MEASUREMENTS: Computer USB +5V Power Noise by Raoul Trifan & MQA's Bob Stuart Speaks Again...

Editor's Intro:

Hey there guys. One of the joys of running this blog has been the opportunity to meet some of you and connect through E-mail with folks from around the world with shared interests.

Every once awhile, I get the chance to see some of the measurements and work you guys have done. Today, I want to show you some work from Raoul Trifan from Romania.

In the last year, we've been in contact about his work with USB ports using the various computers he has at his disposal. What he's sharing today is literally the "tip of the iceberg" in terms of the data and measurements collected over the last while. He has done all kinds of other work with power supplies, modifying audio gear and such which I'll leave for future discussions.

Today, let's just consider the noise on the +5V USB line from computers:

Using a PicoScope 2204A, he has produced some interesting screen shots to consider with the various machines.

A Look At The Computer USB +5V Noise...

By Raoul Trifan

In high fidelity, we are aware that we should minimize the noise coming from our power supplies as this could improve the ultimate sound produced by the audio equipment. For example, Analog Devices has shown us how an AD9445 ADC can be affected by the ripple and noise created by removing the decoupling capacitors from its power supplies. So, indeed, very clean power does matter at a certain level, but just how much attention and money do we need to get into this may be up for some debate.

Because many audiophiles are spending money on USB power injectors and power cleaners, I decided to see how noisy the USB ports from some laptops I happen to have around here can be. I’m using for this test my PicoScope 2204A digital scope with its original probes, my Windows 7 and macOS Sierra desktops and a few laptops with the original power adapters and original lithium batteries. Some of the laptops having also their original docking stations available to measure. The machines are the Lenovo X201, Lenovo T430, Lenovo T440, HP2560p, HP8460p, MacBook Pro (mid-2012), MacBook Pro (mid-2014), iMac 27” (late-2013), and my DIY desktop computer based on the Gigabyte GA-B85M-D3H motherboard.

First, let's have a look at the Lenovo Thinkpad T430 with its multitude of ports:

As you can see, the vertical scale is in mV with each division line set at 10mV. Horizontally is time with each division line as 20μs. We can see the amount of noise in the DC power line fluctuation. For this computer, I like the left side 1st USB port and also the rear USB port (by the power connector), but I totally hate how dirty the power is on the docking station’s ports! Notice that the voltage fluctuations go above 30mV at times with the docking station. Definitely not recommended to connect your DAC into this docking station.

The next machine is the Thinkpad T440:

Similar to the T430, I like the left USB ports, but I do not like how the power on the docking station’s USB ports perform. Again, not recommended to connect your DAC into this docking station!

Moving along to the next Lenovo machine, this is the old Thinkpad X201 from around 2010:

Surprisingly, the old X201 has the best USB power from all tested laptops in this survey of devices! Again, the docking station seems to show a bit more fluctuation with spikes ~10mV in magnitude but even then you could probably connect your DAC without concern. That right side USB port looks excellent. Quite impressive results from an old device like this one.

Next is a Gigabyte GA-B85M-D3H motherboard used in my desktop machine and the desktop Apple 27" iMac from late 2013:

I’m impressed by the clean USB power from my DIY 4-years-old desktop with the Gigabyte GA-B85M-D3H motherboard when the rear USB ports (soldered onto the motherboard) are used. As for the wired front USB port, please don’t even try using these. Clearly the cheap USB connector and long cable connecting the motherboard to the front of the computer case is picking up noise from inside the case.

Given the audiophile perception (maybe general perception) that Apples are good machines for audio, I was hoping for a cleaner result from the late-2013 iMac, especially since the rear USB ports are soldered directly onto the motherboard (no USB cables involved). It looks like the ripple and noise spikes are not so good!

Despite the spikes from the iMac above, I was unable to hear any issues with the sound itself, but I had no time to do a detailed A/B comparison and have no decent ADC to run RMAA. Anyway, most likely any engineer designing audiophile products seeing the iMac’s USB power waveform above will probably recommend using a good external +5V power supply for the USB or a Y-cable with clean +5V injector.

Next we have a couple of HP notebooks - the Elitebook 2560p and newer 8460p:

The HP 2560p might not having the purest USB power ever, but it’s definitely much better than the bigger brother 8460p! Unlike the Lenovo computers, the HP docking station shows much lower noise level. This just goes to show that I cannot generalize and say that "docking stations are bad" because it obviously depends on the specific device.

