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Srajan Ebaen
Financial Interests: click here
Main Source: Ancient Audio Lektor Prime, 1TB iMac (AIFF) via FireWire 800 into Weiss DAC2
Desktop Source: MacBook Pro (WAV), iPod Classic 160GB (AIFF), Sieben Technology dock
Main Preamp/Integrated: Esoteric C-03 (transistor), ModWright DM 36.5 (valves)
Desktop Integrated: Peachtree Audio iDecco with USB, NuForce HDP [on review]
Amplifier: FirstWatt F5
Speakers: ASI Tango R, Dayens Tizo [on review]
Cables: Complete loom of ASI Liveline, ALO Audio & Entreq USB cables
Stands: 2 x ASI HeartSong 3-tier, 2 x ASI HeartSong amp stand
Powerline conditioning: 1 x Walker Audio Velocitor S, 1 x Furutech RTP-6
Sundry accessories: Furutech RD-2 CD demagnetizer; Nanotech Nespa Pro; extensive use of Acoustic System Resonators, noise filters and phase inverters, Advanced Acoustics Orbis Wall & Corner units
Room size: The sound platform is 3 x 4.5m with a 2-story slanted ceiling above; four steps below continue into an 8m long combined open kitchen, dining room and office, an area which widens to 5.2m with a 2.8m ceiling; the sound platform space is open to a 2nd story landing and, via spiral stair case, to a 3rd-floor studio; concrete floor, concrete and brick walls from a converted barn with no parallel walls nor perfect right angles; short-wall setup with speaker backs facing the 8-meter expanse and 2nd-story landing.
Review Component Retail: $499.95

By combining unexpected performance with entry-level pricing, Kevin Halverson's previous two iterations of the High Resolution Technologies Streamers—full USB to analog converters running off USB's 5V power—became a runaway success. They weren't marketed as state of the art but bridge products for the younger PC audio nation. The Streamers garnered very positive even enthusiastic press. Awards included a TAS Golden Ear and our Realsization. As its name implies, the fully balanced MS Pro with its 4.5V TiniQ outputs ("if you produce, mix, master or listen to music in a professional environment") foremost aims at the professional market. After the success of the Streamer and Streamer+ models now both in II iteration, numerous cable makers like Cardas and Entreq anticipated significant home use for the Pro. They've authored custom TiniQ-to-XLR or RCA cables and adaptors. On Kevin's latest Streamer, hifi buffs can thus go prosumer with either custom cables or their very own.*

* Having been solicited by Scot Markwell of Elite Audio Video, HRT's US/Canadian distributor, I accepted his offer for two short lengths of custom TiniQ Furutech cable loaners. These would accommodate both my Peachtree Audio iDecco integrated on RCA and Esoteric's C-03 preamp on XLR. I wanted to conduct comparisons between the Pro Streamer on my MacBook versus the digital-direct iPod in the Peachtree Audio iDecco on the desk top; and between the Firewire 800 iMac/Weiss DAC2 combo in the big system and the iMac and Pro combo via USB cables by Entreq and ALO Audio.

The 24/96 MS Pro is currently the statement Streamer from High Resolution Technologies. A 24/192-enabled HD model will bow once "final development work is completed to make it work well with both Mac and PC. Some software 'tricks' are required that are being fine-tuned now. This model will also have an IEC as its power requirements exceed what is available from the USB buss." Scot Markwell added that "as for the Pro, there will likely always be a bit of  controversy as to how its power is derived but the Pro works comfortably in most installations. For folks who run a lot of  peripherals, we recommend an independently powered USB hub." Electrical specifications include a 200Ω output impedance, an A-weighted noise floor of 8μV RMS with a S/N ratio of 115dB and a digital input to analog output isolation of >20MΩ. Physical dimensions are quite tiny at 2.1 x 5.6 x 1.2" WxDxH.

Kevin Halverson commented on the presumption that the problem with a host computer as power source is somehow related to having to clean up the 5V supply: "That's incorrect. Cleaning up nasty raw power supplies is a fairly trivial task. It can be accomplished by methods known to anyone skilled in the art of power supply design. There are a number of ways to accomplish this. Clean power is neither the only problem associated with a computer as audio source nor even the most important. Even if one had a completely independent power supply (battery or mains supplied), computer contamination remains. The power isn't the problem. The common ground is. Here all the noise gets conducted. The D+ and D- data pair of USB must be accompanied by a ground connection. It is this ground connection which conducts all the computer-generated nasties right into the analog audio ground. Unless some extraordinary efforts are made to isolate the computer and audio sides, all power supply clean-up efforts are wasted. The ground of the USB link maintains a constant connection of the computer with the rest of the audio system. 

