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 Post subject: capturing digital audio from LD's w/the 2144-audio sped up
PostPosted: 17 May 2018, 00:17 
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For laserdisc preservation I'm trying to capture the video and audio simultaneously and I'd ultimately like to capture the digital pcm track. Currently using a Blackmagic Intensity Shuttle usb 3.0 as the capture device but strongly considering a pci/e card. When I capture the digital audio, the audio is sped-up on the raw file. Doesn't happen when I capture analog audio. It also does not happen when I capture digital audio from a dvd player. I've got the s/pdif set to "Basic" as the manual says for anything older than 2005. Only difference between laserdisc and dvd audio is the quantization (44.1k vs. 48k). I doubt it matters if it's pcm vs. ac-3?

The quick start sheet does recommend a 6' or longer 4K rated hdmi cable. Currently I'm using a cheap, 3" non-4K cable from the 2144 to the Shuttle. Below is the quote.

"NOTICE: hdmi cables should be at least 6 foot long. Shorter cables can cause issues due to hdmi cable equalization in the transmitter and receiver." For Radiance 2144 units, Lumagen recommends the use of 4K rated hdmi cable on both Radiance outputs. This is due to the 4K output chips used having faster edge rates that demand better cables (even outputting 1080i or 1080p)."

Is this my problem? 4K cable?
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 Post subject: Re: capturing digital audio from LD's w/the 2144-audio sped
PostPosted: 17 May 2018, 02:06 
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So by “sped up” do you mean it finishes before the movie or does it just sound like a higher pitch?

Btw, no the cable is not the issue.
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 Post subject: Re: capturing digital audio from LD's w/the 2144-audio sped
PostPosted: 17 May 2018, 02:13 
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signofzeta wrote:
So by “sped up” do you mean it finishes before the movie or does it just sound like a higher pitch?

Btw, no the cable is not the issue.


Yes to both; the audio pitch is higher and the audio ends before the video. Say a one minute clip the audio would end about 54 seconds in.
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 Post subject: Re: capturing digital audio from LD's w/the 2144-audio sped
PostPosted: 18 May 2018, 04:06 
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clashradio wrote:
Yes to both; the audio pitch is higher and the audio ends before the video. Say a one minute clip the audio would end about 54 seconds in.


Since the Radiance is only multiplexing the audio as it goes and not meddling with it in any way, I would say the problem is probably on the capture software side. Any options/settings there for fps, KHz, sync, etc.?

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 Post subject: Re: capturing digital audio from LD's w/the 2144-audio sped
PostPosted: 18 May 2018, 16:37 
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Yeah, it’s all in the rendering of the video. Analog data can never have real time lag because there is nowhere in the system to store it. The only way audio and video can go out of sync is if one is being rendering into the file at a different rate than the other. I’ve seen this before but without knowing your exact setup I can’t say what the fix is. I’ve fixed it by messing with the sample rate but LD audio is just CD audio so it should be the most standard settings possible. I suppose it also possible than the video is being rendered too slowly but you said you could hear the audio is pitched up so probably not.

I would imagine the sample rate is too fast in the settings? Like if you rendered a 48kHz file using data from a 44.1kHz bitstream the exact phenomenon you’re describing would occur.
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 Post subject: Re: capturing digital audio from LD's w/the 2144-audio sped
PostPosted: 18 May 2018, 21:59 
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There are no audio setting options in Media Express, which is the capture software for the Shuttle, and probably all of Blackmagic's products. But I can select which frame rate to capture at depending what the output of the 2144 is set to. Doesn't matter if I capture at 480p, or 1080i, same problem (only with digital audio capture of 44.1k).

And when I say there are no audio settings in Media Express, I don't like that the captured files are at 24b/48k. You can not capture audio at 16b. At first I was wondering if this was the problem, but that wouldn't explain why I don't have the sync issue with analog audio.
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