High Resolution Technologies iStreamer DAC (Playback 40)

Digital-to-analog converters
High Resolution Technologies iStreamer
High Resolution Technologies iStreamer DAC (Playback 40)

High Resolution Technologies (HRT) has built a series of affordable, high-performance USB DACs collectively called MusicStreamers, which have won critical acclaim from many high-end audio publications, including our sister magazines The Absolute Sound and Hi-Fi+. But with the release of its latest product, the $199.95 iStreamer, HRT has embarked on a new path by offering—you probably guessed this from the product’s name—a dedicated DAC created specifically for use with iPods, iPhones, and iPads.


Many of us embrace the idea that iPods, iPhones, and iPads are wonderfully convenient portable devices, but ones whose performance is—as a matter of practical necessity—limited (at least to some degree) by Apple’s inherently low-cost and relatively low-performance onboard DACs and analog audio sections. In short, music lovers who prize sound quality have long felt that a better sounding approach would be to pull digital audio data directly from the iPod/iPad/iPhone, and then to feed it to a higher quality outboard DAC fitted with superior analog audio electronics, which is precisely where the iStreamer comes in.

To be clear, the concept of extracting digital audio data from Apple’s portable devices for external processing is not a new idea. Several years back, Wadia’s Model 170 iTransport was the first digital audio dock for iPods, though the 170 required a separate, external DAC of the user’s choosing. Later, Peachtree upped the ante with its innovative iDecco integrated amp/DAC/dock, which not only extracts digital data from iPods, but also provides an excellent onboard DAC and integrated amp section. Other manufacturers, including Marantz, have built disc players with digital connections for Apple products.

But several things make the iStreamer unique in this product area. First, and perhaps most obvious, is the element of price. At $199.95, the iStreamer is the only Apple-compatible DAC that actually costs less than a modern-day Apple iPod Classic. In short, if you want a high performance DAC whose price is consistent with what you paid for your Apple portable, the iStreamer is—for now—pretty much the only game in town. Second, the iStreamer is noteworthy in that it doesn’t try to be all things to all people; it’s an Apple-specific DAC that handles all Apple-supported data formats, but that does not attempt to handle other formats not supported by Apple portable devices, which helps to hold costs down. Third, and this feature really constitutes the “special sauce” that I think helps this product sound unusually good, the iStreamer provides a host mode interface, meaning that the iStreamer takes complete control of the data exchange between the Apple device and the DAC for what HRT describes as “jitter free” performance (in other words, the data transaction is locked to the iStreamer’s—not the Apple device’s—clock).

The key idea is that the iStreamer is meant for owners of Apple portable audio devices who realize that better sound quality is out there, and who would like to access it without spending the proverbial arm and a leg. The iStreamer also caters to those who want a foolproof, plug-n-play, yet also quite high performance device that allows users to play content from their Apple devices through full-size stereo, home theater or desktop audio systems.

Is the iStreamer targeted toward Audiophiles with a capitol “A?” Yes and no. The iStreamer sounds very good for its price, but does not claim to be the best DAC available (HRT offers higher end models that go after that end of the spectrum). Instead, the iStreamer is for music lovers who love their Apple devices but want “something better” in the sound-quality department. On the other hand, the fact that the iStreamer provides a host mode interface gives it a sonic edge relative to most would-be competitors.


The iStreamer is extremely simple to use. You simply hook up the wall wart-type power supply, connect a left/right pair of RCA cables to your amp/receiver, and then hook up a traditional Apple-type docking/USB connector. Once you flip on your Apple device, one of the iStreamer’s three data rate lights (32k, 44.1k, or 48k) will start flashing—denoting that the iStreamer is synced to your Apple device—and you’re good to go.

