[Filmo]

Just got the Transit USB interface because in theory it allows you to pass Dolby Digital and DTS signal to a surround capable receiver.

I've installed the latest driver (1.6) on a 10.3.9 1.25ghz 1gig RAM macMini and played around with all the system panels but I seem to only be able to get PCM digital stereo audio out of the system, not Dobly Digital or DTS

Normally, when my surround system gets a Dobly Digital or DTS signal from a TosLink optiacl feed, the "Dolby Digital" or "DTS" light on the front of my reciever lights up and acknowledges that it is receiving a surround feed. (I've tested the input with a DVD player feeding optical DTS and DD signal on the same cable, so I know it's not a receiver or cable issue)

When I feed the optical signal from the Transit to the receiver, only the "PCM" light goes on and it indicates a "Left-Right" feed, not "Dobly Digital" and a 5.1 feed.

In the system panel for Transit USB it indicates a pull down for the AC-3 output and changing it amongst the variuos options does nothing to affect the signal the surround receiver is getting.

I've looked in Apples DVD Player and even tried the VLS media player, but still don't get a DTS or DD pass-through??

What am I doing wrong?

(The Transit USB is advertized as being a way to get 5.1 sound out of a macMini. Also their manual sucks, and doesn't talk about this at all.)

[jamil5454]

I've got the Transit USB working great in 5.1 mode on my iBook. I've got the Creative DDTS100 decoder though, so maybe your decoder isn't recognizing the dolby signal from the mac mini.

[Filmo]

So I figured it out. Transit installs a seperate utility called "Audio MIDI Setup" which needs to be set to "Encoded Digital" ouput instead of 2 ch. 16bit. Once that's set, in the Preferences of DVD player, you can then go to Disc Setup and set Audio Output to "Digital Out - M-Audio".

In the System Panel, select M-Audio Transit USB and set active Channels to "Output AC-3"

Once done, I now get 5.1 passed-through to my receiver and the receiver properly decodes the signal as a DD 5.1 or DTS stream.

(Why the System Panel can't handle all the settings is beyond me instead of requiring setting both the Panel and a seperate Audio MIDI program.)

I found this page particularly helpful in solving the problem:
http://techdir.rutgers.edu/osx-audio.html

[Filmo]

Now that I've got it working here are a few observations:

1) Final Cut Pro - when playing video on the time line with the Transit USB device selected as the audio output source, the picture and audio are not in sync. I've set the latency to the lowest possible setting, but there still appears to be some latency issue that shows up as sync problems. I'm using a USB 2 hard drive, so perhaps there is an issue with using the USB bus for both the hard drive and for driving the Transit USB device.

2) 5.1 and DTS sound just like they should on movies when you adjust the Transit System Panel to output AC-3. (be sure to set 'pass through' in the AudioMidi setup program as discussed above.

3) iTunes require that you switch back to straight PCM digital output in the control panel in order to get sound.

Unfortunately, it appears that the driver can not 'auto-detect' AC-3 versus straight PCM, so you have to manually switch back and forth when using DVD Player and iTunes. Not a big hassle, but definitely a small annoyance.