Erratic sound cut-offs with rDAC (external DAC) on USB

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Erratic sound cut-offs with rDAC (external DAC) on USB

I use an external digital to analog converter named "Arcam rDAC" for playing my iTunes and DVD playback sounds from my Mac Mini to a High-End Amplifier in my living room. The DAC is connected to the USB port and installs itself as a external soundcard. If I'm playing - lets say music with iTunes - it erratically cut-off the sound playback from zero to tree times a day. The only solution to get the sound back is to unplug the USB cable and plug it in again.
I'm not sure if this is really a problem with my Mac mini or rather a software problem with OS 10.6.5.
Does anybody have an idea?
(By the way: All volume outputs are set to 100%, EQ, sound correction and so on in iTunes are off and Audio-MIDI-Setup is at 44100,0Hz/24Bit.)

Mac Mini, Mac OS X (10.6.5)

Posted on Dec 2, 2010 8:28 AM

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Answer 1

BSteely

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Dec 3, 2010 6:36 AM in response to m(at)x

What else is plugged into the USB bus? Any hubs in use?

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Answer 2

m(at)x Author

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Dec 4, 2010 4:50 AM in response to BSteely

Yes a HUB (passive, because also with the power plugged in the sound cut-offs are still happening) with external harddrives connected and an EyeTV-Stick.

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Answer 3

Dec 4, 2010 5:04 AM in response to m(at)x

You need a powered hub.

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Answer 4

m(at)x Author

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Dec 4, 2010 5:30 AM in response to DaddyPaycheck

The HUB is powered (but it doesn't make a difference if I use it powered or not, because the problem remains). But what does this matter anyway? The DAC is plugged in directly in the Mac Mini...

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Answer 5

Dec 4, 2010 7:29 AM in response to m(at)x

Try it without anything except the DAC and mouse attached and see if it works that way.

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Answer 6

BSteely

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Dec 4, 2010 7:36 AM in response to m(at)x

I would try an experiment where the DAC is the only thing plugged into USB, apart from maybe also the keyboard and mouse. See if the situation improves. If it does, then start reinserting the other devices one-by-one to see at what point trouble begins again.

USB uses a polling architecture which makes it less good for real time use as with video and audio and when compared with a bus architecture like Firewire.

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Answer 7

m(at)x Author

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Dec 4, 2010 8:06 AM in response to BSteely

Well, I will try to do that. But what if I want to view TV or a movie from the HD (WITH sound, of course)? That can not be the solution...
By the way: The sound may be off, but the DAC is still shown as output device unter System preferences > Audio > Output.

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Answer 8

BSteely

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Dec 4, 2010 9:38 AM in response to m(at)x

The mini has optical digital audio out. Can that be used instead?

If it turns out the problem is the USB bus is overloaded, can the HDDs be moved to the Firewire bus?

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Answer 9

m(at)x Author

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Dec 4, 2010 9:52 AM in response to BSteely

Unfortunately: "No" and "no". The Arcam rDac needs to be connected to the USB port due to its Jitter correction and the external HDDs are USB only... :o(

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Answer 10

BSteely

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Dec 4, 2010 10:06 AM in response to m(at)x

By the way: The sound may be off, but the DAC is still shown as output device unter System preferences > Audio > Output.

When the sound stops, does the rDAC still show up in the System Profiler as being attached to the USB bus? If the device is still on the bus, you should work with Arcam's tech support and see if they have updated firmware that can be installed. They may need a more robust routine to ensure the audio restarts in cases like yours.

If the Arcam is disappearing from the bus (System Profiler) altogether, that's a different kind of problem.

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Answer 11

m(at)x Author

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Dec 7, 2010 8:33 AM in response to BSteely

OK, tested the rDac alone on USB (nothing else connected to the USB ports) the past days: Problem remains. The rDac is still shown in the system profiler (under "USB"). What's irritating me, is the fact that the rDac is showing a red light at the USB input, indicating that there is no signal incoming!

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Answer 12

BSteely

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Dec 9, 2010 5:35 AM in response to m(at)x

OK, there's only a couple more things for you to try on your own before involving Arcam and Apple. First thing you can try is different USB ports on the mini. I'm not sure about your mini, but it has been true of past versions that not all USB ports are created equal. Some ports have been "native" ports driven directly by the HCI whereas others have been based on a hub, meaning a hub IC internal to the mini and soldered onto the motherboard. So the rDAC may work better from some ports than others.

The other things I would ask is, what length USB cable is in use? Is it a conventional length, like 1.8m or so? Or is it a long cable run? If the cable is inordinately long, you can try shortening it to see if that helps. If it does, then you are left to try and move the mini and rDAC closer together, or else perhaps use shorter sections of cable and then hubs in between to link the mini and the rDAC.

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Answer 13

m(at)x Author

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Dec 11, 2010 1:38 AM in response to BSteely

Hi BSteely, thank you for your patience and effort.
I definitely tried two of the four USB ports. (I think - but will verify it - tree of the for. If you look on the backside the first and second port from left and - as I think - the last one.)
Length and quality of the USB cable:
I tested/used three cables: 1) The one that was included with the DAC, 2) A high quality USB cable with gold plated plugs 1.8 meters and 3) By now a ultra high end USB cable ( http://viablue.de/com/kr2_silver_usb_cable_ab.shtml) of 1 meter. I think, its not necessary to test more on this side... ;o)
I just downloaded and installed the USB prober app from the Apple developers download section, but there are a bit to much information for me now... ;o)

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