There are a several small caveats to note:

•The iStreamer is not portable (it’s tethered to its wall wart-type power supply).
•The iStreamer does not provide digital audio outputs, so that there’s no way to use it as a digital dock to feed data to an outboard DAC.
•The iStreamer can be sensitive to the condition of the Apple dock/USB cable, so that you’ll want to make sure the connectors are in good shape and correctly inserted on the Apple end (the iStreamer may not be able to achieve or maintain proper sync if the connector is seated askew in the Apple device).
•In a break with the common practice, the iStreamer’s data sync lights flash on and off continuously when sync is achieved (for most other DAC makers, a flashing light indicates that the DAC is trying to sync, while a solid light indicates that data sync has successfully been achieved).
•Finally, note that while the iStreamer supports many Apple devices (as listed below), it does not support some of the earlier generation iPods (I believe because they may not support the iStreamer’s required host mode interface).

None of these caveats constitutes a “showstopper” by any means, but they are certainly points worth bearing in mind for prospective iStreamer buyers.

iStreamer Compatibility:

• iPod touch (1st, 2nd, 3rd and 4th generation)
• iPod classic
• iPod nano (1st, 2nd, 3rd, 4th, 5th and 6th generation)
• iPhone
• iPhone 3G
• iPhone 3GS
• iPhone 4
• iPad
• iPad 3G


In general, I found the iStreamer offered smooth, neutral tonal balance with solid but not exaggerated bass, a good measure of midrange openness, and very smooth highs that seemed to be rolled off just a hair. For many listeners, these characteristics point toward a DAC that is eminently musical—never cold, brash, brittle-sounding, or analytical. The benefit, of course, is that the iStreamer lets users completely bypass the slightly raw, coarse-sounding sonics of Apple’s own DAC and analog audio electronics to step up to a whole different (and better) class of performance.

But the iStreamer’s signature characteristic is an uncanny quality of rock-solid stability, which manifests itself as a sonic sense of purity of timber and “locked-to-a-clock” rhythmic precision. Another benefit is a certain desirable quality of ease in the iStreamer’s presentation. I can’t say for sure, but I believe these positive qualities may very well be attributable to the HRT’s “jitter-free host mode interface.”


I put the iStreamer through several sets of comparisons tests, with outcomes as noted below.

iPod Classic with and without iStreamer

For this comparison I conducted three sets of tests, always using the same set of lossless, CD-resolution files stored on an iPod Classic. All listening was done through Ultimate Ears In-Ear Reference Monitors.

I began by listening to the iPod Classic connected directly to a pair of Ultimate Ears IERM's. Next, I used Moon Audio Silver Dragon line out dock (LOD) cable to connect the iPod Classic to an ALO Audio Rx Mk II portable headphone amplifier. Finally, I inserted the iStreamer in the signal path, connecting the iPod Classic to the iStreamer and then used the iStreamer’s analog outputs to drive the ALO headphone amp.

iPod Classic + High Quality Headphones: The iPod did a decent job with the Ultimate Ears ‘phones, which are reasonably easy to drive. Even so, I noted a few shortcomings. First, bass was not as deeply extended or well-controlled as I would have liked, mids were somewhat forward-sounding and a bit splashy, while fast-rising, high-energy treble transients had a subtly aggressive, “pingy” quality that inexperienced listeners might mistake for “detail,” but that wasn’t really right.

iPod Classic + Portable Headphone Amp + High Quality Headphones: The iPod Classic gave significantly better performance when used with a high quality LOD cable and portable amp, exhibiting improved bass performance and smoother, better balanced, and more open-sounding mids and highs. But, even with the help of the cable and amp, the iPod still showed slightly less extended bass than would be optimal, residual hints of midrange forwardness, and highs that—though greatly improved—still showed traces of splashiness and a subtle lack of focus.

iPod Classic + iStreamer DAC + Portable Headphone Amp + High Quality Headphones: Once the iStreamer was put into the signal path, this playback system took another step up in performance, showing even better tonal balance, improved bass pitch definition and solidity, mids that sounded at once smoother yet also more transparent, and an overall presentation that was noticeably more coherent and focused.

