Windows 7 x64 USB Audio Clicks and Pops with Musical Fidelity M1A DAC

(and also stuttering and freezing issues with the Musical Fidelity VLink 192 DDC)

Background/Problem

Normally, I do not write about PC problems into which I've run and their solutions, but this particular saga was extremely perplexing, and occupy the better of 50+ FTE hrs over 7+ calendar weeks of my testing, and somewhere around $250 in various test components and finally an additional $425 splurge on a DDC (a big investment for a $725 DAC, but I do love the sound of the Musical Fidelity M1A DAC!). I am hoping this information may help save some other poor soul experiencing similar issues a lot of sweat and tears.

The Quest for a Solution

• Is the hub the issue? Tried various mother board ports. Things got worse! Pops within minutes.
• Could a powered hub actually help? (There was a post on an M-Audio forum suggesting as much.) Well, I tried a bunch of hubs, both powered and unpowered, including Amazon, C2G, 2 Belkins, and a Pluggable. Only the older Belkin 4 port helped -- yes it was powered, but it actually helped equally without the optional power plug! Its performance matched the hub built into my LCD (maybe once every hour).
• What's all this talk about DPC Latency? I am sure that for some people, this may indeed be the root cause. But my PC is pretty beefy, even for today. And it is barely loaded. DPC Latency checker showed no issues.
• How about a dedicated USB PCIe card? I've tried two, both Western Digital USB 3.0 and a StarTech USB 3.0 cards. The latter because it takes supplemental power via an eSATA power connector. There were other posts on the Web suggesting a power shortage issue. No difference.
• So I am one for two on PCs. How about yet another PC? Borrowed an old HP laptop. Well, guess what? Won't even connect to the DAC consistently on all ports. Turns out that my Belkin 10' cable is flaky. Actually, I tried a bunch of USB cables -- the shorter ones connect fine, but the longer ones all had various issues with the HP laptop. Ah ha, I thought. I need a better cable! I don't buy into fancy audio USB cables as a good DAC (or a good DDC) should be the piece to handle the jitter issues (more on this later) and beyond that, digital is digital. But could a cable be causing so much loss that it is generating the pops? Well, I got myself a Pangea 3m cable (I need the length). Now all ports on the HP laptop work fine. But still the pops -- on both the HP PC and HP laptop. What is it about HPs? (More on this later)
• With a mitigating hub in place, there was exaggerated popping when there's a power line disturbance (fridge compressor turning on, for example). So is bad power somehow to blame? Well, after trying (and returning -- boy, return shipping is pricey on heavy stuff) an automatic voltage regulator, I concluded it made no difference. Also tried putting various pieces on same and then on separate circuits (both same and separate phases as well). I did not try an online UPS -- those things are > 45 dB in noise which is too high for a living environment.
• Related power thought -- Is it power management on the PC? Several posts suggests that power management (either CPU throttling, or USB selective suspend, or PCI link state power management for my USB card, which I decided is a better path as it is a dedicated card for USB audio use)? I've tried various combinations -- no difference.
• NIC drivers... a lot of posts suggests upgrading, esp if you have the Realtek chip set. Well, I do. But, no difference.
• Is it the opposite type of power management? Avid suggests that their product has trouble with USB audio clicks and pops on HPs and Dells due to Intel Turbo Boost increasing the CPU speed. Well, unfortunately, my BIOS did not have a setting to disable it, but I did try running with CPU power management set to max of 99%, which effectively disables turbo boost. (Gee -- turbo boost reminds me of the 80s with a turbo button on the front of PCs!). No difference. But in the process, I did discover Intel Turbo Boost Technology Monitor and CPU-Z, both of which will tell you what the current CPU throttle s is.
• OK, desperation is now setting in. I decided to go nuclear. Let me stick a DDC into the picture. It seems like all respectable 192kHz DDCs use a driver developed by Thesycon with the XMOS chip. Sure, it's a pricey investment, but worth a try. And I do intend to eventually get my hands on 192 kHz files. So I picked up a Musical Fidelity VLink 192 along with an AudioQuest coax 75 ohm cable. Two surprises:
  1. The sound quality actually improved, even for files at or below 96kHz sampling rate! I suspect this is the jitter discussion -- the VLink 192 must be better at jitter and is passing a better quality digital signal onto the M1A DAC. So this justifies the DDC though now my overall budget for the DAC project has been bumped close to the mid-range for DACs.
  2. The Galvanic isolation helps! One thing I noticed when tryig the various hubs is that some hubs would result in some ground loop hum. If the hubs go through the VLink 192, no hum.
  3. The clicks and pops are gone, but no nirvana. Now, every 1-2 days, the audio would get into a stuttering state where only a reset of the VLink 192 will fix it. The stuttering is constant with each sound that plays. (So not just a one time slowness issue.) This seems to happen only when the PC is idle (i.e. screen saver kicks in) and quiet (i.e. if I keep music playing, the issue does not occur.) Moreover, after 3-5 days, the PC would freeze, requiring reboot!
  4. More details in the Solution discussion below, but further digging revealed a potential problem with nVidia's PowerMizer that slows down the clock speed when the GPU is not in use. This turned out to mitigate most (but not 100%) of the pops using the M1A DAC by itself (w/o the VLink 192)!

Update: August 6, 2013

And the Solution is....

