Trouble in Promise-land

What's the first thing you do when you've got a display that has tons of interfaces and bandwidth at its disposal? Try them all at once to see if anything breaks of course. Over the course of the past few days that's exactly what I did. Unfortunately I did find a situation where things broke.

For whatever reason, if you're doing a lot of writes to the Promise Pegasus while playing music (or any other constant audio) through the Thunderbolt Display's internal speakers the audio will eventually corrupt. You can hear exactly what I'm talking about below:

TB Pegasus Audio Issue by AnandTech

This is a recording taken of me listening to music on the Thunderbolt Display (via its internal speakers) while writing a couple hundred gigabytes to the Pegasus R6. Note the introduction of what can only be described as really bad noise at the 6 second marker.

If you stop music playback and quickly resume, the problem will still be there. You have to restart the application that's using the audio codec to recover from this point. From a hardware standpoint, the codec just needs to go through an off/on (sleep/wake?) cycle to return back to normal. If you do this however and haven't stopped the transfer, the problem will creep up again. Stopping the transfer while playing back music won't fix the issue either. You have to stop the transfer and restart the music playback application for it to go away.

The issue goes deeper than that. I went out and bought a Creative Labs X-Fi Go Pro USB sound card to see if the problem stopped at the internal audio codec or extended to all USB sound devices. Unfortunately, it does even happen if you're using an external USB sound card connected to the Thunderbolt Display. Connect the same sound card directly to your Mac or use your Mac's 1/8" stereo jack and the problem goes away.

I was worried that what may appear as noise through speakers could result in data corruption over USB transfers. I ran the Pegasus write test while copying a bunch of files to an SSD attached via USB to the Thunderbolt Display and never saw any corruption on the SSD. This appears to be limited entirely to audio playback.

What's truly bizarre is I can only get the issue to appear when writing to the Pegasus, hundreds of GBs of sequential reads don't seem to produce it. Short bursts of writes don't seem to cause it either. Sending tons of data across the monitor's Gigabit Ethernet, FireWire 800 and USB ports doesn't seem to trigger it either. It appears to be an issue with the Pegasus and the Thunderbolt Display. But which device is ultimately at fault? Is it a problem with the Thunderbolt Display or the Pegasus? Ideally I'd use another Thunderbolt storage device to see if the issue remained, but I couldn't get my hands on a LaCie Little Big Disk.

I thought of something else.

First I needed to test and see if perhaps the issue was related to ultra high speed transfers. As we've already shown, the Pegasus can push as much as 1GB/s over Thunderbolt whereas none of the other bandwidth eaters come even remotely close to that. To determine if the issue was data rate invariant I wrote to the Pegasus at different speeds ranging from 480Mbps all the way up to 7.2Gbps. I tried putting SSDs in the Pegasus as well as standard mechanical hard drives. The problem remained. I got audio corruption regardless of what drives were in the Pegasus or what speed I wrote to the drives. The problem wasn't related to transfer rates.

I also took apart the Thunderbolt Display to confirm there weren't any obvious issues on the controller board (E.g. putting the Thunderbolt IC far too close to the audio controller). Nothing obvious there either.

While I was doing all of this, Apple put forth a Thunderbolt firmware update the other day, however it didn't seem to address the issue either. So I went back to my testing.

Since the problem appeared regardless of how fast (or slow) I was transferring and all I needed was another Thunderbolt storage device to vindicate either the Pegasus or the Thunderbolt Display I turned to the trusty MacBook Air.

As I mentioned in our original Pegasus review, if you have two Thunderbolt equipped Macs and a Thunderbolt cable you can actually put one of the machines in target disk mode and access its drives via Thunderbolt on the remaining Mac. You don't get super high performance but you can get around 500Mbps. Since I had reproduced the audio corruption issue at an even slower data rate I decided to give this a try.

I booted the MacBook Air in target disk mode by holding down the 't' key after turning on the machine. My MacBook Pro was connected to the Apple Thunderbolt Display and a Thunderbolt cable connected the display to the MacBook Air. This was the same setup as the Pegasus, but with the MBA in place of the Pegasus.

I wrote to the MBA just like I did the Pegasus (from a file server connected over the Thunderbolt Display's GigE, transfer rates were capped at around 500Mbps from the file server). After a couple hundred gigabytes were transferred without any audio corruption I swapped out the MBA and connected the Pegasus. I copied the same files at the same rate from the same source. After no more than 7GBs were written to the Pegasus the audio stream started to corrupt.

Based on my testing I can only conclude that the Pegasus seems to be at fault here, not the Thunderbolt Display. Given that the Pegasus was introduced prior to Apple's Thunderbolt Display it's not all that surprising that this issue made it through to production. It's unclear what the root cause is but it's hopefully something Promise can address either through firmware or a driver revision.

