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(asynchronous) USB DAC + external USB HDD = Problem?

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Hello, after being a passive member a long time it's time for my first post.. Sorry about the not-so-perfect english. :)



In a Norwegian hifi-forum it has been mentioned a possible problem regarding the use of an asynchronous USB DAC and an external USB HDD. I'm hoping someone here maybe has an answer/explanation..


Possible problem: When you use two usb-units (DAC+HDD), they are not synchronised according to the USB-standard. This means that the connection between the dac and computer is not reliable - even with an asynchronous USB DAC. When the asynchronous USB DAC sends a request for data to fill up it's buffer, it's not sure the computer is able to fulfil this request because the request is not synchronised whith the HDD USB-controller..


Is this a real problem or is it based on some kind of misunderstanding?


Is it any advantages of choosing a FireWire external HDD when used with a USB DAC?



Christian W.


iMac 21,5\"/iTunes/Pure Music -> Ayre QB-9 -> Pass Labs XP-10 -> Pass Labs X150.5 -> Avantgarde Acoustic Duo G2

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You should never use a USB hard drive with a USB DAC. The pure amount of synchronous data transfer over one link is too much for the computer to handle.


It is always best to keep the hard drive on say a Firewire link and the dac on the USB link for best results. Another idea which is even better is to use an eSATA II link from your computer to the external drives.





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Hi Christian - Thanks for posting your question. The problem I see is using a USB DAC with another USB device like a hard drive. Adaptive or Asynchronous USB is not really the issue. Many USB ports share the same USB bus inside the computer. This make the devices share the single resource (the bus). For example older MacBook Pro computers had a problem with USB DACs on a certain USB port because internally the keyboard used the same USB bus. Here is a link to an article about this http://www.computeraudiophile.com/content/USB-Port-Not-USB-Port


I highly recommend a firewire hard drive or using a USB port that you know is on a different USB bus inside the computer. On a Mac it's easier to see what USB buses are shared.


Founder of Audiophile Style | My Audio Systems

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Hi Gordon,


I am using an asynchronous USB DAC (Ayre) and I use a USB external HDD for my music files. I am not aware of any problem. The system seems quite stable. Can you please describe what problems you predict? How would I know if there was a problem?





Vista laptop


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  • 2 years later...

I have all my music (AIFF format) stored on an external USB HDD. I am looking to buy a USB DAC but obviously am reluctant because of this conflict.


My laptop only has USB 2.0 ports, therefore, would the issue be solved if I bought an expresscard34 to USB 3.0 and connected the external HDD to that? Then connecting my DAC to one of the onboard USB 2.0 ports.




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From the Ayre website (http://www.ayre.com/usb-adc-windows-vista7.htm):

"To ensure that the Ayre USB A/D converter is running on its own dedicated USB controller is largely a matter of trial-and-error. Normally the physical USB port will be connected to a "smart" controller that automatically changes from USB 1.1 (Full Speed) to USB 2.0 (High Speed or "Enhanced), depending on the requirements of the attached peripheral device. However, there will not be a dedicated controller for each port, so sometimes it may be a bit of a trick to find an arrangement whereby the Ayre USB D/A converter has its own dedicated USB controller.


To determine which USB devices are connected to which controllers, go to "Start - Control Panel - System and Security". Then go to "System - Device Manager". In the Menu, select "View - Devices by connection". You will see a "tree" type of display. You are only interested in the USB devices. Click on the symbols to expand the view of the "tree" and identify the devices that are connected. "


With only two ports, I would guess they are on the same controller, but you might as well check. I think your proposed solution with the expresscard should work fine. BTW, when I first got my USB DAC, I was using a USB HDD on a laptop with all USB ports on the same controller. I didn't have any issue with this arrangement and the music sounded fine. Now, whether the sonic quality was "optimal", that's a different question that I have not taken time to explore. I've since moved onto a PC with eSATA and my HDD is in an external case with an eSATA connection.


Having typed all that, I'm assuming you're using Windows ;o)




Roon ROCK (Roon 1.7; NUC7i3) > Ayre QB-9 Twenty > Ayre AX-5 Twenty > Thiel CS2.4SE (crossovers rebuilt with Clarity CSA and Multicap RTX caps, Mills MRA-12 resistors; ERSE and Jantzen coils; Cardas binding posts and hookup wire); Cardas and OEM power cables, interconnects, and speaker cables

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