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IT & Systems Management

USB DAC: Six compact components for upgrading your computer's audio

I've got some bad news: Those nice headphones and great speakers that you spent so much money on? They probably don't sound as good as they could. You spent the time searching for the best audio gear for your computer, and no one wants to get less than what they paid for.

Not sure what I mean? Let me explain. Sound that you play on your computer starts out as a digitally-encoded stream. The built-in digital-to-analog converter (DAC) in your computer converts those bits of data into an electrical signal that is, in turn, fed to the amplifier that makes the drivers in your headphones or speakers move and produce sound.

But by its nature, this digital-to-analog-conversion process isn't exact, so some DACs produce a higher-quality facsimile of the original recorded signal than others. The DAC built into your computer was likely chosen to fit space, power, and cost constraints, rather than for optimal audio performance. And your computer's built-in headphone amplifier, which is part of the headphone jack's circuitry and provides the juice that drives your headphones, was picked for similar reasons--and has similar drawbacks. Plus, these components are all sensitive to the sorts of electronic noise that pervade the inside of a modern computer.

If you've invested in quality headphones or upgraded your speakers, you can use an external DAC to help those components reach their full potential; many external DACs also include significantly better headphone amplification--you use the DAC's own headphone jack instead of the one on your computer. These upgraded headphone jacks give you tighter and stronger bass, increased clarity and detail, better separation of instruments and notes, and other subtle improvements that add up to an increased sense of pace and musical drama. Taken together, these changes bring you closer to your music.

Inconspicuous offerings

Though many vendors offer large, AC-powered, audiophile-grade desktop DACs and headphone amplifiers, the best values for computer-focused DACs can be found in compact packages--the size of a deck of cards or smaller--that receive audio and power from your computer's USB port. I previously reviewed Arcam's $249 rPAC (4.5 of 5 rating), which impressed me with its build and sound quality. However, a number of similarly sized and priced models compete with the rPAC, meeting or beating its price, size, features, and/or sound quality.

I gathered six such products, ranging in price from $149 to $300. (My guideline: Don't spend more on a DAC than you did on the partnering headphones or speakers.) Each is small, uses USB for power and digital-audio input, includes a headphone output with analog volume adjustment (controlled via hardware or software), and supports high-resolution audio files up to a 96 kHz sample rate and 24-bit depth (some support 192 kHz/24-bit). Most are based around asynchronous USB technology, in which the DAC controls the rate of date transmission from the computer in order to reduce timing errors (called "jitter") that can cause audible and measurable reductions in sound quality.

The basics

All the models I tested are essentially plug-and-play: You simply connect the DAC to a USB port and your computer automatically detects the component and routes audio through it. (If your computer doesn't automatically switch audio output to the connected DAC, you can perform the task manually in your OS's audio settings.) If you've got a Mac and you're going to be playing high-resolution audio, you'll also want to configure your Mac for high-resolution playback (though whether high-resolution offers audible improvements is a controversial matter).

With all these models, you set the volume level in your music software (such as iTunes) to maximum to ensure that the DAC gets an unadulterated digital signal. All models except the CEntrance DACport and the Cambridge Audio DACmagic XS use your computer's software volume setting to control the DAC's internal volume. (On my Mac, the default volume-control increments were often too coarse, particularly for sensitive headphones. Holding down the Shift and Option keys while pressing the volume-up or -down key results in quarter-step adjustments.)

The HRT MicroStreamer and Meridian Explorer offer 3.5mm fixed-level line output (for use with speakers or stereos with their own volume control) in addition to the volume-controlled headphone output. You'll want to be sure to not plug your headphones into the line-out port, as the higher output level could damage your headphones, or, worse, your ears. It's easy to do this accidentally, so plastic headphone port caps are a good way to protect your equipment and hearing.

Over the course of my testing, I used each model both during my regular listening sessions, and while auditioning headphones for other reviews. For direct comparisons, I used my full-size home stereo and my two reference headphones: the full-size, open AKG K701 (currently available as the $349 Q701), which is particularly picky about amplification, and the $1099 JH Audio JH13 Pro FreqPhase custom in-ear-canal headphones, which can be difficult to drive due to low impedance. I also compared the DACs to the full-size DAC I use in my home stereo, Cambridge Audio's original DacMagic (discontinued, but $429 when last available; 4.5 of 5 rating).