Playing the iPod Classic through a good LOD cable and headphone amp improves its sound quality significantly and offers a good portable solution. For desktop or other in-home applications, however, adding the iStreamer elevates sound quality further still, giving a significant jump in performance, making the modest iPod sound more like a high-end source component in the process.

iStreamer vs. Computer-based Desktop System

For this comparison I conducted two listening tests. I began by listening to lossless CD-resolution digital audio files from a Windows PC (running iTunes) connected via USB inputs to a NuForce Icon HDP, which is a combination USB DAC/headphone amplifier. Next, I changed out the digital front end of the system, playing the same lossless digital files through an iPod Classic that was connected to the iStreamer, with the iStreamer’s analog outputs driving the analog audio inputs of the NuForce Icon HDP amp. All listening was again done through Ultimate Ears In-Ear Reference Monitors.

Computer + NuForce Icon HDP DAC/Amp + High Quality Headphones: The PC/NuForce-based system sounded very clear, but offered somewhat lighter tonal balance than would have been ideal. Relative to typical non-PC-based systems, the PC/NuForce-driven system offer better midrange focus, exceptional transient detailing, extended highs, and overall stability and coherence comparable to the results achieved with the iStreamer in the system.

iPod Classic + iStreamer DAC+ NuForce Icon HDP Amp + High Quality Headphones: The iPod/iStreamer/ NuForce-based system offered slightly warmer and more full-bodied tonal balance than the PC-based system did, with superior bass weight, midrange focus that was good (though perhaps not quite up to the Icon’s level of performance), good transient detailing and smooth highs, and with just a trace of treble rolloff.

Both the PC-based and iPod/iStreamer-based desktop systems offered better sound quality that could be achieved using just the analog outputs of an iPod as the “front end” of the system. Which digital source one prefers—the PC + NuForce DAC vs. the iPod Classic + iStreamer DAC—largely will be a matter of listening tastes. The PC + NuForce DAC combo will appeal to those who prize clarity, transient speed, and treble extension, though its sound might be too lightly balanced for some tastes. The iPod Classic + iStreamer DAC combo, on the other hand, will appeal to those who favor a smoother, more relaxed, and more organic sound, while giving up only a subtle degree of apparent transient speed and definition. The iPod + iStreamer combo’s superior bass performance and warmer tonal balance will, I think, strike many listeners as offering the more forgiving and “musical” sound overall.

iStreamer vs. High-End Disk Player

For this comparison I conducted two tests. First, I played a group of Redbook CDs through a very high quality, high-end Musical Fidelity kW SACD/CD player, which in turn was connected to a hand-made Burson Audio AB-160 vacuum tube buffer and HA-160 headphone amplifier. Next, I played lossless CD-resolution digital audio files ripped from those same CDs through the iPod Classic/iStreamer DAC combo, which also was connected to the Burson Audio tube buffer and amp. All listening was done through a pair of HiFiMAN HE-5LE planar magnetic headphones.

High-End Disk Player, Headphone Amp and Headphones: Not too surprisingly, the multi-thousand dollar Musical Fidelity kW SACD/CD player delivered higher performance in an absolute sense than the iPod/iStreamer combination did. The big Musical Fidelity player’s sonic superiority manifested itself in several ways; the kW player offered a heightened sense of transparency and openness from top to bottom, greater treble clarity and extension, a subtle quality of harmonic richness and self-consistency, and a quality of dynamic energy and “jump”—particularly on syncopated pop music. But with all of this said, the fact is that the iPod/iStreamer combo came closer (much closer) to the sound quality of the benchmark player than it had any right to for the money.

iPod Classic, iStreamer DAC, High-End Headphone Amp and Headphones: What the superb and very revealing Burson Audio electronics and HiFiMAN headphones showed was that the little iStreamer is very rich in detail in its own right, and that it is also sounds unfailingly smooth—even on difficult, high-energy treble transients that would give most other budget-priced DACs fits. The iStreamer produces bass that is taut, powerful, and well-defined, while its midrange has a certain natural warmth and seductive smoothness, augmented by the HRT DAC’s signature coherency and focus.