"In the case of the Streamers, we provide complete isolation between the computer and analog sides. Not only do we regenerate the power (thereby breaking the common ground), we do the same with all the data moving between the two halves. This allows us to draw power from the host computer. Because we are completely isolated, the fact that we're connected to the computer has no impact on the performance of our product."

The previous Streamer+ had Stereophile's Art Dudley urge us to just buy it! HiFi+'s Alan Sircom chirped "...don’t underestimate the viral aspect of these Streamers. From personal experience, we found it difficult not to spread the word. Look at it this way; many of us know people who use laptops to serve their music these days. If you have one of these, you will put it in your pocket and take it over to them. They will, in turn, get one and do the same to their friends. And so on until you end up breaking Facebook. So you too can become the Avon Lady of hi-fi."

Also reviewed by us, the Streamer+ employed a switch-mode circuit to create ±5V power supply rails; a PCM2706 USB receiver chip: a 24-bit PCM1794 for actual D/A conversion; NE5534 I/V converters; and BB OPA2132 op-amp output drivers. How did the Pro's architecture differ now?

Kevin Halverson: "The new Streamer II+ and Pro differ in the post DAC area. The implementation of the I/V stage as well as the reconstruction filters and a differential I/O amplifier in a balanced topology are what distinguish the Pro from the Streamer II and II+. The older Streamer+ was a differential design up until the last stage, the Streamer Pro is differential from the DAC to the analog output connectors.

"As do all current Music Streamer models, the Pro utilizes asynchronous transfer protocol. It also supports adaptive synchronous transfers for very old PCs which do not support asynchronous USB. All current Streamer models including the Pro use native Audio Class 1.0 drivers which are present in all modern OS. With any modern computer, the Streamer II, II+ and Pro work in asynchronous mode at all times. For over a decade now, asynchronous transfer has been part of the audio specifications though until recently, it has only been implemented in professional products.  All current HRT models support this capability.

"We chose the TAS1020B for our USB transceiver front end for all current Streamer models. This Texas Instruments part contains a general purpose micro section. That's where our own firmware/code is utilized. 

"Our implementation was generated completely in house and not licensed from elsewhere. Our code is fully class compliant. Unlike any firmware from other manufacturers, ours includes a number of extremely sophisticated routines for error handling. Soon we will be releasing a firmware upgrade and desktop applet to allow the end user configuration options for the mode/s of operation [the screen captures below show the setup options]. Relative to Gordon Rankin's statement that the TAS1020B is "programmable to rates up to 24/96", we have successfully transported data at rates near 176.4kS/S with this device. Alas its PHY is limited to USB 1.1FS (Full Speed) which makes it less than an ideal choice for triple speed (or higher) audio applications. Our soon-to-be-released Music Streamer HD will initially support audio data rates of up to 192kS/s but with a planned future firmware upgrade would support up to 384kS/s.

"My conjecture as to why, unlike in professional audio, asynchronous USB converters for consumer applications are still far from the norm is that one currently needs to develop proprietary firmware - or take the shortcut which some have and license it from others. The latter was unacceptable. I'd not want a situation where someone else had control over the behavior of one of my products. With someone else's code, we could not have developed the tight hardware integration we have." Budget-conscious readers should be pleased to know that even the $149.95 HRT Streamer II benefits from the same low-jitter USB transfer protocol as the rather more expensive asynchronous USB DACs from Ayre, dCS and Wavelength Audio. For measured verification that async mode does indeed lower jitter over adaptive mode transfer, refer to John Atkinson's relevant Stereophile measurements.

On audiophile geekery about further 'post DAC' details for the Pro, Kevin was refreshingly plain: "I never really liked the laundry list parts mentions that seem so prevalent. If we can focus on the things that actually matter, all the better by me. My mantra has always been that the three most important things in any audio design are topology, topology, topology. I am so not about pedigree parts. I have often claimed that even if one were limited to crappy components, if one developed the right topology, one could still have a great performing product."