simultaneous 4-channel DV audio capture: change over time and reason

[Mark Petereit]

The two-channel audio limit is a limitation of *Firewire*. As long as you’re capturing using a hardware device that supports 4 audio channels, you should be fine.

I capture HD-SDI video through an older BlackMagic HD Extreme board using Final Cut Pro’s Log & Capture and it captures 4 channels with no problems.

[Anthony Guest-scott]

Thanks, Mark.

I have read this before, but I must confess that I don’t quite understand why it would be a limitation of Firewire. I understood Firewire to be simply a vehicle for transporting data as 1’s and 0’s from one component to another. Is there some way this data is output from devices or packaged that would cause it to be limited to transporting a certain number of audio tracks?

Anthony

Anthony

[Mark Petereit]

Dunno. I learned everything I know about it reading the snippet from the user manual you included in your original post. 😀

Just curious, what hardware device are you using to capture?

[Anthony Guest-scott]

We are capturing MiniDV tapes from the Sony DVCAM/HDV deck through Firewire directly into the CPU of the MacPro, so there is no other hardware component in the chain.

Anthony

[Mark Petereit]

Sounds like you’ll definitely want to start looking for a good deal on a BlackMagic or Kona card. Or here’s a great deal on an Aja IoHD!

[Rafael Amador]

[Anthony Guest-Scott] “I have read this before, but I must confess that I don’t quite understand why it would be a limitation of Firewire. I understood Firewire to be simply a vehicle for transporting data as 1’s and 0’s from one component to another”
Yes, but you must tell the FW interface which data to transport.
This is what the Capture Presets are for.

Had you tried to duplicate and edit your DV Capture Preset?

Rafael

http://www.nagavideo.com

[Anthony Guest-scott]

Thanks, Rafael.

Yes. The audio options offered in the Capture Preset Editor allow for these options for Input (from a DV Audio device):

-First 2 channels
-Second 2 channels
-Mix 4 channels

And these for Format:

-48.000 kHz 16-bit 2 chan
-44.100 kHz 16-bit 2 chan
-32.000 kHz 16-bit 2-chan

So this interface allows one, leaving aside the question of resolution for the moment, to capture all 4 channels of audio in two separate passes, or mixed as stereo pair – but not 4 separate audio tracks in a single pass, which is what we’re after.

Anthony

[Rafael Amador]

Hi Anthony,
I’ve been Googeling about this issue but I haven’t found any solution to get that done in FC.
HOWEVER, I think that may be possible just using QT.
Switch your device on, and in QT open a “New Movie Recording”.
Before, have a look to “Recording” in the QT Preferences.
QT should be able to records whatever comes through your FW.
I think it may works, but I can not test it. No 4 channels MiniDV around.
rafael

http://www.nagavideo.com

[Anthony Guest-scott]

I appreciate you looking into this issue, Rafael, and my apologies for taking so long to respond.

You know, I have tried your suggestion of capturing directly in QuickTime Pro (7.6.6, in this case). Here is what happens:

Opening the file in QT and looking at the audio settings for the sound track under Properties shows 4 channels, with the first channel assigned as Mono and the rest described as “unused.” This is accurate when compared with the source tape. And, when dragged to a Final Cut Pro timeline, I do see 4 tracks of audio appear there.

I should not that when I play back this file (in QT or FCP), the sound plays back as dual mono instead of true mono (on the left channel) as was present on the source tape. This seems to be an issue with sound output on the computer workstation however – routing that audio through both sides of my headphones – because when I look at channels 2, 3, and 4 in the FCP Viewer, there is no waveform.

But here’s the catch…when I look at item properties for this file in FCP, it tells me that all channels were recorded as 16-bit 32 kHz audio instead of 12-bit. Furthermore, a MediaInfo report shows the following (copied below). I am not exactly sure how to interpret the audio information in this analysis. It looks like it is showing 3 audio tracks, and I am confused about how to interpret the channel information contained for each track and bit rate – some say 12, others say 16.

General
Complete name : /AHEYM_video_testing/4_channel_12bit_32k/atm_09010d04_mdv352_qt.mov
Format : MPEG-4
Format profile : QuickTime
Codec ID : qt
File size : 40.0 MiB
Duration : 10s 877ms
Overall bit rate : 30.8 Mbps
Encoded date : UTC 2010-06-25 13:40:31
Tagged date : UTC 2010-06-25 13:40:34
Writing library : Apple QuickTime 7.6.6
com.apple.quicktime.make : Apple
com.apple.quicktime.model : MacPro1,1
com.apple.quicktime.software : Mac OS X 10.6.3 (10D573)
com.apple.quicktime.creationdate : 2010-06-25T09:38:50-0400
com.apple.quicktime.player.movie : (Binary)

Video
ID : 2
Format : Digital Video
Codec ID : dvc
Duration : 10s 877ms
Bit rate mode : Constant
Bit rate : 24.4 Mbps
Width : 720 pixels
Height : 480 pixels
Display aspect ratio : 4:3
Original display aspect ratio : 4:3
Frame rate mode : Constant
Frame rate : 29.970 fps
Standard : NTSC
Resolution : 8 bits
Colorimetry : 4:1:1
Scan type : Interlaced
Bits/(Pixel*Frame) : 2.357
Stream size : 37.3 MiB (93%)
Encoding settings : ae mode=manual / wb mode=automatic / white balance= / fcm=manual focus
Encoded date : UTC 2010-06-25 13:38:59
Tagged date : UTC 2010-06-25 13:40:34

Audio #1
ID : 1
Format : lpcm
Codec ID : lpcm
Duration : 10s 877ms
Bit rate mode : Constant
Bit rate : 2 048 Kbps
Channel(s) : 3 channels
Sampling rate : 1 Hz
Resolution : 16 bits
Stream size : 2.66 MiB (7%)
Encoded date : UTC 2010-06-25 13:38:59
Tagged date : UTC 2010-06-25 13:40:34

Audio #2
ID : 2-0
Format : PCM
Muxing mode : Digital Video
Muxing mode, more info : Muxed in Video #1
Duration : 10s 877ms
Bit rate mode : Constant
Bit rate : 768 Kbps
Channel(s) : 2 channels
Sampling rate : 32.0 KHz
Resolution : 12 bits
Video delay : 666ms
Stream size : 0.00 Byte (0%)

Audio #3
ID : 2-1
Format : PCM
Muxing mode : Digital Video
Muxing mode, more info : Muxed in Video #1
Duration : 10s 877ms
Bit rate mode : Constant
Bit rate : 768 Kbps
Channel(s) : 2 channels
Sampling rate : 32.0 KHz
Resolution : 12 bits
Video delay : 666ms
Stream size : 0.00 Byte (0%)

Menu
ID : 3
Encoded date : UTC 2010-06-25 13:38:59
Tagged date : UTC 2010-06-25 13:40:34
Bit rate mode : CBR

Anthony

[Rafael Amador]

[Anthony Guest-Scott] ” should not that when I play back this file (in QT or FCP), the sound plays back as dual mono instead of true mono (on the left channel) as was present on the source tape.”
In a digital file, the mono channels are not assigned to the left or the right as they were recorded on camera. I mean, if you play a QT file with Mono channels, you will get the same output through both loudspeakers. You may “pan” the channels when you mix to stereo, or you may route those channels when you are printing to tape.
rafael

http://www.nagavideo.com