Thanks to clever data compression, it's possible to pack six channels of audio into a stereo WAV file. Played back normally, this file sounds like static. But play it through a DTS or Dolby Digital decoder into a 5.1 speaker setup, and the static expands back to six-channel surround. (This Swedish radio site has a bunch of free surround WAVs to explore.)
You can even burn the encoded WAV file to an audio CD and play it back in most DVD players. But configuring a computer to play these files is not so obvious. First, you'll need a digital audio output; my Mac has a built-in S/PDIF optical output, so I was set. I just connected that to my decoder/speaker setup with a single optical cable.
The unintuitive part is that changing the volume on the Mac collapses the signal back to static. To hear it as Dolby (and DTS) intended, you need to keep the software volume control at 100%. If you use iTunes to play back the files, you also need to disable all other signal processing: EQ, crossfading, Sound Enhancer, Sound Check, and any level adjustment you've made to the sound file in its Info window.
This Apple technote shows all the settings. It doesn't mention the Windows version of iTunes or using external audio interfaces, but I was able to play DTS and DD WAV files from Windows iTunes via an Apple AirPort Express. Pretty cool — wireless surround music!
For more surround shenanigans, see my article “DIY Surround-Sound DVDs.” It includes links to more free surround WAVs plus inexpensive software you can use to make your own.
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@Anon: Can I maintain a true digital path (with no D/A/D conversion) playing from iTunes [via S/PDIF]?
Well, there'd be no D/A/D conversion, because all the audio is shuttling around inside software, but that's not to say there wouldn't be digital processing. We'd need an Apple software architect to weigh in here, or a way to scope the bits coming out.
However, I've tried a number of S/PDIF interfaces on my Mac and PC, and the only ones that pass an uncorrupted DTS signal have been the built-in optical output on my G5 tower and the AirPort Express. So it's likely you'll get good fidelity using the built-in hardware on your system.
My question is a bit more basic - on Mac with an optical output, can I maintain a true digital path (with no D/A/D conversion) playing from iTunes, assuming:
volume is at 100&
Eq is OFF
Cross Fader is OFF
Sound Enhance is OFF
I have a high quality pre-amp/processor, and I'm ripping my (stereo) CD collection as Apple Lossless - I'd like to maintain a pure digital path until the point the signal reaches the processor.
Alternatively, what does AirTunes do when streaming lossless? Does it do a D/A/D conversion before streaming, or will it maintain the digital signal if I obey the above iTunes restrictions?
Thanks
@Philip: DTS CDs should show up in iTunes just like normal CDs. But they'll sound like static if you play them back directly. Playing them through the setup you've described — AirPort Express into a hardware DTS decoder and surround speakers — has worked for me. I've even been able to rip DTS files from a CD as AIFFs or WAVs and play them back.
As I noted, though, you need to make sure iTunes isn't altering the signal: volume must be 100%, EQ and SoundCheck must be disabled, etc.
i just found a cd with dts sound the extension of the files is *.dts can i play them with my itunes player on my imac through my apple express which is connected via an optical cable to an amplifires with dts ???
i try just to play them on itunes but it won't even put it on the playlist. any changes i have to make ??
thanx
The new iTunes 8 is now screen reader friendly on both Mac and PC, or use your screen reader to purchase or download content from the iTunes Store.
@Dave:
is there a way to get surround, or virtual surround, from 2 channel sources (like old mp3s)?
The easiest way to get virtual surround from a two-channel source is to run the signal through a processor like the Creative Labs X-Fi 5.1. (I'm not sure if this particular device works with Macs.) Many consumer receivers also have an "upmix" function to spread out the sound — or simply route the stereo file to both the front and back speakers. My Logitechs can do that.
I'm not aware of any consumer boxes or programs that convert stereo audio to Dolby Digital or DTS on the fly, though.
Another time-honored trick is to run the red wires from your amp to a third (or third and fourth) speaker situated behind you, causing it to output the difference signal from the right and left channels. This is the so-called Hafler Difference Circuit popularized by Brian Eno in the liner notes for Ambient 4.
Thanks David - super helpful.
First, your source must be encoded in DTS or Dolby Digital (AC-3)
So, is there a way to get surround, or virtual surround, from 2 channel sources (like old mp3s)? My speakers have onboard dolby pro logic 2, so maybe that would do it anyhow? i also got the griffin firewave, though it seems redundant since the speakers have onboard chips. maybe i'm assuming this is more complicated than it really is...
@Dave:
Will my macbook automatically output surround sound when I connect using a toslink cable?
No. First, your source must be encoded in DTS or Dolby Digital (AC-3). Then you need to make the software adjustments I mentioned above and in the comments. In DVD Player, select Digital Output. In iTunes, turn off all processing and set the volume to 100. You can even play DTS and Dolby files in the Finder's Get Info window if the volume on the QuickTime controller bar is set to maximum.
@David 8/9 5:58 "I bought a set of Logitech Z5500 powered computer speakers..."
I just was given a set of Logitech Z680 speakers, which is almost the same as the Z5500 (precursor I believe). It is a 5.1 surround system with onboard dolby processors and digital input. Will my macbook automatically output surround sound when I connect using a toslink cable, or will i need an external firewire card like the soundwave to get "upchannelled" surround sound from stereo sources like old mp3s?
I guess the general question I have about mac audio is: when connected using a digital cable, will os x applications like itunes automatically output surround sound?
Thanks for any answers to what might seem like a naive question...
@Noah2:
Is it possible to use Apple's DVD Player with a multi-channel Firewire audio interface to play DTS files off a CD? What's DTS stand for?
Hmm. You'd need to decode the DTS in software, which I don't think Apple DVD Player does. You might be able to use a combination of VLC and Soundflower to do that, though.
DTS = Digital Theater Systems
@Noah: Can you recommend a DTS/Dolby decoder?
If you already have speakers, you might look at a consumer surround receiver with optical input and six analog outputs. Audio writer Don Lindich spotted this refurbished Onkyo for $119.
I bought a set of Logitech Z5500 powered computer speakers, which included a small decoder box with an informative display. With shipping, these systems run about $250-300. That was mostly to mess around with; for a more serious system, you'd want full-range speakers.
Is it possible to use Apple's DVD Player with a multi-channel Firewire audio interface to play DTS files off a CD? What's DTS stand for?
Can you recommend a DTS/Dolby decoder? Amazon.com sells one called the Midiland ADS 4000 Dolby Digital/DTS Decoder for $199, but that's more than I wanted to spend.
@Terry: Good point. Another point of confusion comes when using Apple's DVD Player. To get it to pass surround sound, you need to burrow into the preferences and select Digital Output.
I don't understand why Apple doesn't include a single surround sound preference that, when selected, would automatically set and grey-out all the preferences discussed in the Apple TechNote. It's great the capability exists, I'm just not sure a few months from now when I'm doing something in iTunes I can remember every preference I need to stay away from once this has been set up.
Apple, please include a Surround Sound preference in iTunes!