DIY Surround-Sound DVDs
Pages: 1, 2

Sidebar: Surround CDs

With Minnetonka SurCode CD-DTS ($99; Win) or Immersive Media Research Vortex Surround Encoder ($50; Win/Mac), you can create 5.1-channel DTS files you can burn onto CD-R and play in most DVD players. To your computer, the DTS file looks like a standard stereo WAV or AIFF with a CD-compatible sample rate of 44.1kHz. (DVDs typically use 48kHz.) But if you listen directly to the encoded file, you'll hear a sound somewhere between white noise and static. You need to run it through a DTS decoder to expand the sound back into six channels.

In a home theater setup, the decoder is typically in the receiver. The DVD player feeds the DTS signal to receiver through an optical cable, and the receiver in turn feeds six speakers through its six analog speaker outputs. A simpler, more compact option is to use powered multimedia speakers that come with a decoder box, such as the Logitech Z 5500s or Creative Labs GigaWorks series.

You can also burn AC3 WAVs and AIFFs onto CD, but the encoded signal sounds much harsher than the DTS one, so be sure to label the disc so no one tries to play it in a normal CD player.

Here are two sites with DTS and AC3 WAV files to download and experiment with, along with more background on burning surround-sound CDs:

Sidebar: The Multispeaker Mac

Mac OS 10.4 (Tiger) added a slick audio feature called USB audio aggregation. When you plug USB audio devices like speakers, mics, or audio interfaces into your Mac, you can address them as a single combined device. Using a stereo audio interface and a 4.1-channel multimedia speaker system I had lying around, here's how I used this feature to get true quadraphonic playback:

  1. First, I attached the USB audio interface, an Edirol UA-20, to the Mac, and plugged my two rear speakers into its left and right outputs.
  2. Opening the Audio MIDI Setup utility, I selected "Open Aggregate Device Editor" (Command-Shift-A) from the Audio menu and used the "+" button and checkboxes to define a device. (See Figure A.)
  3. After clicking "Done," I returned to the main window. I then selected my new aggregate device from the "Properties For" drop-down menu and clicked the Configure Speakers button. A sheet dropped down. (See Figure B.)
  4. Clicking the Multichannel button revealed a new drop-down menu with possible speaker configurations. I selected "Quadraphonic" and clicked the speaker-icon buttons to verify that a discrete signal was going to each. Clicking "Done," I was ready to rock in quad.
Fig. A: Aggregate Audio

Fig. A: After clicking the "+" button to define a new aggregate audio device, you use the checkboxes to enable inputs and outputs. I named my new four-in/four-out device "4x4 Internal + Edirol."

Fig B: Speaker Setup

Fig. B: Clicking the Multichannel button lets you configure multiple speakers. My choices were Stereo and Quadraphonic.

To test my new speaker setup, I recorded a quick musical demo with KAE Labs VocalWriter, a singing synthesizer with a built-in multitrack sequencer. I set track 1 to sing "One," track 2 to sing "Two," and so on, and then exported each track as a mono AIFF file. Opening a new file in QuickTime Pro, I inserted the AIFFs into four discrete tracks. (To insert files into discrete tracks, you open the source files one at a time in another QuickTime player, Select All, copy, and then add them to the new file with the command "Add to Selection and Scale.")

Then in the QuickTime Properties window (Figure C), I mapped each track to a different speaker. Here's the result, along with a quadraphonic movie of Mark Nelson's thunderstorm recording, so you can check it out yourself. If you don't have four speakers connected, the output should collapse to stereo.

Fig. C: Speaker Mapping in QuickTime

Fig. C: To map QuickTime audio tracks to specific speakers, press Command-J to open the Properties window, and then select the speaker you want from the pop-up menu.


David Battino is the audio editor for O’Reilly’s Digital Media site, the co-author of The Art of Digital Music, and on the steering committee for the Interactive Audio Special Interest Group (IASIG). He also writes, publishes, and performs Japanese kamishibai storycards.

Return to digitalmedia.oreilly.com.