When push comes to shove, the iStreamer can be surpassed by expensive top-tier gear, but that in no way undercuts the fact that this superb little DAC plays way above its pay grade, so to speak.

One revealing disk that showcases several of the iStreamer’s strengths is Mary-Chapin Carptenter’s Come On, Come On [Columbia]. Put on “I Am a Town” from that album and listen carefully to the timbre and presentation of the acoustic bass that accompanies Ms. Carpenter's voice throughout the song, noting the instrument’s rich, deep, vibrant lower-midrange voice. Some DACs make the bass sound overly light and lacking in weight (more like a cello or viola), but the iStreamer gets the tonality of the bass exactly right, perfectly capturing those delicious amber midrange tonal colors that—to my way of thinking—really define upper register of the bass.

Similarly, on the title track of Come On, Come On, listen to the textures and high harmonics of Ms. Carpenter’s voice as she half sings/half whispers the song’s signature lines during the chorus, “Come on, come on/It’s getting late now/Come on, come on/Take my hand/Come on, come on/You just have to whisper/Come on, come/I will understand.” Through the iStreamer you’ll enjoy the delicate and breathy qualities in the singer’s voice as well as its higher harmonics, but without any excess treble sizzle or artificial high-frequency "pyrotechnics," and as a result you can’t help but be drawn into a more intimate connection with the singer’s carefully crafted vocal lines. What makes the iStreamer so special and so pleasing is that it sounds as if it could and perhaps should cost more, yet it is also a DAC that in a sense sounds “comfortable in its own skin”—as if it is rightly confident of its strengths and thus feels no need to convince listeners it is something it’s not.

While multi-thousand dollar disk players can and at times do outperform the iStreamer (as is only right given the huge price differentials involved), the fact is that the iPod/iStreamer combo generally holds its own, always giving you more than your money’s worth in a musical sense.


Consider this product if: you want an affordable, easy-to-use, high-quality DAC geared specifically for use with Apple devices, and that gives you a high-performance vehicle for connecting Apple portable players to desktop audio, home stereo, or home-theater systems. In particular, consider the iStreamer if you like the idea of trying a DAC that provides a jitter-free host mode interface to Apple portables.

Look further if: you were hoping for a portable device and/or for a digital Apple dock suitable for use with third-party outboard DACs. The iStreamer offers a lot of performance for the money, but it doesn’t support those two functions.

Ratings (relative to comparably-priced DACs):

•Design & Features: 9
•Tonal Balance: 9.5
•Timbral Purity: 9.5
•Detail & Resolution: 9
•Imaging/Soundstaging: 10
•Dynamics: 9
•Value: 10 (the iStreamer is really the only Apple-specific DAC in this price range, and one that offers a host mode interface, to boot)

Summing Up: HRT’s iStreamer provides an easy-to-use and extremely good-sounding means of connecting Apple’s modern portable audio devices to high-end desktop, home stereo, or home theater systems. The iStreamer provides significantly better sound quality than any analog iPod dock can hope to match, while its host mode interface gives the iStreamer a coherent, well-focused sound that enables it to play with the big boys—delivering credible high-end sound from Apple’s popular portable audio devices.


High Resolution Technologies iStreamer DAC
Accessories: Power supply, power supply cable, Apple-compatible dock/USB cable, RCA interconnect cables
DAC: 16-bit, with support for 32 kHz, 44.1 kHz, and 48 kHz data rates
Digital Input: USB
Transfer Protocol: Host Mode (master)
Analog Output: Stereo analog audio (RCA jacks)
Full Scale Output: 2.25V RMS
Frequency Response: 20 Hz- 20 kHz, 0dB/-.4dB
Noise Floor (DC -> 30 kHz): 28uV
Signal/Noise Ratio: 98dB
THD + Noise (1 kHz FS 44.1 kS/s): .002%
Dimensions (H x W x D): .875” x 2.3” x 4.6”?
Weight: Not specified?
Price: $199.95

High Resolution Technologies
(323) 967-7447

Elite Audio Video Distribution
(800) 457-2577 Ex. 22

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