• A USB Port is Not a USB Port



    This afternoon I was listening to a new DAC for review purposes. This DAC was connected via USB right next to a Benchmark DAC1 PRE. I was listening for a while on one DAC then switching to the other and back to the first etc... For some reason the sound was cutting out whenever I listened through the new DAC I was reviewing. I tried many things to solve the problem, but not the one thing that would have fixed it. I contacted the creator of this DAC and he soon reproduced the problem. He also told me how to solve the problem and that it was solely related to a design decision by Apple. Read more for the details that will effect every single USB DAC on the market.

    As you can see in the photo the MacBook Pro 17" and the MacBook 13" models have two USB ports side-by-side. I had a DAC plugged into each of the ports and the performance was vastly different. The DAC plugged into the front port sounded the same as it had the previous few months. But, the new DAC I am currently reviewing was plugged into the rear USB port. The sound coming from this DAC was cutting out at least two times per song. After trying several different remedies I contact the DAC's creator. I'll leave the name out for now because I don't want this DAC to be connected with this problem in any way. The DAC's creator told me what was happening. He suggested I connect my Benchmark DAC1 PRE to the rear USB port. When I did, the Benchmark was the one cutting out during songs. With the review DAC in the front USB port it performed just as it was designed.

    So, what is the deal? Apple's design of the USB architecture in MacBook/Pro models is flawed in my opinion. Apple routed the keyboard and mouse through the rear USB port/Bus (see photo). The keyboard and mouse are designed to go into sleep mode after short periods of nonuse. When activated again the keyboard and mouse draw too much power from the USB Bus and cause audio dropouts.

     