As mentioned above, Apple has created quite a following and there are audiophiles who feel that the Macs are better for audio purposes than Windows-based options. To some extent this is understandable given that Macs are often rather quiet sounding machines and aesthetically more pleasing (especially going a few years back). But what about the USB port power noise level? Here are two MacBook Pro laptops:

As you can see, on the 2014 MacBook Pro the USB port near the power plug is noisier than the other port. Apple machines are clearly not special in any way in terms of power noise from what I can see. The Lenovo laptops have cleaner +5V on many of the USB ports.

Finally, let's have a look at a decade-old Fujitsu-Siemens Amilo Pro V3205:

The right side port from my old Amilo Pro is quite decent, too bad the left port is significantly poorer.  The rear port sits in between with the amount of noise seen on the scope.

Archimago's Thoughts and Conclusions:

Thanks Raoul for letting me show these measurements you've collected! As I mentioned in the introduction, Raoul has actually done a bunch of other measurements he has graciously shared over the last couple of years. It's great that someone out there has taken the time to measure the USB power line noise level from a selection of laptops and desktop machines to demonstrate the variability out there... Furthermore, it's interesting to see just the amount of variability between the different USB ports on the same computer. I suggest very obsessive "high end" audiophiles should break out the oscilloscope and check to make sure they're using the quietest USB port on whatever device they're using! :-)

I think this is interesting because after years of being told as audiophiles by the likes of AudioQuest (and their Jitterbug device) or the cottage industry of USB "cleaner" devices like UpTone (and their USB Regen) or iFi Audio and their host of "purifiers", there really doesn't seem to be much out there showing what the noise looks like or at what levels they are to be found from a typical computer USB port. I would have thought that measurements like these from USB ports would be part of the promotional material to demonstrate the "problem" and then the company showing how their devices clean up these voltage imperfections. Would that not be a "no brainer" from the perspective of marketing and public education?! Also, as usual, where is the audiophile press in all of this over the years to educate the hobbyists and buying public? Would it also not be nice to have simple USB power cleanliness measurements on very expensive audio computers like this ~£3000 Innuos Zenith or >£2000 Melco N1A/2 to double check that at least they're performing in ways superior to just a standard off-the-shelf computer?

Unfortunately Raoul noted that he has not conducted A/B listening tests and doesn't have an adequate ADC at this time to measure the effects these USB voltage anomalies have on the analogue output from USB DACs. From measurements over the years and as far as I can tell, DAC output does not appear to vary significantly with the machines I've used. At least I can say that I have found no measurable difference using even inexpensive DACs powered from the USB port like AudioQuest's own Dragonfly V1.2 awhile back, or the AudioEngine D3 - never mind the more expensive wall-powered USB DACs! There's other evidence of this littered throughout my measurements over the years beyond those 2 examples.

Hopefully at some point Raoul will do some measurements with his own DACs. For example, it would be very interesting using something like a Dragonfly plugged into the poor quality T430 laptop dock USB port and comparing the output with the relatively clean left USB port.  Since we know the noise level is much poorer with the dock, are we then able to correlate this with DAC noise levels for example? (Maybe someone wants to take on this little project! :-)

For now, as far as I can tell with my computers, even with inexpensive DACs these days, the power management and filtering is doing a good job without any extra help from audiophile accessories.

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Well, I see that the latest issue of Stereophile (June 2018) has been released in the digital subscription form. As you might expect, MQA is yet again discussed (I guess they just have to keep it in the minds of audiophile consumers for some reason). At the time of this blog post, I have not seen the article released online yet (I'm sure it will since it is very much a "message from the manufacturer") [it's posted now]. This time, Jim Austin writes yet another MQA Q&A with Bob Stuart's comments.

Not unusually, some more terminology gets mentioned - this time B-spline interpolation is tossed out for the reader to consider and they're talking about the "center of gravity" being in the right place in regard to temporal accuracy. There is acknowledgement also of both aliasing and imaging present with MQA but of course said to be inaudible. I don't know about what you guys are perceiving but there does appear over time to be a softening of how actually "revolutionary" this technology is; rather than bold and hyperbolic statements of greatness, it's now widely acknowledged as lossy and more of "yeah, we know there are things like imaging and aliasing... But it ain't all that bad... And the 'center of gravity' is in the perfect place".

