4 channel Audio via SDI?

[Daniel Kohl]

I noticed that Canon has gone even further in making it possible to record professional four channel audio on the XL H1, by adding independent level controls for all four audio inputs. Does that mean that it is possible to capture all four audio channels as separate tracks in a one capture pass using our NLE programs?

Up until now, this feat has not been possible using the FW port, since FW apparently only allows for delivery of one stereo pair.

One possibility would be that the SDI jack on the XL H1 delivers audio as well as uncompressed video. FCP can, For example, capture multiple audio tracks with the right SDI hardware.

Can anyone comment on that?

[Chris Hurd]

Hi Daniel, unfortunately the SDI output on the XL H1 carries video only -- no audio at all.

[Daniel Kohl]

Thanks for your reply Chris,

Is there any idea from the side of Canon as to how one would work with the four channels of audio created by the XL cameras?

Apparently they have put a lot of thought into this nice functionality of the cameras - at least hardware wise.

Do you, or anyone else, know how Canon suggests users to capture the four audio tracks into their NLEs?

[Peter Ferling]

This also concerns me... I still can't find an answer on the audio out. It would be a disadvantage, even for 4 channels, if the audio goes through the mpeg layer II compression, and we cannot access it as PCM otherwise.

Pete

[Chris Hurd]

If recording in HDV to tape, the four audio channels are each 16-bit, 192kbps, Mpeg 1 Layer II.

Two channel recording to HDV is 16-bit, 384kbps, Mpeg 1 Layer II.

[Daniel Kohl]

Originally Posted by Peter Ferling

and we cannot access it as PCM otherwise.

What is PCM?

[Barry Green]

Pulse-Code Modulated. In everyday use here it means "uncompressed".

[A. J. deLange]

PCM is archaic terminology from the early days of digital communication. A voice channel was sampled and converted into a digital value such as 66 which was then represented as a binary number (66 = 01000010) which was modulated onto a carrier by turning it on (putting out a pulse) for each 1 and not turning it on for a 0 (no pulse). Each sample level corresponded to a unique pulse code. Hence Pulse Code Modulation. Today the carrier is as likely to be shifted in phase or frequency with or without simultaneous amplitude shift but it's still called PCM. In video parlance this is (or was) done mainly to distinguish it from FM (frequency modulation) - the most popular means of recording sound on video tape up to the point where PCM recording appeared.

[Peter Ferling]

Maybe I should say, I like the 16bit 48KHz stereo audio I get from the XL1s, but now I'm faced with mpeg1 layer II from the H1, and find it difficult to believe that is somehow better? Not. Either I'll have to re-encode the audio to PCM, or capture audio via another means, and then sync in post.

Of course, I'll have to sample the quality of the audio, to see if 384kbps is just as good a quality (and still face an additional conversion, and resync to the SDI capture).

Pete

[Daniel Kohl]

Thanks guys,

I actually understood that.

What I don't understand, is why would the audio be compressed Mpeg layer II (which is mpeg2, right?). It's not like the HDV is creating a muxed DVD when it records to tape or HDD over the FW bus? Is there no longer a video and an audio track on the tape?

Sorry Chris you did write Mpeg 1 layer II

[Daniel Kohl]

Originally Posted by Peter Ferling

Of course, I'll have to sample the quality of the audio, to see if 384kbps is just as good a quality (and still face an additional conversion, and resync to the SDI capture).

Pete

I think I'm going to be ill....

[Peter Ferling]

Originally Posted by Daniel Kohl

I think I'm going to be ill....

Ah well. I think we're getting over the initial excitement of these HDV camera's and learning just exactly what limitations they bring to the table. We are spoiled by what our current crop of DV camera's have provided, and at 1/5th the cost of comparable SD camera's. We obviously will not see a repeat when comparing HDV to HD. It's not really just technology, it's now all about compression, (That includes audio as well).

If I stay in SD land, then HDV seem's like bargain, and for the next few years I can make it work. However, I'm facing the reality that I'll need to spend $40K or more to really get there. The field is too new yet to really tell. I'll have to get my hands on the H1 and see what $10k will give me...