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Free AC3 encoding workflow

Oct 24, 2009 3:16 AM

 

Like most of you, I was annoyed to find out I couldn't create AC3 surround sound files with my CS4 software, and also that we got downgraded from Audition to Soundbooth.  We all paid a lot for it! I know many people have ranted about that already, so enough said.

 

Here is a workflow that gets around that problem without ponying up for the SurCode Plug-in, and/or buying Audition!

 

 

To convert your mixed 5.1 audio, or stereo audio, to the DVD standard AC3 file that Encore wants, download the latest version of Audacity here: http://audacity.sourceforge.net/  It is available for Mac OS X, Microsoft Windows, GNU/Linux, and other operating systems.  If you don't know already, it's free!

 

Now, before I start getting flamed, about Audacity, it works great!  The UI is not the most modern, but the quality is top-notch.  I've used it for years and most complaints about it are unjustified.

 

You'll need to download the latest version: "Beta: 1.3x - for advanced users."  There will soon, I hope, be an Audacity 2.0 stable release. Until then, use the Beta release for this workflow.

 

 

Note:  I'll focus on Premiere Pro CS4, because that is where I originally troubleshooted this, but something similar will work for the other Adobe products that use sound.

 

 

Workflow:

 

Create your mixed 5.1 surround sound audio in Premiere, and output the audio only by going to File > Export > Media, and selecting "Windows Waveform" as the output.  You should only have "Export Audio" checked.  Verify the format in the Summary section.  You should see something like: 48000 Hz, 5.1 Surround, 16 bit.  Now under Audio codec, make sure "Uncompressed" is selected.  Click Okay, and Adobe Media Encoder should launch.  Click "Start Queue" and your audio file will be created.  You'll get an interleaved 6 channel wave file.  Not all applications will open it, but Audacity will. 

 

Note:  When you mix your surround sound in the Audio Mixer, you'll place your little "Puck" where you want the sound to come from.  Picture yourself in the middle of the "dish," if it's a puck, isn't it in a rink, as in hockey rink...ah, but I digress.  Anyway, you'll notice that volume meters in the 5.1 (6 channel) Master section are laid out in the following order: L,R,LS,RS,C,LFE.  Also, if you open a 5.1 audio file in the Source panel, you'll see the same order from top to bottom: L,R,LS,RS,C,LFE.   Soundbooth also does it that way.  Ahh....Adobe...nice try. 

The actual channel order should be L,R,C,LFE,LS,RS.  That's the order that you'll probably have to assign in the "Audio Output Mapping" section in the properties menu to get your channels to play correctly with your surround sound hardware.  L,R,C,LFE,LS,RS is also the order that interleaved files use.  So after you create your 5.1 file, and open it in another audio program that displays them in the "proper" order, like Audacity, you'll see your tracks laid out from top to bottom in that order.  I'm not sure why Adobe does it that way, but oh well.

 

 

Surround sound primer: 

 

The LFE channel is not, despite popular misconception, a subwoofer channel.  Bass from all the channels in a surround sound Amplifier is summed and sent out to the Subwoofer.  The LFE channel is supposed to be used only for very low frequencies, to create extra  ...oomph.  I think that is the technical term.  It is not supposed to be used for bass frequencies from the other tracks.  It is for explosions, dinosaur footsteps, ...etc. 

 

Audacity will open DVD ".vob" files, and even let you select which stream (usually Language) to open.  As an example, open up a movie with some action in it like Ironman (The movie starts at "VTS_03_1.vob") and look at the LFE channel.  It's the 4th track from the top in Audacity.  You'll see it's silent except at parts where there is thumping AC/DC music at the Intro, or explosions.  It's not used as a subwoofer channel!   

