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Audio dropouts

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Jeff Mack
Audio dropouts
on Dec 6, 2010 at 4:53:53 pm

Here's my workflow:

Sony Z-1. 2xlr inputs - 1 line level feed from a miver, the other is mic level to a shotgun. Audio and video out into a miranda adc800 converter (converts audio and video to HD SDI). This bypasses camera compression. Then HD SDI into IOHD (all firmware and sowftware up to date) and then into my MBP.

Control Panel set to 1080i 29.97 pro res HQ capture via VTR Exchange. This may be causing my problem. MBP specs: MBP 17 inch, 2.16 GHz with 2 GB 667 MHz DDR2 SDRAM. 500 GB internal drive.

I normally capture to an esata raid but I was lazy for this event and only needed a 1 hour capture (about 100 GB and I had 300 GB free.

The capture went perfectly during the hour. I forgot to turn off my screen saver so during the capture, I shut it off. Didn't do anything or have anything else in the background running.

When I go home and started to watch the footage, I heard random pops. I inspected the waveforms and saw dropouts randomly (Flat Lines) throughout the hour. They were random from 1 frame to up to 5 frames. Couldn't notice any rhyme or reason for why this happened. I thought it might have been a Camera issue but my local tech says I bypassed the circuitry and was only passing the audio.

I have more testing to do like taking the analog audio into the IOHD and video via HD SDI. My question is, is my MBP specs an issue. I have never noticed this with vtr exchange. I just was lazy on a setup and didn't bring the raid or a preamp for my mic. Also, both audio tracks have identical drops in the waveforms so it seems somewhere south of the camera.

Jeff


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Jeremy Garchow
Re: Audio dropouts
on Dec 6, 2010 at 10:18:19 pm

I know you won't want to hear this, but 1080iHQ to an internal drive is not so nice.

[Jeff Mack] "Audio and video out into a miranda adc800 converter (converts audio and video to HD SDI). This bypasses camera compression. "

I disagree here. You are taking the HDV feed from the camera, correct? That firewire feed is compressed already. To bypass HDV, just take the analog outs from the camera and go straight in to ioHD.

[Jeff Mack] "I thought it might have been a Camera issue but my local tech says I bypassed the circuitry and was only passing the audio. "

Might be a temporary loss of a/v sync. Was there any dropped video fames during this?

[Jeff Mack] "My question is, is my MBP specs an issue. "

You know this already, but you should really use an external drive and the minimum sys req. form AJA is a 2.33 Core2Duo:

"MacBook Pro (2.33GHz Core 2 Duo minimum), 2GB or more of system RAM, ExpressCard/34 FireWire 800 card or ExpressCard/34 Sata Controller"

Jeremy


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Jeff Mack
Re: Audio dropouts
on Dec 6, 2010 at 10:55:23 pm

Hi Jeremy, your right, I kinda knew I was pushing it with my MBPro. I did NOT capture HDV. I did use the component cable, it went into the converter which embedded the audio in a 10 bit full raster 4:2:2 stream. I do this because I need longer lenth than my cable. I set my MBP up in the corner and I use my 25 ft hd sdi cable. As I said, I was lazy this time and used the system drive to capture. Tell me, why does it matter where the data goes anyway. I never understood that. I always thought it tok the same resources either way.


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Jeremy Garchow
Re: Audio dropouts
on Dec 7, 2010 at 4:35:58 pm

[Jeff Mack] "I did NOT capture HDV."

Sorry, I did a quick search and thought that was an HDV to SDI converter. My bad on that one.

[Jeff Mack] "Tell me, why does it matter where the data goes anyway."

Data throughput. Quite simply, your system disk is doing other things besides capturing, like running applications, caching, doing all the things a system does. To simultaneously write video files to it, while it's doing those things is asking for trouble. A dedicated external drive that is ONLY having video write to it, is a faster system and therefore has way more overhead and less chance of problems.

Jeremy


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