Question about recording two channels on tape

rmack350 wrote on 3/7/2007, 5:29 PM
Maybe someone here knows the answer to this.

Just about every video interview I've ever worked on, the audio has been recorded as Lav on one channel and boom on the other. Why is it in Vegas (and evidently ppro too) when you capture clips you have to take both channels and it has to be treated as stereo?

I'm asking because in all the years we used Media100 we could always specify if we wanted audio and which channels, and we weren't forced to treat it as stereo.

Is this something to do with the way audio is encoded in DV25? And if so, are programmers just assuming you'd do it this way for other formats as well?

Seems like an oversight.

Rob Mack

Comments

Chienworks wrote on 3/7/2007, 5:44 PM
It's easy enough to Ctrl-drag the audio to a second track, then set one track to Left only and the other to Right only. So easy, it's probably not worth doing any more programming.
bevross wrote on 3/7/2007, 6:02 PM
The setup you describe sounds like it would have been initially recorded in stereo, too -- on a two channel recorder, say, with the lav on one, the boom on the other. The audio program just captures what was created. If you were recording to computer you could create the separate tracks as desired.

It's easy to split the channels in Vegas or other audio editor. In Vegas -- duplicate the stereo files, put them each on their own track. Mute left channel on one, right channel on the other (in the Mixer window -- click the little padlock on the bottom of the channels to "unlock fader channels" and pull the faders down, etc. ). Then, maybe render out each track to mono & voila.
rmack350 wrote on 3/7/2007, 6:16 PM
Wellll, yes and no. (and, yes, that's what I do)

Partly I'm wondering *why* it's this way? Is it that a stereo stream is embedded in the DV stream and it's no trivial matter to pick and choose the audio tracks to ingest?

I'm sitting here next to a guy who has, for many years now, logged shots and made choices about which audio tracks get digitized or captured (depending on the system). He's using PPro/Axio now and screaming bloody murder at adobe engineers about not being able to make choices about the audio he takes in. (I've been present for the conversation, they had blank looks on their faces).

Vegas is the same way.

So, this person is pretty adamant about not bringing in audio when he doesn't want it, or only bringing in one channel as a mono track, etc. I'd call the guy a professional user, with lots of experience going back many years to the time when Media100 and Avid were in their infancy. He looks at this inability to control how he takes in audio and feels like the software is a joke. (he's looking at PPro, but the same is true of Vegas)

I have to agree with him. It's not ideal. So I'm wondering if there's actually a good technical reason why 2 channels of audio aren't handled more deftly. Is it that the focus is on consumer video, where most users don't even own a mic, let alone have two pots on the camera for right and left channel levels?

Rob Mack
rmack350 wrote on 3/7/2007, 8:47 PM
It's a very common mic scheme on professional cameras where you can easily treat the channels as non-stereo tracks. In this case you have an xlr input for each channel, pots for each channel, meters for each channel.

Now, I don't really have a problem with just deleting the audio, adding just video from the trimmer, copying tracks to get separate tracks of audio. But it doesn't show well when you want to show off Vegas to someone who's used to more finesse in an edit system.

What I'm really wondering is if there's a technical reason in the DV format that leads Vegas and PPro to deal with audio tracks this way, or if it's just that these application's main user base is home users with consumer cameras.

Rob Mack
Geoff_Wood wrote on 3/7/2007, 11:58 PM
I assume the two tracks are capured on tape, otherwise if 'captured' (ie recorded) directly into Vegas they could of course be separate mono tracks.

Sop, the question should really be "can a the audio from a DV stream be separated out to discrete track during capture ?' . In Veags, or anywhere ?

The answer - " I haven't a clue !" .

But I can't see why it shouldn't be possible, and option on Advanced Capture, or even General ...!

geoff
Chienworks wrote on 3/8/2007, 3:40 AM
Rob & Bevross, please read my post above. You're both making this process more difficult than it has to be.
rmack350 wrote on 3/8/2007, 9:14 AM
Not really the point, Kelly. I'm not so much interested in the process of adapting to reality as I am in why something that was once a common procedure when ingesting footage now draws blank stares from a group of 6 programmers.