Update: I'm still verifying that this is indeed a "fix" but it looks like if you use a USB sound card plugged into a USB hub which is then plugged into the Thunderbolt Display then the sound corruption doesn't happen. This seems to point at noisy power as being the cause with the USB hub acting as a crude filter. It's still not ideal but this may be a workaround for Pegasus users until Promise supplies a fix.

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  • A5 - Friday, September 23, 2011 - link

    No shit. Every single review, everywhere, where the hardware is provided by the manufacturer is advertising of some form. This is why you rarely see truly negative reviews of anything. Reply
  • ltcommanderdata - Friday, September 23, 2011 - link

    And what monitors are you looking at to get those prices?

    http://store.apple.com/us/product/MC914?mco=MjQ1Mz...

    The Thunderbolt Display is $999 not $1200.

    Dell's most comparable device is the U2711 which is IPS and is $1099 regular price, although it's currently on sale for $719.

    http://accessories.dell.com/sna/products/Monitors_...

    I don't know how frequently Dell does sales, but at regular price the Thunderbolt Display is in fact cheaper than Dell's while including more dock features like ethernet, firewire, speakers, etc.
    Reply
  • Stas - Friday, September 23, 2011 - link

    Do a google search on the model and you will find at least 5 online sellers that have the Dell monitor for <$850 Reply
  • Constructor - Friday, September 23, 2011 - link

    Sure. The Dell doesn't have an LED backlight, however, so apparently they're selling off the old stock with CCFL backlights before moving on to LED as well.

    It's tougher to get a larger colour space with a (white) LED backlight, but on the other hand it's mercury-free, uses significantly less power and lives longer than CCFL.
    Reply
  • doubledeej - Sunday, September 25, 2011 - link

    CCFL backlit monitors still have a better image. That's why you find them on the high-end monitors from other manufacturers. Apple is sacrificing quality by moving to LED. Look at the charts in the article. The Thunderbolt and Cinema Display monitors both fall in the bottom third of nearly all of them. They aren't that great. LED gives better power usage, but it comes at a price in terms of image quality. Reply
  • Constructor - Sunday, September 25, 2011 - link

    Better power efficiency, better longevity, zero mercury.

    Quite significant advantages.

    And in most metrics the TBD is actually pretty decent, particularly for its resolution and price.

    CCFL makes it cheaper to get a larger colour space than with RGB LEDs again at the very top.

    But for that it's far dirtier in all three dimensions (wastes power, turns the display into e-waste a lot sooner and releases mercury if not dismantled very, very carefully – and even then the mercury remains hazardous waste).

    Very few people actually have a use for an expanded colour space. Still few people actually experience limitations with brightness uniformity (my iMac 27" is fully sufficient for all my uses, with no problem noticeable). And all people benefit from the advantages.

    It would have been silly for Apple to make a display that's specialized to only very few people's needs and saddling everyone with lots of disadvantages. Eizo can do that. They've got many models and they are largely specializing on these kinds of uses (and even they are on their way towards LED backlights).
    Reply
  • jecs - Friday, September 23, 2011 - link

    He went to the Apple store and confused the starting iMac to the Thunderbolt display. Some are so eager trying to look calm and cool but forget to check the facts.

    And you started saying "Nice but..."
    Nice to what? if you did not check the real price you are objecting
    Are you going to say now that you like the Apple display?
    Reply
  • TypeS - Friday, September 23, 2011 - link

    Better check the price again there bud, it's $990.00USD

    http://store.apple.com/us/product/MC914LL/A?fnode=...

    The Macbook Air also starts at $990.00USD as well:

    http://store.apple.com/us/browse/home/shop_mac/fam...

    That's a grand total of $1980 before taxes

    The 13" Pros starts at $1199 as well.

    Dell lists it's U2711 at $1099 retail, with a current sale price of $949.

    If we take your assumption that ASUS/Samsung have similar spec'd and functional alternatives or $900, the total savings is $150.That is a far cry from half.

    Anti-apple critics are just as bad as the brainwashed Apple fanboys when they start pulling facts out of thin air.
    Reply
  • cactusdog - Saturday, September 24, 2011 - link

    The prices I quoted are from the Apple website in my country and they are accurate. Apple charge us a lot more than they do in the US.

    You're choosing the cheapest/smallest macbook that nobody wants and saying they are cheap. They are not. You can get a similar speced notebook for much less from Asus.
    Reply
  • mcnabney - Friday, September 23, 2011 - link

    Didn't you read the review? This display has poor color accuracy so you really can't compare it to displays that have it. Anand indicated that people accustom to laptop displays wouldn't notice it, but I guarantee that people who have historically bought and needed high quality displays WILL notice it. So you can't really compare Apple's new display to competitors that make displays for the publishing/imaging business. Reply

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