12 bit AND 16 bit
 

I am not sure if this post belongs here or in the NLE or audio forums, but since my experience pertains to the XL2....here goes. I bought Greg Salman's Ultimate Guide to the Canon XL2 DVD the day it became available and have found it indespensable for learning about my new camera.

So far, I have only recorded in 16 bit audio with this camera, but plan on using 4 channel 12 bit for a series of upcoming events to combine sound input from multiple mic sources while onsite at events.

Greg indicated on the DVD that it is a big mistake to try to combine 12 bit with 16 bit audio on the same project. From the beginning of the project, choose one and stick with it for the duration of the project. I will have a couple of extra 'pickup' cameras on site for additional angles from which the audio 'MIGHT' be utilized, and I don't mind downshifting these cameras to 12 bit also for the project - but here is my question...

What exactly would be the detrimental effect from combining multiple bit audio into a single project?

I remember when I had my first go'round with iMovie, I think I ended throwing in all sorts of audio clips from all kinds of sources, including AIFF, mp3, AAC and a few lower grade quicktime audio formats. I don't know for sure if they were different bit rates but I assume they may have been considering the variation of sources....but everthing played together nicely...and iMovie is not terribly advanced.

I what ways can I expect foul ups from mixed bit audio in a single project?
-Jon

Just convert any 12 bit tracks to 16 bit before importing them for editing. Edit software does not respond well to changing bit rates on the audio track -- it is easy enough to convert any errant material to avoid that situation.

If you must use the lower quality 12 bit to gain the extra tracks, just convert it after for use in the project.

Voila.

GB

Geoff Baker wrote...

<< Edit software does not respond well to changing bit rates on the audio track >>

And that's Greg's whole point in his tutorial as well. Thanks,

How would you go about converting the audio to 16bit?

Pretty much any sound editing software has the capability to save a file with a different bitrate. Even crappy Windows Sound Recorder can do this. Obviously, a more intensive application like Adobe Audition or Sony Sound Forge will give you more customizability, but even a small freebie program will probably work.

Open a project, import the clip with 12 bit audio, export the clip with 16 bit audio.

That's the easiest way to do it, and depending on your edit software may be a good way to do it. Some software is better than others (better=higher quality) when it comes to audio manipulation, so do a check of your software to see if it does a decent job. The conversion from 12 bit to 16 bit should be rock solid simple -- much cleaner than a sample rate conversion -- but some users have argued that Premiere didn't do the best job of it, for example. When I used 12 bit audio with the VX1000 the transfer software of the day used to convert the audio to 16 bit during transfer & all seemed good to me ...

It isn't hard to do, is the point, and you should have no problems.

GB

Converting audio
 

Thanks Chris and Jeff. I guess it would be easy enough to convert the audio bit rate - so if I am faced with that, I think that is what I will do so that I could keep the other cams in 16 bit and that way if I need to use their audio, that is always an option and they would be about as good as they will get. Good tip Geoff, I appreciate it.

What I was originally curious about is what the results would be if I did combine them. With Geoff's tip, I realize I woud not need to as changing the bit rate would be easy, but what would happen if I did not.

Would the software crash? Would it give audio out of sync? Would it distort or be jumbled. No big deal, just curious if someone has tried it and found out why it is a bad thing.

As far as Kevin' question - I will refer it back to my original iMovie process. If I needed to convert bit rate while using iMovie, I would select the clips in the timeline, choose 'share' from the file menu and select expert settings. If I have Quicktime Pro, I would be given a list of several options, and would probably choose 'movie to aiff' with the appropriate bit rate option I want. I would then export the sound file to the desktop and when it was done I would drag it back into the iMovie project and sync it up with the video track. (I would disable the original video track after making certain they were synced. That is just a quick cursory way of what I suspect would be a simple way to convert using iMovie. Higher end editing software also have more advanced audio features for such control.

I guess problems vary by software -- in Premiere, the best description is that performance is 'erratic'. Some users swear no problems at all. Others report sound drops or bleeps at bit rate transitions. Some exports to compressed audio formats might result in system freeze ...

In other words, not worth the worry given that the solution is simple enough.

Cheers,
GB

Thanks guys. I'm Using Premiere Pro and Sound Forge and wasn't familiar with the conversion process. Wasn't sure if I would export the audio only and resync or if I could export the footage with only the audio being converted without an added generation of video compression. Many thanks.

I plan on doing some testing with my XL2 using the onboard mic with a shotgun going into XLR in 12bit mode in the next 2 weeks (still need to get a shotgun, ME66/AT825, decisions, decisions).

If you export DV from Premiere without applying a filter there is no recompression to the video -- the only time recompression is done is if you apply a filter, use a transition ... or forget and have the 'recompress always' box checked!

GB

Jonathon,

Thanks for the tips and reminder on Greg Salman's Ultimate Guide to the Canon XL2 DVD, just ordered it. Came across it a while back but forgot about it as I just got my XL2.

Kevin

<<<-- Originally posted by R Geoff Baker : The conversion from 12 bit to 16 bit should be rock solid simple -- much cleaner than a sample rate conversion -- -->>>

I would recommend to do a sample rate conversion at the same time, preferably with a decent tool like Sound Forge. Otherwise you would be mixing 32KHz and 48KHz audio in the same project and at least one of these would be subject to sub-optimal SRC.

Nowadays, with NLEs like Vegas, the conversion from non-linear 12 bits to linear 16 bits is done automatically, and the SRC results will be OK, but Sound Forge is still better.

Richard