the numbers for #1 and #2, as I'm not 100% sure about them. But back in the days in Holland, we used -9dB PPM, which we would line up with -18dBFS (and we used -3dBVU on decks with VU meters IIRC). I _think_ that was following German ARD/ZDF standard. With a maximum mix level of 0dB PPM (which I think equalled +6dBu or 1.55 Volts), and that gave us around 9dB of additional headroom in the digital domain (so up to +15dBu). And that would imply the -18dBFS/-9db PPM calibration level would equal -3dBu, 0.55 Volts.

    I think EBU standard is 0dBu = -18dBFS, so that would be 3dB more headroom, or 18dBu.

    I _think_ the US SMPTE specifies +4dBu = -20dBFS (and 0 VU), which would give headroom up to 24dBu.

    So _if_ your SVO is calibrated to the ARD/ZDF standard, it would play back a calibration tone at -9dB PPM and output it as -3dBu at 0.55V.

    And if your NDX is calibrated for +4dBu = -20dBFS (1.23 Volts), the 0.55 Volts from your deck would come in at -27dBFS

     

     

     

    If these are camera tapes, you'll just need to choose the standard by which you choose to convert the analog to digital. If you use 24bit audio, that gives you the best signal-to-noise ratio.

     

    Krishius:
    I’m curious what happens in case I only change HW Calibration setting from -20 to -18
    To the best of my knowledge you are thereby telling the NDX box to either make +4dBu come in digitally as -20dBFS or as -18dBFS (whereas I think our ARD/ZDF calibration would have that at -11dBFS and EBU would have that come in as -14dBFS).

     

    Above all, I reserve the right to be wrong about these numbers, though.

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  • Thu, Jul 5 2018 11:36 AM In reply to

    • Krishius
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    Re: Nitris DX HW Calibration - does it affect capture from tape?

    Thanks for in-deep explanation!

     

    I did some testing:

     

    I captured the same ~10 minutes long bit off a VHS HiFi audio track twice: first time with HW Calibration set to -18 and second time with -20. No addtional adjusments were done. Then synced both clips and exported as two stereo wave files. Then compared both files in Adobe Audition by scanning amplitude statistics.

    The results look practically identical for both files. Apart from the fact that analog audio has some tiny differences each playback time, there was no 2 dB difference in overall level I expected.

     

    Here are the Amplitude statistics mesurements for -18 version:

    Left Right

    Peak Amplitude: -9,75 dB -9,20 dB

    True Peak Amplitude: -9,74 dBTP -9,20 dBTP

    Maximum Sample Value: 2677006 2740486

    Minimum Sample Value: -2731122 -2909073

    Possibly Clipped Samples: 0 0

    Total RMS Amplitude: -31,01 dB -27,06 dB

    Maximum RMS Amplitude: -17,21 dB -15,43 dB

    Minimum RMS Amplitude: -103,96 dB -102,95 dB

    Average RMS Amplitude: -38,11 dB -34,11 dB

    DC Offset: 0,00 % 0,00 %

    Measured Bit Depth: 24 24

    Dynamic Range: 86,74 dB 87,52 dB

    Dynamic Range Used: 83,70 dB 85,05 dB

    Loudness (Legacy): -26,94 dB -22,75 dB

    Perceived Loudness (Legacy): -22,26 dB -20,47 dB

    ITU-R BS.1770-3 Loudness: -24,46 LUFS

     

    0dB = FS Square Wave

    Using RMS Window of 50,00 ms

    Account for DC = true

     

     

    And here are the results for -20 version:

    Left Right

    Peak Amplitude: -9,71 dB -9,60 dB

    True Peak Amplitude: -9,71 dBTP -9,60 dBTP

    Maximum Sample Value: 2674124 2743981

    Minimum Sample Value: -2742750 -2776164

    Possibly Clipped Samples: 0 0

    Total RMS Amplitude: -30,98 dB -27,03 dB

    Maximum RMS Amplitude: -17,18 dB -15,38 dB

    Minimum RMS Amplitude: -104,83 dB -103,21 dB

    Average RMS Amplitude: -38,09 dB -34,07 dB

    DC Offset: 0,00 % 0,00 %

    Measured Bit Depth: 24 24

    Dynamic Range: 87,64 dB 87,83 dB

    Dynamic Range Used: 83,70 dB 84,90 dB

    Loudness (Legacy): -26,97 dB -22,70 dB

    Perceived Loudness (Legacy): -22,21 dB -20,50 dB

    ITU-R BS.1770-3 Loudness: -24,44 LUFS

     

    0dB = FS Square Wave

    Using RMS Window of 50,00 ms

    Account for DC = true

     

    Seems like changing the HW Calibration setting alone does not affect how the Nitris DX hardware works. Or am I not getting something?

  • Thu, Jul 5 2018 5:45 PM In reply to

    Re: Nitris DX HW Calibration - does it affect capture from tape?

    It may very well only be a setting that changes the correlation between the FSD and VU meters inside MC. It would need to be set to match the physical calibration of the audio I/O (if possible, used to be possible on Meridien).

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  • Thu, Jul 5 2018 5:49 PM In reply to

    Re: Nitris DX HW Calibration - does it affect capture from tape?

    I think the key with analogue captures is to ensure the audio level feeding in to the hardware is at the right level to have eneough headroom to prevent clipping but no more than's needed or you risk adding noise. 

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  • Thu, Jul 5 2018 10:43 PM In reply to

    • Krishius
    • Top 500 Contributor
    • Joined on Wed, Oct 10 2007
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    Re: Nitris DX HW Calibration - does it affect capture from tape?

    And do I understand it right that for digital audio inputs (SDI, AES/EBU, Firewire) HW Calibration setting and anything set in Clibration window is non-relevant?

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