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.
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.
Chris Connaker
Founder
Computer Audiophile
Comments
Posts: 106
Well that's
Well that's an interesting little tidbit they neglect to tell you, isn't it? Does the MacbookPro 17" have 3 USB ports? If so, not sure where the third one is located, but is it also shared with other devices? I like the smaller laptops myself and am leaning towards a MBPRo 15", but just curious. Besides, I like the Firewire to the hard drive idea anyway.
TheOtherTim
Posts: 3155
Yes the 17" does have a
Yes the 17" does have a third port on the opposite side.
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.
Chris Connaker
Founder
Computer Audiophile
Posts: 57
Well that explains it...
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...
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!
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!!!
Thanks for posting your findings Chris.
Posts: 359
.... the plot thickens
Chris,
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.
markr
Cannot find a MB ID, but the Model Identifier is: MacBookPro 3.1 and the Boot ROM ver. is: MBP31.0070.B00
Posts: 57
markr - Mine is the same model...
Plot thickens indeed!
Posts: 359
Hey Poo!
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.
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.
markr
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.
Posts: 359
I hate replying to myself, but it is necessary here
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.
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.
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.
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.
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.......
markr
(good morning, y'all!)
Posts: 57
Yeah I did the same update
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.
Posts: 108
Chris, This is actually true
Chris,
This is actually true of many models including some of the Apple products and PC products.
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.
Gang, they are all different also... my MacBook has 2 free ports and the hubs inside are not connected to the outside ports.
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.
I have a DELL laptop 15" unit here with 6 usb ports and only one of those works.
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.
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.
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.
Later,
Gordon
J. Gordon Rankin
~~~~~~~~~~
Wavelength Audio
Posts: 3155
As always, thanks for the
As always, thanks for the post Gordon.
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!
Chris Connaker
Founder
Computer Audiophile