1. Quashing nVidia power management (by setting it to prefer maximum performance in the nVidia control panel) can eliminate most, but not all, pops. This may be good enough for many.
2. But if you demand perfection, the VLink 192 is pop free - but it has a potential stutter issue when the PC is idle
3. Resetting the default audio device can fix the VLink 192 stutter (and this can be automated via Task Scheduler)

The root correlation turned out to be nVidia's power management mode. Search for "nVidia PowerMizer interrupts" and you will find many posts talking about how power mode changes in nVidia can cause a flood of interrupts leading to audio pops! (Unfortunately, if you don't know to search for that, and just search for "usb audio clicks pops" or some such, you may find an odd post about someone having success after disabling the nVidia driver... and maybe even a buried post about PowerMizer... but you will be doing much more digging...) So after going into the nVidia control panel and changing the power management setting to "Prefer maximum performance," the clicks now match the level of the old Belkin hub (once every few hrs at most) without the hub. Note that this does not completely shut off Powermizer. There are tools (and registry settings) that do that and you can find those on the web. There's a GPU-Z utility to help you monitor your GPU. This fixes most pops. It isn't a 100% solution. Maybe every 2-3 hours there will still be a pop (probably due to other issues). Nevertheless, this observation is so obscure, that I thought I would post this for the benefit of others.

I cannot explain why the old Belkin hub and the hub built into my Dell LCD helped. But the HP laptop is also an nVidia graphics chipset whereas the Lenovo laptop is an ATI graphics chipset, so that confirmed a common thread.)

Note that the pops didn't completely go away with just the M1A DAC and the nVidia fix. Including the VLink 192 DDC proved to be a 100% solution. It is a much better USB audio chipset, provides Galvanic isolation, support for 192 kHz (useful when I get more 192 kHz music), etc. There were zero pops with the VLink in place, under any setting -- from Safe to Minimum latency. (Since I am so pop-paranoid, I kept the buffering on Safe. My back-of-envelope calculation shows that Safe is only a 20-25ms lag, which I do not believe the ear can notice.) I decided to keep it. There remains one issue though -- the stuttering after the PC has been idle for a while.

So how to fix the stuttering after idle on the VLink 192? I discovered that resetting the default audio device, even to itself, would somehow reset the driver and fix things. There's a command line tool that can set the default audio device. It works on Windows 7 and 8 (tested), so good enough for me. You can get the IAmAI/AudioEndPointController from GitHub here. I set up Task Scheduler to run it every 10 minutes, resetting the default device if no audio playing (and also force a reset when I logon or unlock a session, just in case). There is a slight drop out (but no loud click) when forcing a reset while audio is playing.

I have modified the code to provide a prettier display and to support these modes of operation by passing in:

• -1 to mean reset the default audio device to the current default audio device if there's no audio playing over a 50 ms window. Note that if something is playing in exclusive mode (e.g. WASAPI), setting the default device has no ill effects (i.e., no dropouts), so -1 does not bother to check for exclusive mode.
• -2 to mean force reset the default audio device to the current audio device

The stutter fix also fixed the freezes with the VLink 192. With the VLink 192, the nVidia PowerMizer fix is not needed. (Previously, this was an open question, but after running for many days with PowerMizer on, I can now conclusively say that the reset stutter fix, by itself, is sufficient.)

On USB cables -- I still don't subscribe to the school that they make an audio difference assuming the DAC or DDC has good jitter characteristics. But if it's longer than a 1 meter cable, go with a higher quality one because there are some dodgy cables out there! $30 to $50 is probably OK to spend, but $100 would be a bit silly in my opinion.

A Final Comment About Musical Fidelity

I am also quite disappointed in the quality of the USB interface on the M1A DAC. Two points:

1. The ground loop hum in some setups that the VLink 192 DDC fixes -- would it cost so much to add Galvanic isolation to the M1A DAC's native USB?
2. The stuttering issue of the VLink 192 DDC along with the overall pop issue -- It's true that the popping is somehow related to nVidia's Powermizer, but it is also true that it is fixable, probably in software with more buffering as the VLink 192 never pops. (It could be the XMOS chip, but I suspect software buffering more.) Also the stuttering is clearly a VLink 192 driver software issue. If you are in the business of PC audio, you need to invest more in PC software skills! The VLink 192 licenses the thesycon driver base (which seems to be the case with every DDC or DAC based on the XMOS chip). Clearly the stuttering can be an issue pushed back to thesycon for a fix. This shows a lack of listening to customer issue reports (clearly) and also a lack of extensive testing on various hardware/software combos. I can't be the only person experiencing these issues.

I will say, however, that some of Musical Fidelity dealers, including ListenUp and QAudio, are quite friendly and tried to be helpful, though the complexity of this issue was clearly not something I would expect them to actually be able to handle. This is the kind of complexity that only the manufacturer will (at least, should) have enough expertise to address.

So, based on acoustics, I will definitely stand by and recommend Musical Fidelity products (specifically, the M1A DAC and VLink 192), but for my next upgrade cycle, I will likely have a bias in favor of other manufacturers, even if they cost more for the similar performance. It's true that these are not $5000 components I bought, but having spent $1150 or so, it is fair for me to expect better. I have dealt with other manufacturers of audio gear where one of the designers is likely the person who responds to technical inquiries. This is still sufficiently high end niche products that a higher quality experience is to be expected. (In retrospect, I should have tried an April Music Stello U3 for the DDC. Honestly, I was tempted and didn't mind the ~$100 price difference though some may think $500 for a DDC to pair with a $725 DAC is silly... What stopped me was the difficulty of sourcing one to be delivered within 2 days. Now I am quite curious as to whether it's fundamentally a bug with thesycon drivers that every XMOS-based DDC may have...)

In all fairness, I suspect that asynchronous USB audio, while it has been available for approx 4 yrs now, is still immature and audio equipment manufacturers may not have enough PC expertise. But really, ignoring customers who like your product and just want to get them to work flawlessly is not a good way to keep customers... But I created this page primarily to help others who may be experiencing similar pops and clicks, so, enough said about customer service.

Raymond Lau
August, 2012