CEntrance DACport

CEntrance isn't a household name, but the company has long been producing technology for digital-audio interfaces made by other consumer and professional audio companies. CEntrance's $250 DACport, originally released in 2009 (at the much-higher price of $400), is the oldest product here. Its small, simple design--an aluminum tube with a Mini-USB port on one end, a 1/4-inch headphone/line output on the other end, and the rest of the electronics housed in between--made a splash upon its introduction. In the middle of the cylinder is a rubbery, pencil-eraser-like volume knob. The DACport's aluminum shell is substantial, making the device feel like high-end gear. CEntrance also includes a carrying pouch, a USB cable, a belt clip, and a 3.5mm-to1/4-inch headphone adapter. (A $200 DAC-only model, the DACport LX, omits the built-in headphone amplifier and volume control.)

The DACport's technical capabilities and sound quality were as notable as its form factor back in 2009, kicking off the current generation of highly portable, high-quality, high-resolution USB models. One of the DACport's features is still unmatched by its newer competitors: Its headphone amplifier is based around a Class A design, which proponents argue produces better audio quality than Class B and D designs. This approach also means that the DACport is less energy-efficient, as power not used to drive headphones is converted to heat--the DACport gets warmer than the other units here, though never outright hot. However, while other models in this roundup use asynchronous data transfer, the DACport uses adaptive transfer--in which the computer controls data transfer, potentially increasing jitter--but in combination with the company's proprietary jitter-reduction technology.

AudioQuest DragonFly

Following the DACport by a few years, AudioQuest's $149 DragonFly takes the DACport's basic topography--USB input on one end, and a 3.5mm headphone jack on the other--and further shrinks and simplifies it. A standard USB plug is integrated into the unit, allowing the DragonFly to plug directly into a computer like a thumb drive. (Indeed, the device looks essentially like a thumb drive.) The DragonFly also eschews a physical volume control, relying instead on the host computer's software volume setting. A recent hardware revision, to version 1.2, included some improvements to the device's audio circuitry.

The DragonFly, designed in cooperation with DAC expert Gordon Rankin of Wavelength Audio, is charmingly small, well-built, and offers impressive performance. Despite its small size, the unit feels substantial, and it has a pleasant-to-touch rubbery exterior. The DragonFly logo on the outside lights up to indicate (by the color of the light) the current sample rate (up to 96 kHz/24-bit). AudioQuest includes a leather carrying pouch and a cap for the USB connector.

Due to its thumb-drive-like design, heavier headphone or interconnect cables can cause the DragonFly to strain your computer's USB port, so the company also sells the $17 DragonTail: a short USB extension, based on the company's Carbon line of high-end USB cables, that also prevents the DragonFly from blocking tightly-spaced ports on your computer.

The DragonFly's small size and all-in-one design make it a particularly good match for use with a laptop on the go. Thanks to this convenience, I frequently grabbed the DragonFly for portable listening.

Meridian Explorer

Meridian is a big name in the world of digital audio, and in 2013, the company jumped into the portable DAC/amp market with the $299 Explorer. The Explorer is an ovular, aluminum tube, closer in size to the DACport than the DragonFly, but much lighter; a flat, rubberized underside helps the device stay in place. Like the DACport, one end of the Explorer features a Mini-USB input, while the other hosts a software-volume-controlled, 3.5mm headphone jack. The output end also features an auto-switching 3.5mm analog/digital output, much like the one on most of Apple's recent computers. You can use the analog output to connect to a full-size stereo or powered speaker system; the optical output lets you use the Explorer as a high-quality USB-to-optical converter, so you can connect your computer to a higher-end DAC that lacks USB input.

Along the top of the Explorer are three white LEDs that indicate whether the sample rate is 44.1/48, 88.2/96, or 176.4/192 kHz--the Explorer is one of two models I tested that support this last rate. Meridian includes a short USB cable and a carrying pouch.