    click to enlarge
     

    Thus, the remedy is to avoid the rear USB port at all costs. On a somewhat related note is the use of USB ports for both external hard drives and DACs. As you can see USB ports are easily effected by devices connected to the same USB Bus. I highly recommend using a USB DAC with a FireWire drive or a network attached disk. This separates the DAC from other possible interference that is easily avoidable. We can't change the design of a MacBook but we can mitigate the problem by being smart about our computer connections.
    Comments 29 Comments
    1. The Computer Audiophile's Avatar
      The Computer Audiophile -
      Yes the 17" does have a third port on the opposite side.<br />
      <br />
      You bring up a good question about other devices sharing the other USB buses. Yes this does happen, but not in combination with the sleeping keyboard. These other devices do have a chance of causing problems though.
    1. Poo's Avatar
      Poo -
      Have had the 'audio drop out' problem you describe for quite some time now and it has been driving me insane. I have a 17" MBP which wirelessley access audio from a remote server, and I figured the dropouts were due to wireless. I have improved routers antenna, changed position (amongst many other odd changes) and the issue only solved itself recently...<br />
      <br />
      Once I upgraded to Leopard a few weeks ago (yes, slow off the mark I know...) the problem vanished. I presumed until now that the upgrade had mysteriously solved the problem, but after reading your explanation things are a little clearer. You see, I have had no reason to plug and unplug my DAC from the MBP - so it has always used the same USB port. The only time it has changed was during the Leopard install, when I moved the MBP to another room, and then back after install finished - plugging the DAC into the other USB port!<br />
      <br />
      This issue has been beyond annoying for me for over two months - nice to have it solved, but I'm not sure that it's any less annoying to know the reason!!!<br />
      <br />
      Thanks for posting your findings Chris.
    1. markr's Avatar
      markr -
      Chris,<br />
      <br />
      My 17" MBP ( C2D 2.4 GHz), purchased last October is probably the last mainboard rev. before the recent upgrade - maybe NOT. My USB arrangement looks somewhat different from the one you show. My screenshot shows 2 Axiom Keyboards and the M-Audio MIDI distribution box (the one that says 'vendor specific') plugged in to each of my 3 USB ports. Notice that there is an extra USB shown that isn't used (or useable). The keyboard and 'mouse' are all by themselves too. I don't have a port for that unused USB shown in the USB tree though - future expansion? . I don't experience any issues like those mentioned here (lucky again? - I hope...) , but I am experimenting now just to be sure.<br />
      <br />
      <center><br />
      <a href="http://www.computeraudiophile.com/files/markr-usb-bus-large.jpg"><img src="http://www.computeraudiophile.com/files/markr-usb-bus-small.jpg"></a><br />
      </center><center>click to enlarge</center><br />
      <br />
      markr<br />
      Cannot find a MB ID, but the Model Identifier is: MacBookPro 3.1 and the Boot ROM ver. is: MBP31.0070.B00
    1. Poo's Avatar
      Poo -
      Plot thickens indeed!
    1. markr's Avatar
      markr -
      For want of my screenshot being up on the site yet, does your USB Device Tree in system info show 7 total USB devices (Chris's screen shot shows 5 devices)? That is EVERYthing on that page. My USB structure is TOTALLY different from the one Chris shows. If yours looks the same as Chris's, then right now the only thing I can think of is something that most 'regular' Mac users probably haven't seen. <br />
      <br />
      I get upgrade notices for soft and firmware that are related to Apple "Pro" applications because I have some of those applications installed. Specifically, these are for Quicktime (!), Logic & Final Cut, but also for Aperture and a couple of others that I don't own. These upgrades explain that they are designed for the interoperability of these "Pro" applications. I could be jumping to software on this issue too quickly when it is actually a hardware thing at work, but right now I have a suspicion that this is what it is at the root of this. Especially given that Poo announced that his MBP is the same rev. as mine and he does have these issues. I hope that is the case, because then the fix wouldn't require hardware upgrades.<br />
      <br />
      markr<br />
      BTW: I haven't yet been able to duplicate the glitches that are mentioned here, and I've had no ongoing nagging sound issues as mentioned in this thread. BUT I don't have a second (non-PCI) DAC to add, and my A/D/A box is firewire.
    1. markr's Avatar
      markr -
      SO.... Having postulated about soft and firmware, naturally I checked 'Software Update' after posting the previous message. Guess what I found? Another "Pro" application interoperability and compatibility upgrade AND a Mac "EFI" upgrade to the Boot ROM version. <br />
      <br />
      <strong>aside: -- Did you know that newer Macs, and now some PC's don't have BIOS's (per se) anymore? The industry is moving to 'EFI': Extensible Firmware Interfaces instead.</strong> <br />
      <br />
      Poo, my Boot ROM version is now at: MBP31.0070.B07. This is the first of this type upgrade that I have had to do, requiring a shutdown, and then holding the power button down until I heard a beeeeeeep. The firmware was then upgraded in a way, visually, that I haven't yet seen.<br />
      <br />
      I checked system information afterward, and my USB devices still tally at 7, though they are slightly rearranged now. The Keyboard and 'mouse' are still separate from other devices however.<br />
      <br />
      Is all of this just synchronicity with regard to what this thread is about? I don't know, but I still think that soft/firmware is the issue here. ....gotta go and check to see what is going on with 'tha dang thing' NOW.......<br />
      <br />
      markr<br />
      (good morning, y'all!)
    1. Poo's Avatar
      Poo -
      Yeah I did the same update yesterday. Can't give you my ROM details ATM (am using PC and MBP isn't here now) but will reply when I can. Thanks for the added detail.
    1. Wavelength's Avatar
      Wavelength -
      Chris,<br />
      <br />
      This is actually true of many models including some of the Apple products and PC products.<br />
      <br />
      Really to blame here is Intel and their USB controllers. Some of them have built in hubs which can effect the way something works. Well maybe not Intel completely... all the VIA motherboards as well as almost any computer will have that problem.<br />
      <br />
      Gang, they are all different also... my MacBook has 2 free ports and the hubs inside are not connected to the outside ports.<br />
      <br />
