AC3 MP3s? Moving to internet delivery of surround mixes

1980, the cd is born, from this emerging technology, a generation is designed, a generation that will culminate in IPods, Napster, a music industry reeling from file sharing, and fans of music pleased as punch that they can go online and download any track they want. But what happened to quality? We’ve stalled, haven’t we… We started with vinyl, moved all the way forward into the brave new world of digital audio, and then took a great big leap backwards with MP3’s.

All the while, the technology has gotten better. We have two promising new formats, SACD and DVD-A. SACD is a dangerous thing to get too excited about, as the technology its based on is still very poorly supported by pro-audio hardware manufacturers. DVD-A on the other hand, can be produced by just about any studio that’s already set up for DVD post work, or hi fidelity audio production. (There are a few adjustments and additions that need to be made).

But nobody is realistically going to care about wonderful surround formats, when they can just download the mp3’s that are universally compatible. So, this article, is about bridging that gap. It’s about bringing 5.1 mixes to the same wonderful world of open distribution as mp3s.

The Why

Why would we want to put our ac3 files up online? A lot of reasons actually, personally, since there is no formal standard yet for how to mix in surround, an increase in the available files, would make the pro-audio world a better place. More examples of music mixed in surround, can only help the audio community start to settle in on some of the more creative and effective techniques for using this medium.

Why AC3? File size mostly. Dolby’s technology most closely resembles mp3 for file compression, (and unfortunately fidelity loss) and compared with competing formats like DTS, this becomes a very important consideration for online music distribution. For a few rough numbers, consider this:

A seven minute song in 5.1, encoded at 44.1k would be about 12 megs, in AC3 format. Clearly larger than your average mp3, but not impossibly big. The same file encoded in DTS, would come in around 100 megs. Which makes it, just plain no fun to download.

The other difference is the availability of software decoders for listening to the music. Plain and simple, Dolby has been around the block. As a result, while it has its drawbacks, it is an ideal choice for online music distribution.

Why do it at all?

Surround sound sounds great when mixed correctly, and enough homes now have either computers with 5.1 setups or a home entertainment center that they use for their music listening and DVD watching. The bottom line, home entertainment is quickly becoming more integrated, and with the availability of low cost 5.1 systems in many peoples homes, its about time that we as engineers, producers, and artists begin utilizing those wonderful extra tools.


Surround in general has its benefits as well. From a Professional standpoint, having the ability to have 6 discrete channels makes for some very open creative options when it comes to mixing. We will cover in depth mixing techniques elsewhere, for brevity, I will only summarize here. First of all, the mere existence of a center channel solves a lot of problems that we have been compensating for in our stereo mixes for years. For the point of discourse, all sound that is centered in a stereo pan is supposedly creating an imaginary center channel. It is no leap of logic that having a real center speaker, means that the left and right channels no longer have to do this extra work of doubling ‘centered’ sounds, and can be freed for more spatially descriptive functions. Secondly, and probably most importantly of all, having a discrete LFE channel, allows the mixing engineer to give exactly the amount of depth to his/her mix that it needs, without worrying as much about the low end being lost altogether on cheaper speakers (Yes, there are cheap surround sets, but even they usually have a powered sub, if they don’t then they can’t listen to AC3 Dolby digital files anyway). Finally, having those extra rear speakers, while often abused, when used right can add just the right amount of extra ambiance to the mix, creating an absolutely immersive listening experience.

The how

Well, we’ve had some good news, surround sound is a wonderful happy format, and we can deliver it fresh to fans for less than 20M of bandwidth. Now for the bad news, this whole concept is useless unless you have some way to encode your mix into Dolby Digital AC3 format. If you already run a professional studio that is set up for this, then there is not problem. If you are a home studio enthusiast, you will have to find a solution that works.

You need something that will take your 6 channel discrete mix (L, R, Ls, Rs, C, LFE) into an encoded AC3 file. For a complete reference, Dolby labs keeps a list of licensed encoder manufacturers:

Once you have your AC3 file, your work is essentially done. You need to be able to listen to it though, and so do your fans and clients. To do this, you’ll need some sort of decoder and something to play it on.

If you have a Creative soundcard on your computer, you can use the included play center, however, if you’re like most computer users, you probably have winamp to play your mp3s. If you try to play an AC3 file in winamp, you’ll be lucky if you get no sound, otherwise the results could be horrific. But, we have a solution. Members of the open-source community have already seen and tackled this problem. (I will give you a walkthrough for windows machines)

The solution is simple and beautiful. Go to and make sure that you have the latest version of winamp. Once you have this installed, hoof it on over to:

and follow their link to the download section. Download the latest binary, and install it to your winamp directory (you can’t really mess this up, as they won’t allow an install unless the installer ‘sees’ winamp in the folder). Once you have it installed, open winamp and go to your options, and open the preferences dialogue  On the left side of the screen, click plugins: input. To the right you should see “Valex’s AC3 decoder for winamp…” click on that, and click on the “Configure” button that just became active.

Here you’ll find all of your juicy options. (The developers tell you about what each function does on their website, I’m only offering you a quick start, if you’re inclined, mess around with it, see what you come up with.)

Click on output: Set this to ‘winamp output’

Click on the drop down box below output. Set this to ‘3/2+SW 5.1 Channel’

You can adjust the output bitrate, but if your not comfortable messing around, you can leave it at 16 bit output.

Finally, open any windows folder. Click on tools and then folder options. Click on the tab labeled file types. Under this tab you should see a list of file types, find .ac3, and in the panel below click change next to ‘opens with’ if you don’t see winamp, select browse, and find winamp in your program files directory. That should be it. Winamp should now be your default Ac3 player.


What have we accomplished here? We’ve set up an online system for delivery of 5.1 audio files that are small in size, but big in their sound. We can now audition mixes for clients quickly and efficiently, and offer our fans a new way to listen to the experience. There are also ways to record these 5.1 ac3 files right onto a cd-r that can be played in just about any home DVD player. (I’ll cover this some other time).

In the meantime, keep mixing, practicing and experimenting. This field is wide open, hopefully it won’t be prematurely shut by tired old ears.

Thanks for reading.


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