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-   -   Capture cards and 4 channel audio (https://www.dvinfo.net/forum/final-cut-suite/123954-capture-cards-4-channel-audio.html)

Jim Ronquest June 17th, 2008 09:36 AM

Capture cards and 4 channel audio
This I am sure is a redundant question and I do apologize.

We are needing to capture 4 channel audio into FCP. I have searched around and read some stuff on settings. But it appears the best solution is a capture card or box of some kind, I read Blackmagic and AJA quite a bit on here.

Am I on the right track with this or not.

Any suggestions are much appreciated!!

Thank you in advance for your time and knowledge.

Jim Ronquest

Mark Keck June 17th, 2008 10:55 AM

Jim, welcome to the DVI. If all you need is audio go over to the "All Things Audio" section and read thru that... there are all sorts of suggestions. If however you need audio AND video then the AJA and BM solutions are probably the way to go.

Jim Ronquest June 17th, 2008 12:26 PM

Mark, thank you for the reply!

As I read my post I realize that I was not to specific. The main reason I ask is; that I would like to capture footage shot on a XL H1 using all 4 channels of audio at the same time without going back re-capturing (1 and 2) then (3 and 4). Or be able to possibly find a deck that will handle 4 channels and capturing the source footage with audio from there.

If I am understanding correctly, which is very debatable and why I am asking if one of these cards would be beneficial to what I am trying to achieve.

Thanks again and I apologize for not being clear earlier.

Jim Ronquest

Bill Davis June 17th, 2008 01:40 PM


Be careful.

In order to capture 4 channel audio, the sampling rate typically has to be reduced to something like 32Khz instead of the standard 48Khz.

This can cause MAJOR timing issues in a typical NLE timeline. In fact, it's one of the most common causes of a picture and audio sync mismatch for people.

My advice is that if you MUST record 4 tracks, you do it on an outboard audio recorder and sync things in post.

If you MUST record 4 tracks to camera - you should re-sample all your audio back up to 48Khz before you try to incorporate it into a track expecting regular DV.

Jim Ronquest June 17th, 2008 02:15 PM

Mr. Bill, Thanks and point noted on audio "cheapening". Which also raises another question I have that may not be applicable to this forum but is relevant to the original idea.

Keep in mind I am not extremely knowledgeable on the different file types and such.

According to the XL H1's owners manual that when recording in HDV, and only using 2 channels they are recorded at MPEG1, 384 kbps, sampled at 48Khz.

When using 4 channel audio it states that they are recorded at MPEG2, 384 kbps, sampled at 48Khz. We for the most part shoot everything in HDV.

It go's on to show that when recording in DV it changes from PCM 16 bit (2 channel) at 48Khz to PCM 12 bit at 32Khz when switched to 4 channel audio.

In my simple mind it would appear that there is not as much loss in HDV as there is in DV. However I am not real sure I understand the difference between MPEG 1 and 2...
Which is why I am thinking this may work, but also why I am on here asking folks that have more knowledge than I.

For what it is worth our final output or use is in both commercial DVD sales and cable/satellite TV.

Thanks again!

Jim Ronquest

Bill Davis June 18th, 2008 01:01 AM


Here's the thing.

HDV is a method of taking what starts as a high definition picture raster (typically from a 16x9 imaging sensor at better than standard definition resolution) and then COMPRESSES it into a data stream that's almost exactly the same size as a regular DV stream.

It does this by recording whole KEY FRAMES a couple of times in each 30 frame second of video, and then just trying to keep track of the changes between those keyframes in between. (That's simplified, but essentially how it works)

When it works well, it creates a nice pleasing picture at a relatively small data rate that, yes, has more resolution than SD video. Not as much as REAL uncompressed HD - but nice none the less.

The trade off, when sit down to edit HDV, is that the computer and software has a LOT more work to do. In order to achieve "frame accurate" editing, it has to decode and re-construct all the missing frames on the fly in order to rebuild and therefore allow you to edit between frames that weren't actually stored on the tape.

Read around the board a while, and you'll see a LOT of folks having pretty big problems editing with HDV. It requires really capable software, and really solid computing horsepower in order to deal with all computational frames.

Some people have good luck and seem to have few problems working with HDV.

Other's seem to struggle mightily.

But the real issue is that neither of the delivery modes you mention will work with HDV.

At some point, some computer is going to have to take your HDV signals and re-assemble all the frames - and then you're going to have to tell your software to figure out a way to take that re-assembled stream and then transcode it into the delivery definition you want. Then THAT has to be encoded appropriately for delivery. For DVDs that means MPEG-2 authored into industry standard VOBs with the appropriate titling and authoring - or SD regular NTSC video for most Satellite and Cable stations. (Course there are Cable systems that have high-def channels - but they're built to handle real uncompressed HD, not decompressed and transcoded HDV, so I'm not sure your origination will make them very happy.)

So shooting on HDV is just the beginning of the production journey. And while the format can create lovely imagery, there are SUBSTANTIAL hoops that you need to go through in order to take this still relatively new format and deliver work originated on it into the rest of the industry.

Actually, if what you end up delivering is standard def via current DVD or to cable/satellite systems broadcasting to homes in standard def - HDV is arguably a pretty POOR way to originate - since at some point you MUST downrez and re-format your pictures to 4x3 in order to make them broadcast compatible and to display them on the millions and millions of legacy TV sets out there.

Still, every camcorder manufacturer and TV set maker has convinced everyone that HD is the great new thing.

And it is. It's just that a lot of the "in the middle of the production chain" stuff like how to conveniently edit it - keep it intact and looking good during post, and then how to distribute it in a way that keeps both the High Def crowd AND all the legacy SD folks happy is a kind of a murky picture right now.

So the bottom line is that if you're thinking about going into the HDV world to make money supplying video to commercial purposes - make sure you talk to the folks at the end of the chain who will be playing back your work.

The format and resolution and, yes, how many audio tracks are included has to make THEM happy.

Good luck.

Jim Ronquest June 19th, 2008 10:21 PM

Thanks for the information! I appreciate it!!

Thanks again!
Jim Ronquest

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