High Resolution Technologies MicroStreamer

High Resolution Technologies (HRT) made a splash in the hi-fi DAC market a few years back with inexpensive designs that nevertheless offered high-quality USB-audio inputs at a time when many DACs included this feature only as a toss-in afterthought or an expensive add-on. The company's latest model, the $190 MicroStreamer, is its most portable.

The MicroStreamer is a plain, but well-made aluminum box, slightly larger than the DragonFly, with a Mini-USB input on one end and two 3.5mm audio outputs on the other end. As with the Explorer, one of these is a line-level output for connecting to an audio system, while the other's level is software controlled for use with headphones. Along the side are a series of LEDs to indicate the incoming sample rate (44.1, 48, 88.2, or 96 kHz), and whether or not the unit is muted (via software). HRT includes a USB cable and carrying pouch.

The MicroStreamer's firmware can be updated over a USB connection to a Windows PC; a recent update brought a cool new feature: the capability to use the MicroStreamer with iOS devices. The iPad--and, as of iOS 7, the iPhone and iPod touch--unofficially support USB DACs via Apple's Camera Connection Kit USB adapter or Lightning to USB Camera Adapter, but only if the device's power draw is 100 mA or less. The MicroStreamer's version 1.2 firmware reduces power draw to 98 mA, making it the only bus-powered DAC I've found that works with a direct connection to an iOS device (more on iOS compatibility in a bit). This change in power draw also benefits people with Android devices that support USB On The Go.

Audioengine D3 Premium 24-bit DAC

Audioengine has made a name for itself with its excellent powered monitor speakers, which have become popular as alternatives to computer speakers, iPhone/iPod docks, and even small home stereo systems. The company also offers a line of high-quality electronics, including the N22 desktop amplifier and the brand-new, $189 D3 Premium 24-bit DAC headphone amplifier and DAC.

The D3 mimics the DragonFly's thumb-drive form factor. The D3's attractive, brushed-aluminum case sports two LEDs: One indicates power, and the other indicates a high (88.2 or 96 kHz) sample rate. The D3 comes with a carrying pouch and a 1/4-inch-to3.5-mm headphone adapter. (The company also makes the older, $169 D1 Premium 24-bit DAC, which is larger but offers an optical-digital input, RCA outputs, a hardware volume knob, and 176.4 and 192 kHz capability).

Cambridge Audio DacMagic XS

I mentioned above that Cambridge Audio's now-discontinued DacMagic is my reference DAC in my home stereo system, and it continues to impress me after four years of ownership. So I was excited by the company's recent introduction of the $190 DacMagic XS, a small, USB-powered DAC that competes with the other models here. The XS most closely resembles the HRT MicroStreamer--it's a small, black, aluminum box with a Micro-USB input on one end and a 3.5mm headphone jack on the other. On top of the unit are volume-up and -down buttons. A LED glows during playback, with different colors corresponding to 44.1/48 kHz, 88.2/96 kHz, and 176.4/192 kHz sample rates. (Playback of 176.4/192 kHz files requires setting the unit to Class 2 mode by holding the volume buttons for a few seconds. This distinction isn't important on the Mac, but for Windows, Class 2 operation requires the installation of a special driver.)

The importance of impedance for headphone listening

Electricity is a complex thing (literally--it's described using complex numbers), and the interaction of the electrical characteristics of a headphone amplifier and connected headphones, quantified by impedance, can alter the resulting sound. Using devices with compatible impedance ensures that the drivers on a particular set of headphones are properly controlled and that their frequency response isn't altered. A rough rule is that a headphone's impedance should be at least eight times the impedance of the amplifier. However, this estimate isn't universally agreed upon, and low-impedance headphones will still work with the higher impedance amps, though often with flabby bass and altered frequency response.