 

With that in mind, you may have noticed, unless I'm missing something, that there is no way in the Premiere Mixer to assign an audio track only to the LFE channel.  Sure, you can dial up the "Bass Clef" knob to 0.00 db, and send a mono channel's audio to the LFE channel, but there is no place to put the "Puck" that only outputs to LFE.  There is one for the center channel, but without someplace to put it, your 40 Hz dinosaur footprint "Thump" is going to also be assigned to some of the other channels.  Which channels depends on your "Puck" placement.  This is not correct.  Again, unless I'm missing something, Adobe needs to correct this oversight.  We'll get back to this problem with a solution later, but first let's continue with the AC3 issue.

 

At this point you should have your wave file.  If you want to apply any global changes to all 6 channels, you can open it in Adobe Soundbooth and trim the beginning or end, and apply effects to the entire file.  You cannot, however, make changes to individual channels.  Audacity will!  We'll get to that later.

 

 

Encode with Audacity: 

 

Install the software and go to Edit > Preferences > Libraries, and click on "Download" for the "FFmpeg Library."  This is the library that Audacity will use to create the .AC3 file.  Once installed, the library version should show up next to "FFmpeg Library Version" While the "Audacity Preferences" window is still open, select "Import/Export" and select "Use Custom Mix", this is used to export a 5.1 channel file.  Now you're ready to open your .wave file from Premiere.  Drag and drop it in the Audacity workspace and you should see 6 mono tracks laid out from top to bottom in the following order: L,R,C,LFE,LS,RS.  Audacity will let you edit the individual tracks, unlike Soundbooth, thanks Adobe.  But for now, we'll keep it simple.  Set your "Project Rate" in audacity in the lower-left corner to what you want the AC3 file to be.  For DVD, chose 48000 (Hz).  If you leave it at 44100 (Hz) Encore won't import it. 

 

Your almost done.  Now let's export the file.  Go to Files > Export... > and select "AC3 Files (FFmpeg)" in the "Save as type:" drop-down.  Click the "Options..." button and set the "Bit Rate:" for your file.  For 5.1 AC3 audio, probably 448.  Now enter a file name and click "Save."  This will open the "Advanced Mixing Options" window.  This allows you to re-map the tracks to a different channel order.  It should be correct, and it should show "Output Channels:" set to 6.  Press "OK" and you're done.

 

Presto, you have a 5.1 channel AC3 file.  Use that in Encore, or whatever DVD creation program you use, and when you play your DVD you'll have full 5.1 audio coming out your surround sound Amplifier.  That is if you have one.

 

 

Test your file:

 

If you want to test your file, you can do a couple of things.  Since Soundbooth and Adobe  Bridge won't even open AC3 files, and Encore will open but only play the Left and Right channels in the preview, you'll have to either import the file into Premiere, or use another media player.

 

If you got Premiere to play your surround properly, then you can drag and drop the file into the "Project" panel and preview it from there. You will hear all 6 channels in the correct speakers, but I did notice that the quality is not very good.  Maybe Premiere doesn't decode AC3 all that well.  I heard some crackle that isn't in the file.  How do I know it isn't just a bad encoding job by Audacity?  Because I played the file with the VLC media player, and Cyberlink PowerDVD on the same computer, and also on a DVD in my home theater system with no artifacts.  Maybe Premiere doesn't decode AC3 files well. 

 

The VLC player, will play almost any file in the known universe, and at least on my computer, it automatically played the AC3 surround file, created by Audacity, with all the channels mapped correctly.  That's right, full surround out my speakers with only default settings.  It's a great player.  Get it for free here: http://www.videolan.org/

 

 

Test with Encore:

So far so good. Now open Encore, drop the AC3 file in an empty project, throw it on a Timeline and build the project without Video,  It will autoplay without a menu this way. If you set the End-Action to the same AC3 file it will repeat continuously.  Either burn this to DVD-RW and test it in your DVD player, or better yet, Build the project to a DVD Image instead, and mount it in a virtual DVD   Drive with a program like "Virtual CloneDrive."