      My HUSH pc is the worst. It has I think 8 USB 2.0 ports. But only 2 of them work at anything of high output.<br />
      <br />
      I have a DELL laptop 15" unit here with 6 usb ports and only one of those works.<br />
      <br />
      The point is check where you are plugged into. NEVER use a port on the front of a desktop computer. They are wired from the mother board and never work.<br />
      <br />
      For the PC you can download a copy of USBview and for the mac use the profiler or better yet the USB Prober. This will tell you the map of the ports.<br />
      <br />
      But Chris I must tell you I have never had a dropout on one of these ports. But I did have a customer with a new iMac which had the bluetooth keyboard and mouse and had connected a Crimson to the port that shared these and had a problem. I relocated the dac and there has not been a problem since then.<br />
      <br />
      Later,<br />
      Gordon
    1. The Computer Audiophile's Avatar
      The Computer Audiophile -
      As always, thanks for the post Gordon.<br />
      <br />
      Funny you mention your customer with the Bluetooth keyboard and mouse. I can reproduce the error 100% of the time with my Bluetooth keyboard and mouse!
    1. Codifus's Avatar
      Codifus -
      I find it somewhat bothersome for blame to be cast to all manners of USB when it comes to high quality digital audio transfer/reproduction.<br />
      <br />
      When USB was invented, I'm sure it's use an audio data transfer medium was not even envisioned. USB was basically invented as a convenient way to connect your keyboard, scanner and digital camera to your computer. <br />
      <br />
      Only recently did the audio universe catch on to the idea that they could use USB to transfer audio data from the computer to a DAC.<br />
      <br />
      Apple never intended for USB to be used for audio data, they wanted us to use firewire, and if we did, we would not be disappointed. High end production Music studios live on firewire based Digital audio applications.<br />
      <br />
      Sony and Philips invented S/PDIF.<br />
      <br />
      If we really are serious about audio, would we be using another medium, then?<br />
      <br />
      I'm not saying its wrong to use USB, just presenting the other point of view.<br />
      <br />
      CD
    1. Alan B's Avatar
      Alan B -
      Do the MAC mini USB ports have the same problem? Has anyone mapped the USB ports on the mini?
    1. The Computer Audiophile's Avatar
      The Computer Audiophile -
      This is something I've thought about quit a bit. I don't currently use a Mini so i can look at the configuration of the USB bus. Hopefully someone who does have a Mini will jump in. If not, you might want to post this in the forum where it will be more visible.
    1. cbarber's Avatar
      cbarber -
      I have a mac mini 2009 - what do I check for exactly?
    1. Alan B's Avatar
      Alan B -
      You want to be certain that your USB DAC is not plugged into the same USB Bus as your Apple Keyboard. To check your configuration:<br />
      <br />
      Select “About This Mac”, then the “More Info…” button. Then under the hardware tab you will see “USB”, select this and you should see where your DAC is connected.<br />
      <br />
      If it is under the Apple Keyboard, then try a different USB port.<br />
      <br />
      I have the previous Mac Mini and I had no problem finding a dedicated USB port. Hope this helps.<br />
      <br />
      Alan<br />
      <br />
    1. cbarber's Avatar
      cbarber -
      Thanks - here is how my USB tree looks in system profiler. The DAC is not yet connected. When I do connect it, after trying all USB ports, I could only get it to got to one of the two "USB Bus" trees, AND NOT into either of the "USB High-Speed Bus" trees. The first USB Buss tree has "IR Receiver" and the second has the Bluetooth Controller. <br />
      <br />
      Questions: <br />
      -If the goal is to get it into a part of the tree that doesn't have anything else in it, it seems that's not possible. Given that, do I want it near the "IR Receiver" or near "Bluetooth?"<br />
      -And the important question: Have folks with minis found this to affect sound quality?<br />
      <br />
      SYSTEM PROFILER>USB<br />
      <br />
      <strong>USB Bus</strong><br />
      --IR Receiver<br />
      <br />
      <strong>USB Bus</strong><br />
      --Generic USB Hub<br />
      -------Mouse<br />
      -------Keyboard<br />
      --BCM2045B2<br />
      -------Bluetooth Controller<br />
      <br />
      <strong>USB High-Speed Bus</strong><br />
      <br />
      <strong>USB High-Speed Bus</strong><br />
      <br />
      Best,<br />
      Chris
    1. Alan B's Avatar
      Alan B -
      Hi Chris:<br />
      <br />
      I have had my Mac mini since last July connected via USB to a Benchmark DAC1 USB and have never had not even one problem (as noted above). Mine also does not connect to the High-Speed Bus, but that has not been a problem either. I tried connecting my DAC to all 4 USB ports on the mini and not once did it mount in the tree with the mouse or keyboard. I believe the problem that started this thread affects some Macbooks (Pros) and not the Mac Mini.<br />
      <br />
      Have fun and enjoy your music server! I love mine.
    1. cbarber's Avatar
      cbarber -
      Thanks Alan,<br />
      <br />
      I wonder if the Mac mini 2009 is different.<br />
      <br />
      I've plugged the Cosecant into every port and it will only mount in the tree next to "IR Receiver" or "Bluetooth." They seem stuck there. So no matter what the Cosecant will be next to one of these.<br />
      <br />
      Anyone else with a 2009 mini experiencing this or have any idea why this is or if it makes a difference?<br />
      <br />
      Best,<br />
      Chris
    1. Alan B's Avatar
      Alan B -
      Chris<br />
      <br />
      Every time you plug the DAC into a different USB port are you asking the page to reload? I noticed on my Macbook Pro I have to do that or it just reads the same, just a thought.<br />
      <br />
      Alan<br />
      <br />
      <br />
    1. cbarber's Avatar
      cbarber -
      Yes, each time I close out of system profile and come back in to be sure.<br />
      <br />
      Thanks though<br />
      <br />
      Anyone else with a 2009 mini who can verify these results?<br />
      <br />
      Best,<br />
      Chris
    1. Solver's Avatar
      Solver -
      On my LG Xnote LM40 laptop USB ports are not working. As usual I connect Iriver player to the USB port and player is charging but not identified as storage device. Connecting other devices such as mouse or keyboard to the USB port won’t help <a href="http://ppcnation.com/">Search Engine Advertising</a>. I’ve performed a new installation of Windows XP and it also didn’t help. So my question is what’s wrong with my laptop and where should I look for solution of the problem? <br />