|Comments on 5.1 Audio, Game 3D Audio and OpenAL on the Mac:|
Last Updated: 3/13/2002 6 PM
|(Updated with reader comments.)|
After reading the recent reader review of the Midiman Audiophile 2496 vs Mac SoundBlaster Live cards, a reader asked about 5.1 audio support on the Mac. I wrote Brian Souder of Creative Labs who sent a reply with his comments on 5.1 audio, 3d gaming audio and OpenAL for the Mac.
(Brian's email reply follows.)
To get right to it, AC3 (Dolby) surround sound and game 3D audio are
commonly confused. Even our PC customers think they are the same
thing. AC3 or movie surround sound (there are other formats too, but
let's keep it simple), is audio that has been encoded on a disc that
needs a decoding device like a 5.1 Live/Audigy to decode, or a set of
speakers that has a decoder built in to play back. Game 3D audio is
generated by a set of mathematical equations in real time to make an
event happen from a certain direction. (OpenAL and EAX 3.0 <PC>) are
examples of 3D API's that will position audio) I guess you could say
they are the same but different. What it really comes down to is the
source and the output. On the PC, we use the digital out (2 pin digital
on DVD-ROM) to pass the digital audio to the sound card. This includes
the AC3 signal if the DVD-ROM driver allows for the signal to be
transmitted. On the Macintosh platform, Apple sends the AC3 signal down
the IDE cable. I think we ran into problems when we experimented with
picking up the AC3 signal from the system board, If I am correct, we
had duplicate audio (analog & digital), and the digital was out of
sync. This was on OS 9, so sound manager's 2 channel setup may have had
something to do with this. I'm not sure if OS X handles this better or
not. From what I have been able to find from Apple's documentation
(which is very little), they say they can do 5.1 audio. I think they
have plans of doing USB or 1394 based speakers for this someday (this is
a guess) because they discourage vendors from making PCI devices. I
read through the Audiophile 2496 manual, and I'm not convinced they have
AC3 from DVD working. They keep referring to your audio application
sending them the AC3 signal that can be passed to a set of decoder based
speakers (no on card decoding either). If I am right, we are in the
same boat here. The Creative OS 9 drivers will pass a digital signal
through from your AC3 based software. (In other words send me a signal
and I'll pass it) As far as phase 2 of your reader's question, the Live
is the only card that is capable of game 3D audio. The Audiphile would
need to have the OpenAL call re-encoded on the fly to AC3 to be able to
do the same thing we do with 4.1 and 5.1 analog speakers. It didn't
appear the Audiophile 2496 had front & rear audio outputs. (Correct me
if I am wrong)
The Sound Blaster LIVE and the Audiophile cards cross paths at certain
spots. I am sure that they make an excellent product, and I certainly
would not diminish their accomplishments. In fact, from what I have
seen in the OS X development documentation, it is a real achievement to
have drivers already. It looks like they do a good job handling audio
I/O and MIDI. It also sounds like we are both plagued by Sound Manager
interference where the lagging and bogging come in. The point I brought
up about the AC3 wasn't to detract from their product, but to clarify
what you are actually getting. I think getting DVD AC3 from current
systems is going to be a challenge. At this point, the cards diverge
paths. The sound blaster is targeted at the gamer and low end
musician. The audiophile is targeted at the semi-pro musician.
Is there are card that does AC3/Dolby surround sound playback of DVD
movies on my Macintosh - the answer should be NO. (I'm Pretty Sure)
Maybe someone would like to call their support group.
Is there a card that will do 3D game audio - Yes - the Sound Blaster
LIVE for the Macintosh does 3D games audio. Unfortunately, it only has
OS 9.x drivers currently, even though there are more games coming out
for OS X. Are there a lot of titles - No. The game makers are very
excited about the prospects, but the OpenAL spec is on the young side. I
have seen comments about it needing to be updated. OpenAL is still
under constant development. It currently has carbon compatibility.
Will we see more OpenAL games? I think the game makers are going to
wait to see what happens to the market, but I would guess it would be a
relatively simple patch to add OpenAL back in. We shall see.
Thanks For Writing,
Two readers replied to Brian's comments noting similar comments about AC3 audio via IDE cable on the PC. Here's one of the mails with the most detailed comments:
I am regular contributor on the AVSforums specially when referring to the Mac as a home theater system. I had to buy a dedicated PC to be my DVD player because of the lack of 5.1 sound and customizable display resolution and timings in the Mac. So I agree with Brian Souder with respect to the dismal state of the Mac as a home theater computer. However, in the Ti and iBooks I beleive the Mac far outshines PCs as a portable DVD solution.
However, this letter is to clarify a point of Bryan's. To obtain AC3 (multichannel) audio output on a PC the majority of home theater enthusiasts use s/pdif pass-through. This means that the digitally encoded multi-channel sound from a DVD is delivered to an external decoder. Most audio receivers will accept s/pdif input and decode and amplify to speakers multichannel sound (Dolby Digital or DTS). In the PC this is achieved through the IDE cable also. Not through the digital 2-pin out of the DVD-ROM as Bryan states.
In the AVSforums many people have experimented with the 2-pin output on DVD drives and as far as we can tell you can only get 2-channel PCM.
Hopefully Apple or a third party solution will come about and will let me use my silent Cube as my DVD player.
FYI: none of the USB devices that can extract digital sound from the Mac (and only one on the PC, not the extigy) will allow s/pdif output and multichannel sound.
Another reader wrote commenting on the Wired4DVD PCI card
Just a quick counter-point on an issue Brian Souder brought up...
Quoted from Brian Souder of Creative Labs:
"Is there are card that does AC3/Dolby surround sound playback of DVD movies
on my Macintosh - the answer should be NO. (I'm Pretty Sure) Maybe someone
would like to call their support group."
This is not true. Although the card is now discontinued because it lacks OS
X drivers. The Wired4DVD PCI DVD decoder card successfully passed AC3/Dolby
surround sound to an external surround sound decoder and system.
Brian says this can't be done with the SoundBlaster because Apple passes the
AC3 audio over the IDE cable yet the Wired4DVD card manages just fine with
no extra connections on the card other than plugging it into the PCI slot.
I wrote an email way back when the SoundBlaster came out to Creative asking
if they would have AC3 audio-out on their cards and they said it flat out
"can not be done" because Apple was passing the AC3 signal over the IDE
cable. I replied with a polite yet to the point email saying that the
Wired4DVD card that was sitting in my G3 at the time (now G4) manages to do
this just fine...I guess its no surprise I never heard any sort of reply to
- Jeff Nelson
The Wired4DVD card has no OS X drivers. I reviewed it here 2 years ago, but didn't have a decoder to test the AC3 audio out.
Other Audio Related Articles: See the links at the bottom of the current Audio Column at www.xlr8yourmac.com/audio.
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