Hi everyone. As I promised, here is my review and report on performance of Audioquest Jitterbug (AQ) and Uptone Regen USB conditioners. I had bought the AQ and Michael (Dallasjustice) was kind enough to loan me the Regen. Before I get into the meat of this review, some key notes:

Note 1: This is posted in the science thread. So please don’t post that “but my ears say otherwise.” We already know that and subjective reviews have generally been positive on these products. This assessment is designed for the most part to be objective although since I was asked, I will also post some subjective expressions.

Note 2: The information in this post is entirely mine and not the position of WBF Forum.

Note 3: I am not a professional reviewer. I did these tests because I was curious. I make no assurance to accuracy of any of it. It is entirely possible that my test setup is screwed up even though I have repeated them a couple of times to increase confidence in them. If you are one of these manufactures and have data that disagrees with what is posted here, please share them.

Note 4: The test data here is specific to my setup. It is possible and indeed likely that other sources and DACs would act differently. I personally don’t think the overall picture and message will change but I can’t represent that without testing a lot more equipment.

Note 5: As a reported a week ago, my dog “unboxed” the AQ by chewing off its case. Electrically it seems to be intact and it functions by passing through the USB bus. While there is a slight chance that it no longer does what it is supposed to, I think the chances of that are very low.

Executive Summary
There is a lot of data here so I thought I give you the punchline for the less than patient . In a nutshell, I cannot back any positive reports of these products. At best they do nothing, at worse they add tiny amount of (inaudible) distortions of their own. There are some interesting twists and turns here so I hope you read the rest of the article.

The class of product attempts to clean up/precondition the digital USB bus on the way to your DAC. USB is a simple bus. It has a ground and power line which can supply energy to downstream devices. It also has a pair of lines that are used to transmit and receive data. Being a predominantly digital computer interface, manufacturers are under no obligation to provide laboratory level of precision in either supply power it provides or perfectly clean signals. Compliance tests focus on reliable data communication and that is it. So in theory, cleaning up this type of interface can provide useful gains and hence the creation of this new category of products.

Expanding the last point, computers are noisy devices and some of that noise rides on USB power lines and its signal. If the DAC does nothing to clean up such signals, then it is possible for them to bleed into the DAC. Timing of the USB bus can also change due to noise and if a DAC uses synchronous (lousy) mode of USB operation, it could be impacted negatively.

Here is the strong counterpoint though. We are in domain of “what is best” in this forum. I sure hope anyone buying a DAC is getting one where the designer knows very well that these issues exist and has already put the few cents or dollar or two worth of parts that these products have. As such, I personally don’t expect any high-end DAC to benefit from these products. If any do, I would question the DAC company before resorting to dangling a device like this in front of them.

Anyway, theory is one thing but the proof of the pudding is in backing it with objective data. In this situation, I used my everyday laptop which is an HP Zbook 14. This is a “professional workstation” aimed at high productivity/CAD workers. It cost me $2,200. So not some cheap $300 machine here. I do a ton of listening tests on this laptop and find its audio performance to be good. In this scenario the laptop is feeding the DAC either directly (which I call “nothing”) or through one of these two devices.

Test Setup
I came up with three sets of tests. It is important that you read this section carefully as otherwise you will be lost in a sea of seemingly similar graphs. They are very different and test different things:

1. Filtering of USB power line. I took a USB cable and cut one side of it off. I stripped the wires and then fed that to a “differential probe.” This is a $300 device that acts like the balanced connection on your audio equipment. It rejects common noise that exists all around my test gear from my laptop to different instruments. While it doesn’t guarantee perfect results, it goes way beyond using a simple probe.

The output of the differential probe (which divides the signal by 10) is fed to the BNC input of my Audio Precision Analyzer. I then use a simple FFT to check for the spectrum of the power line. Use of an audio analyzer here is unorthodox as usually a much higher frequency spectrum analyzer is used. Those analyzers unfortunately do not have high precision. And at any rate, we care about seeing the spectrum in audioband and thereabouts. What exists at many megahertz may have some audible impact but I rather know what is happening that our audio equipment can reproduce.

If these devices completely filter the power line, it should be a flat line at the limit of the analyzer.

2. These next two tests go to the heart of the matter: what the DAC puts out. At some level it doesn’t matter what is going on before the DAC. The proof is what we feed to our amplifier which is the output of the DAC.

In the first instance of this test, I simply look at the output of the DAC when nothing is played. In other words, look at the noise floor of its output. As with Test #1, I show both wideband response to 130 KHz and also limited to 24 Khz.

3. For this test I feed the DAC a J-test signal at 48 Khz sampling. J-test looks like a 12 Khz tone in such a graph. Anything else other than a sharp single spike is noise, jitter or other types of distortion created. An idea DAC would have just a spike at 48 KHz and nothing else. Here I show this spectrum both wideband and audio bands.