The MicroStreamer, DacMagic XS, and DragonFly (as well as the previously reviewed Arcam rPAC) have an output impedance of around 0.5 Ohms, so they'll partner well with headphones with impedance of 4 Ohms or higher. This means that these products are suitable for low-impedance headphones such as many in-ear models. The Meridian is rated at about 5 Ohms, making it borderline for use with lower-impedance in-ear models, while the DACport and D3 are rated at 10 Ohms, so they're ideally suited for higher-impedance (80 Ohm or higher) full-size models. (CEntrance can optionally modify the DACport, if you request, to reduce its impedance to 1 Ohm.) But, again, the 8:1 recommendation is just an estimate, so if you're in doubt about a particular pairing, the best thing you can do is test a particular device with your favorite headphones before committing to purchase.

Listening in: DACs alone

In my testing, I found all of these models to be solid performers. If you aren't listening side by side, it's tough to discern major differences--even comparing their performance directly is to some extent splitting hairs. But a review like this is aimed at such comparisons, so let's split some hairs!

I conducted my first comparative tests using my big rig (my home stereo) in order to evaluate each unit's DAC apart from its headphone circuitry. I started with the Audioengine D3 (which, prior to the DragonFly's recent price drop, was the-least expensive model), using it to establish a baseline level of performance. Compared against the D3, the DacMagic XS sounded more timid: It was less well-defined, and it didn't sound as sharp. Bass, in particular, seemed quieter and looser through the XS.

In contrast, the MicroStreamer showed an improvement over the D3. The MicroStreamer fleshed out the sound, adding stronger, tighter bass; more clarity and detail; and an improved sense of rhythm and pace. All three of these units, priced around $190, sound good, but the MicroStreamer offers the best sound quality at this price.

Comparing the MicroStreamer to the DragonFly revealed obvious differences, but choosing a favorite was more difficult. On first listen, the MicroStreamer seemed clearer and more detailed, while the DragonFly had a smoother, more-natural sound that wasn't as instantly impressive, but that I preferred over longer listening periods. Ultimately, the DragonFly's smooth presentation gave instruments an "in the room" aspect, whereas music played through the MicroStreamer sounded more like recordings. I personally tend to prize clarity, detail, and accuracy over a smooth, romantic sound, so I would have expected to prefer the MicroStreamer, but nevertheless I found the DragonFly to sound more satisfying.

Sonically, the DACport resembles the DragonFly more than the MicroStreamer, but its DAC performance doesn't quite match that of either of those units. In my testing, the DACport lacked the clarity and detail of the MicroStreamer, but it also didn't sound quite as natural as the DragonFly. It did manage to best the D3 and the XS, though.

The Explorer also resembles the DragonFly more than the MicroStreamer, but unlike the DACport, the Explorer bettered those DACs. In my listening tests, the Explorer offered a fuller, more-realistic sound than either, and it gave music a more-driven, exciting feel than the DragonFly--it was clearly the best of these DACs. On the other hand, the Explorer couldn't match the performance of my reference, the full-size DacMagic, which made the music sound better-defined and even more in-the-room. I found the difference between the full-size DacMagic and the Explorer to be more dramatic than the difference between the Explorer and the other portable models here. In other words, while the portable, computer-focused DACs tested here can do double duty in a traditional stereo system, traditional stereo components don't struggle to outperform them.

In summary, when it comes to just the DACs of these units, I liked the Explorer the best, followed by the DragonFly, the MicroStreamer, the DACport, the D3, and then the DacMagic XS. I also reconsidered the Arcam rPAC, which I'd slot in between the DragonFly and the MicroStreamer. The rPAC has a more full-bodied, believable presentation than the MicroStreamer, but sacrifices some clarity and speed versus the DragonFly. It doesn't match the portability of either model, however.

Listening in: With headphones

I then tested all the products using headphones in order to evaluate each unit's combination of DAC and headphone amplifier. Listening through the JH13 in-hear headphones, I came to similar conclusions in terms of sound quality and relative rankings, although the differences between products weren't as pronounced as they were through my stereo. I did notice looser bass in the D3, DACport, and Explorer, likely due to the relatively high impedances of these units in combination with the relatively low impedance of the JH13. However, these changes didn't alter my overall preferences.

