Problems using optical out from Mac G5

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Joined: 03/02/2006

Hello everyone,

I'm trying to setup my system to utilize the digital outputs on the mac to our Alesis ADAT for digital-to-analog conversion, instead of using the mini-jack on the computer itself. However, for some reason, I am running into problems. Here is what I have done thus far.

Using the Alesis provided optical cable, I have taken the digital output from the mac into the digital input on the XT20 Adat. From there I have taken the analog outs from the Adat into my mixer. On the itself Adat, I have selected "digital input" 48K. I have also set the "input" on the Adat to "all" and monitoring to "auto." On the mac I have set the Audio Output to the Digital output 48k, 16bit in "audio-midi setup." In logic, the song is also set to 48k, and just to be safe, I re-launched core audio. However, I get no sound.

As a test, I switched the Adat to analog input and took the analogue out from the mac into the ADAT and everything worked fine. Thus the problem either lies in the Digital output from the G5 not working, the Digital input from the ADAT not working, or the Alesis XT20 is not capable of receiving on a digital input and converting it to analog output. I do not have another optical cable to test, so I'm hoping that this is not the problem, and instead I'm just missing something really simple.

Any ideas? Thanks in advance for any help.

We also have an old serial MOTU 2408 mkII audio interface that is currently not connect to our system. Is there anyway to use the digital/analog converters on this device without connecting it to a serial port?

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Joined: 02/12/2009

You've almost got it. The catch is that there are two flavors of optical. The ADAT speaks 8-channel ADAT optical. The Mac's optical output is only a two-channel optical format called S/PDIF. Here's the scoop on the Mac optical jacks:

http://docs.info.apple.com/article.html?artnum=86415

To further confuse matters, there are two ways to do S/PDIF. It can be sent via an optical cable or a coaxial cable (RCA jacks).

The 2408 only has S/PDIF on an RCA jack, not via optical. It also has ADAT optical. It will translate ADAT optical to S/PDIF on RCA. But I don't know if it can "see" the two-channel S/PDIF that the mac outputs. Try it.

Some devices which have ADAT optical will take S/PDIF optical and simply repeat it across all 8 tracks, so the L-R shows up on 1-2, 3-4, 5-6 and 7-8.

Try messing around with the 2408. It can be used as a stand-alone format converter.

Or, if your Mac has a PCI slot, install the PCI card that comes with the 2408 and you've got a major improvement! It can do 24 channels of ADAT I/O and has great converters for day-to-day stereo monitoring. (Hey, why didn't I say that in the foist place?)

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