The most impact from such devices would be in low cost, USB powered devices. So I tested with the only one I have currently which is the Meridian Explorer DAC. This is a few steps above in performance that Chinese $10 USB sound cards. And the minimum level of performance that I imagine members here would use.

Test 1: USB Power Filtering
So let’s dig in. Here is the Audioquest Jitterbug (AQ) versus straight wire connected to my laptop USB port:

Before getting into the comparison, we see that the laptop USB power does have predicted impurities. Those specific peaks are functions of events inside my laptop running at those frequencies. The tallest one is in the middle at around 52 Khz.

Note that the problem is not as bad as it seems. I have set the vertical scale to -80 dBFS. So this is highly amplified graph. All the other spikes other than the center one are actually below the noise floor of CD/16-bit audio.

Sadly we see that the AQ does nothing for us here. The minor changes are not consequential and the overall picture remains as if we had not used this device.
Let’s now compare the cable to Regen:

Now we are talking. All the tones are gone and the noise floor lowered. This makes sense since Regen provides its own power so what comes out of my PC is inconsequential. In this regard, the Regen is performing something compared to AQ which did nothing.

Test 2: Noise floor of the DAC output
If the computer is electrically coupled to the DAC, one would expect noise to travel to the downstream devices. Let’s look at that and compare it to AQ looking at spectrum up to 130 Khz:

The AQ spikes in green strangely seem worse than piece of wire. It is hard to know the reason for that but clearly nothing good is being done here.

The situation is even worse for the Regen!

Now, these are again at pretty low amplitudes and the vertical scale is highly exaggerated. But one wonders how devices that are supposed to reduce noise, are actually increasing them.

Test 3: Jitter Response
One of the advertised features of these devices is reduced jitter. Usually that is stated in the form of reduced jitter on USB bus but such reduction is not of interest to us (and at any rate is not substantiated by the manufacturer with measurements). What we care is jitter coming out of our DAC. To that end, let’s look that output and compare with and without AQ:

Apologize for the darkness of the graph. What we see there is no difference with insert of AQ. Whatever jitter the Meridian DAC puts out normally is there just the same. As is the noise floor.

Let’s now look at Regen:

Now this is really strange. We now have new distortion spiked in red once we inserted the Regen in the path!!! Again the levels are very low but what the heck? A device implying that it reduces such distortions actually increases them? The Regen uses a USB hub so it is possible that this chip has worse USB performance than one in my laptop.

Let’s zoom into audio band and see if the picture is any different with AQ:

Good news and bad news is that the AQ did nothing in frequencies below 24 Khz. No damage but no improvement either.

Regen on the other hand, did add some distortions:

And this time it seems to be correlated jitter (or modulated reference voltage) at 4 Khz, causing two sidebands at 12-4 = 8 Khz and 12+4 = 16 Khz. Again, the levels are very low but what good is a device that didn’t attenuate any of our problems and added a couple of spikes of its own???

UPDATE: further testing later in the thread with a lab linear power supply and Regen showed this:

We see that the 8 Khz distortion tone has disappeared and the one at 16 Khz reduced too.

So let's compare the Regen with Linear Power supply and nothing in line:

Other than a tiny potential improvement at 16 Khz, there is really no difference to speak of here. In this sense, a Regen with linear power supply becomes like AQ. That is, showing no evidence of improvement in DAC output. All the distortions that were there without these devices, are still there with these devices.

Objective Analysis Summary
Simply put, there is no good news here. Both devices degraded the performance of the DAC a bit and did nothing to improve it. There are reasons for this that I won’t go into but let’s be careful in using our intuition that when something is “filtered,” it is always good. That is not how this interface works.

Subjective Listening Test
I tested the AQ both in “parallel” and “serial” modes. In parallel mode you just plug it into a port next to the one you are using. Doing that to my Berkeley and Audiophilleo USB to AES/S/PDIF to my Mark Levinson DAC did nothing. This was easy to test since it does not interrupt the flow of music.

Testing in “serial” mode was much harder since it would naturally stop the music from playing. Fast switching/comparison was not possible. I tried anyway and couldn’t hear a difference for what it is worth.

I then tested the Regen. Once again, comparison is hard and next to impossible due to multi-second switching. On first insertion, I thought I heard an improvement. I went back and forth and the tables turned and no Regen sounded better . In other words, the differences imagined or real, are well within placebo range.

I know we have had our differences before in how audio equipment is evaluated. For those of you sold on these products, I like to implore you that you go into this evaluation with a skeptical mind. Don’t assume that any of the technical explanations given are supposed to improve things. Data here clearly shows that our intuition here is not correct. The circuit theory is much more complex and don’t lend themselves to conclusions we draw. Assume that the device could as well hurt the performance as it can help. Then see if you can reliably hear an improvement.

For my money, I think a rock from the garden put on top of my DAC may do better than either one of these devices. For the price of Regen, you can buy 10 high-res downloads and I am confident that would bring more happiness to your music life than this device.

Comments and questions welcome .