The AKG K701 is less picky about impedance than the JH13, but more picky about amplifier power and quality. Most of my comments in the previous section hold, though the DACport and rPAC's better headphone amplifiers assert themselves with the K701--both made these headphones sound more lively, offering tighter bass and better definition in the mids and highs. With the K701, the DACport and the rPAC best even the Explorer--keep this in mind if you're using full-size headphones that are difficult to drive.

USB-to-optical bridge

As I mentioned, the Explorer has an optical output, which can be useful for bringing an optical-audio output to computers (such as the MacBook Air) that lack it--or, from the opposite perspective, for adding high-quality USB compatibility to other DACs that lack this feature (or have older, lower-quality USB inputs). I used the Explorer to ferry USB audio into my full-size DacMagic's optical port, and I then compared the result to a direct optical-to-optical connection between my Mac and the full-size DacMagic. I detected no difference in audio quality between the two configurations. In contrast, I find the DacMagic's USB input lacking compared to its optical port, so I also compared the full-size DACmagic's built-in USB input to the Explorer/DacMagic combo: In this configuration, the Explorer handily bested the full-size DacMagic's mediocre USB input--USB audio interfaces have improved substantially in the last five years! If you have a use for it, the Explorer's USB-to-optical bridge feature is a great way to ensure that a high-quality but USB-deficient DAC remains useful.

Phones and tablets

Finally, I tested the MicroStreamer (running the new, lower-power firmware) with an iPad mini, an iPad mini with Retina Display, an iPhone 5, and a third-generation iPad using Apple's iPad Camera Connection Kit and Lightning to USB Camera Adapter. All three sounded great when listening to high-quality audio files, handily besting the devices' built-in audio circuitry. And the MicroStreamer is portable enough that I've made extensive use of this capability. I was even able to use iTunes Home Sharing to stream 96 kHz/24-bit files from my Mac to the iPad mini under iOS 6. (Unfortunately, under iOS 7--at the time of this writing, iOS 7.0.4--playback stuttered, which I'm assuming is a bug in the OS.) I did notice that the MicroStreamer's power draw had some impact on battery life: I lost a couple hours of playback time on my iPhone when using the MicroStreamer in this way.

As I mentioned previously, none of the other models here work connected directly to Apple's adapters, but they do work when connected via a powered USB hub. This is a nice option to get high-quality sound from an iOS device at home, but it's obviously not particularly portable.

What about Android devices? Well, it's complicated--perhaps unsurprisingly. If your device supports USB-on-the-Go, these DACs may work. When I briefly tested the DACs with the Samsung Galaxy Note 2, only the MicroStreamer worked immediately. I've seen reports of other devices working, particularly with third-party software. If you'd like to know if your Android hardware and software will work with one of these DACs, my best advice is to do some research--this post (and thread) on Head-Fi is a good place to start.

Bottom line

A few years ago, any of these models (along with Arcam's rPAC) would have been best-in-class. You really can't go wrong with any of them--each provides great sound quality and will improve on your computer's built-in audio hardware. The differences between them can seem subtle, particularly if considered in isolation. However, the Meridian Explorer offers the best audio quality overall, befitting its $300 price, and its optical output can be useful. The AudioQuest's $149 DragonFly offers the next-best overall sound quality, and the fact that it does so at half the price of the Explorer makes it the best value here. That value, combined with the DragonFly's convenient design, make it my favorite model overall.

In a few cases, however, I would recommend other models over the Explorer or DragonFly. HRT's $190 MicroStreamer almost matches the DragonFly's sound quality and price, and some listeners may prefer its clear sound or find its cool iOS compatibility worth the price premium. If you primarily listen to difficult-to-drive, full-size headphones, the CEntrance DACport and Arcam rPAC will outperform even the Explorer with those headphones, and each costs about $50 less. The Arcam has the better DAC, while the DACport has the better amp.

While I liked both the Audioengine D3 and Cambridge Audio DacMagic XS, it's difficult to recommend them given that each is more expensive than the DragonFly but neither matches its sound quality. However, the DacMagic XS is the least expensive model that plays 192 or 176.4 kHz files.

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