I see that the only measurement offered is another FFT of one of 2L's tracks (2L-078). A new "improved" version of the encoding algorithm was done on the music with less noise compared to the DXD playback. So what? The FFT shows that the portion of the track they're demonstrating has no content above 23kHz! So maybe the new encoding may have utilized steeper filters to reduce ultrasonic leakage or maybe they applied lower dithering / noise shaping levels compared to before? Good to see that potential "bug fixing" can be done and there's flexibility in the processing I suppose. However, a simple downsample from DXD to standard 24/48 would have resulted in just as beautiful of an FFT (likely with an even lower FLAC-compressed bitrate)!

The final sentence of the article goes like this (about the "de-blur" and time smear claims):

This smear, we believe, can be material for the human listener who is extracting multiple cross correlations, as well as envelope and nonlinear measures of the audio.

I don't understand exactly what Mr. Stuart is claiming here; what "cross correlations" specifically? What "envelope"? Which "nonlinear measures"? Yes, the mechanisms of listening and hearing are complex, but would it not be good to be a little more specific? But the point remains that after all these years (and despite earlier in the article Stuart claims they did "hundreds of experiments"), at best he can say is that he "believes" what they did with MQA was helpful! Surely, out of these hundreds of experiments, he can spare just a little more information about what beneficial evidence they may have found. Given countless opportunities, it's rather clear that they've got nothing. And writers like Jim Austin likewise has nothing to add other than uncritically repeating company claims. At this point, I really hope the McGill University folks have something "material" to talk about (maybe some actual data by the Milan AES in late May?).

Well folks, MQA's marketing began to get heated a few years ago (eg. here and here) with Bob Stuart's Q&As and I hope it ends with his Q&As. Fascinating that there are not other technical "evangelists" talking in support of MQA. It always just ends up about Bob Stuart! It would be unfortunate if the legacy of Mr. Stuart is so strongly tied to this questionable (and IMO unnecessary) codec.

If in the days ahead, we see music companies and streaming services actually adopt MQA as a distribution format, I think it's pretty clear that this is in spite of public acceptance of the format rather than what companies would prefer to see - acceptance because of public demand.

This week, we were told that ESS has decided to incorporate MQA "rendering" into their DAC feature set. It looks like they're targeting this for "small and lower power solution" DACs meant for mobile devices and headphone users. Something like the Dragonfly Black rendering on-a-chip. IMO, with actual high performance DAC chips like the ESS 9018 and recent 9038Pro, it's hard to imagine why anyone would want to use those MQA upsampling digital filters on playback as they can only serve to reduce sonic fidelity from these high-end parts.

Anyone getting really tired of MQA yet? :-) I noticed that there was little talk of MQA at the AXPONA 2018 coverage and so far not much from Munich High End (just a couple new partners and their insistence that this represents a "growing momentum"). On the software side, I guess it's finally about time that Audirvana Windows version is released with software MQA decoding; about a year after the Mac. Also, Roon 1.5 now handles MQA including the ability to perform DSP on the unfolded data. Nice to see that MQA is relaxing not only the insistence on achieving "revolutionary" sound quality, but also on how rigidly they're "end-to-end" "authenticating" the playback chain... Yet again, why bother with all the hassle in the first place? I think it is good that Roon has MQA support now given the asking price and the fact that they're closely tied to Tidal. It would be rather unsatisfactory to pay quite a bit for the Roon service and not be able to access the much-hyped Tidal "Masters" feature!

Have a great week ahead folks! As you can imagine, I do quite a bit of keyboarding for work and blog writing of course. This past week I got a new mechanical keyboard; the Kingston HyperX Alloy Elite in my home office and its little brother the HyperX Alloy FPS at work. It has been awhile since I last used the clicky keys of the Cherry MX Blues (thankfully my wife doesn't mind)! I think the last time I owned a keyboard with Cherry switches was with my early generation Amiga 2000 computer in the late 80's :-). Nice to be back with a great tactile keyboard rather than the usual low-profile, shallow-travel "Chiclet" keyboards... In retrospect, I should have done this years ago!

BTW, for those who want something quieter, consider the Cherry MX Brown switches; still feels great with less noise. Also, one could dampen the MX Blue switch noise a little with <$10 O-rings under the key caps which I might do if the wife complains!

Until next time, enjoy the music everyone...