 

If you don't know what that is, or how to do it, it is very simple.  Go to: http://www.slysoft.com/en/ and download "Virtual Clonedrive."  It is free.  It tricks your operating system into thinking you have another physical DVD drive.  In fact, it can create up to 8 virtual drives.  Now you don't have to waste time burning, and erasing DVD's every time you make a change to a project.  You can build your project as a DVD Image from Encore, save the .iso file to your Desktop and "mount" it (load it) in Virtual Clonedrive.  You're computer will now think you loaded a DVD into a physical drive, and launch whatever DVD player you have installed.  Mine launches "Cyberlink PowerDVD" which plays the AC3 audio-only DVD in full surround sound on my computer. 

 

Building and testing projects this way will save you endless hours.  If you need to make a quick change, just "Unmount" the .iso in Virtual Clonedrive, rebuild your project to the same filename, and "Mount" it again.  Instant testing!

 

 

 

Now, as promised, back to that LFE Channel problem with Premiere that I mentioned:

 

Audacity will let you modify the individual channels in your interleaved 6-Channel file.  So don't put anything in that channel in your Premiere mixer. Leave the "Bass Clef" knobs at full CCW position ( -00 db ).  The bass from the other channels will go to your subwoofer automatically in your Amplifier.

 

 

Now if you have some low frequency effects files, open them in Audacity.  You can open multiple instances of Audacity at the same time by going to "File > New."  Then, copy and paste them into the LFE Track at the correct point.

 

Audacity newbie Hint:  Audacity doesn't yet have a "Mix-Paste" function, so to avoid altering the track length as you paste in your clips, do the following: Select the LFE track by clicking on it's info area.  The info area should say something like "Mono, 48000Hz"  Then press "Delete," That will remove everything from the track.  Now copy and paste your clips into the track by clicking once with the "Selection Tool" where you want the clip to start, and selecting "Edit > Paste."  If you need to fine tune the position of the pasted clip, use the "Time Shift Tool" to move it left or right.  If you work from left to right, then you won't push clips over when you paste new ones in.

 

There is another way to do this by opening up new tracks, using the "Mix and Render" function, and re-ordering the tracks to maintain the L,R,C,LFE,LS,RS channel order.  But that's for advanced users.

 

 

Where to get thumpy effects?:

 

Remember, Audacity will open DVD ".vob" files.  Just remember to get permission from the copyright owner.  HeHe.

 

 

PS If you can't get your surround sound to work with Premiere on your computer, see my other tutorial.

 

 

 

 

 

 

 

 

 

 

 

 

 
Replies
  • Currently Being Moderated
    Oct 24, 2009 1:39 PM   in reply to Terrachild

    Thank you for the article. I was unaware of the FFmpeg addition for Audacity.

     

    For folk without Audition, I strongly recommend this little program. You have now taught me a new trick with it.

     

    As I use Audition and the SurCode AC3 plug-in, I had really not explored other possibilities.

     

    You are correct that PrPro will "garble" the order of the discrete files in DD 5.1 SS. I have never found a reason for this, and keep a conversion chart taped to my workstation's monitor. Still wonder about that channel order, but just workaround it.

     

    I end up doing similar for work with the Minnetonka SurCode DTS encoder, and Export as .WMA (discreet 6-channel files enclosed). That file goes to Audition, where I break it apart, re-order the channels and then Export from Audition as six separate, discrete mono Audio files for use in the DTS encoder. BTW - Audition will allow one to fully manipulate the LFE, as is needed.

     

    Thanks for posting, and for the tip on the FFmpeg module for Audacity.

     

    Hunt

     
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  • Currently Being Moderated
    Oct 25, 2009 1:44 PM   in reply to Terrachild

    Terrachild,

     

    Just wanted to say thank you!

     

    For someone like me who use ordinary stereo most of the time, and have felt a bit "scared" to use up the three free tries for "playing with 5:1", your post is great news!

     

    Dag

     
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  • Currently Being Moderated
    Oct 29, 2009 6:14 AM   in reply to Terrachild

    Big up!

     
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