After thinking about it, here's what I suspect. The practice of using two tracks of audio on tape for separate microphone treatments is something you really are more likely to do with pro cameras. That's one point.

Secondly, the editors I meet who expect to be able to control what audio gets captured are coming from longer experience, specifically from long years of working with BetaCam SP.

That's an analog format. The audio isn't embedded in the video data stream because there is no such thing. So, those users either digitzed by feeding Component and 2 channels of audio into a box, or SDI and two channels of audio. They were using much less powerful systems with very limited storage and would usually capture at low data rates, edit, recapture what they needed at high data rates, render and then print to tape.

Now, I think that the *expectation* with these people is that they should be able to chose whether to take in the audio and if so, which tracks of it.

Now, here where I work we switched from BetaCam to DV but the edit system was the same (Media100). The DV deck only had SDI output so Media100 functioned the same way it had before and you could choose what audio to take. So the expectation here has continued to be that we could skip audio at ingest time.

I suspect that the reasons you don't see this as an option in either Vegas or PPro is that
1) these are largely built around DV25 which has audio embedded in the video stream. You can't just drop the audio without rewriting the stream (which SDI does anyway, but then you have to get programmers to go along with it)
2) Home users are the largest part of the market for these programs and therefore anything that doesn't address them is a low priority
3) The progammer base actually doesn't have much exposure to the professional market.

In a way I'm looking for talking points to explain to this editor friend why his new edit system isn't built to allow him to pick what audio to digitize. I certainly won't convince him that this is acceptable but I'd like to be able to say there's a good reason for it.

Rob Mack
newhope wrote on 3/11/2007, 2:07 PM
Your description of why the digitising process has developed the way it has is basically correct.

Back in the days of analogue SP the editors had to choose, mind you as an audio editor/mixer I sometimes found they hadn't had the sense to choose the correct channel so I had to go back and redigitise the audio to get the correct channel anyway. Usually this happened when the camera operator or sound recordist went non stnadard or there was a technical reason why the 'normal' channel couldn't be used. Do your professional editors ever mention that 'in the old days' they sometimes had to go back an re-digitise because they had actually chosen the 'wrong' audio track because of some technical or field operational 'glitch'?

In Vegas (sic DV) the data streams are fairly low compared to analogue or Digibeta capture via SDI etc. The audio, which is still the smallest part of the stream, really isn't causing a great deal of extra storage space, after all your going to be saving all of about 350Mb per hour of video, out of a total 13Gb Video+Audio, for single channel mono capture as opposed to dual channel and drives have become much larger and cheaper.

What it gets down to, as was clearly pointed out before, is where you choose to select the track you want.

In the analogue, SDI or Media 100, AVID world it's during capture.

In Vegas or DV it's after capture.

In Vegas all you have to do is right click on the 'stereo' audio track and select the 'Channels' submenu then either the left or the right channel. You can even combine the dual mono's (they're not stereo, they are, as you indicated, dual mono) into a summed mono track or, as pointed out earlier, CNTRL Drag to a new track to create a duplicate and then select left on one and right on the other if you want both as separate mono tracks.

It is a different way of working but so was moving from film (sprocket) editing to video, linear to non linear, analogue to digital.

As an audio editor DV capture of both audio channels in Vegas gives me the option of choosing from either channel without having to worry if the video editor has 'cloth ears' and has actually digitised the correct channel all of the time.

My suggestion is to tell your professional editors there's really is a benefit to the audio process down the chain and it's only a matter of choosing during the editing, a better time to make such a choice, rather than at the point of ingest that is different. To my mind as a professional audio operator, with thirty years of experience from sprockets to video, analogue to digital, that's a plus not a minus.

Regards

Stephen Hope
New Hope Media