HRT Music Streamer HD USB D/A processor Measurements

Sidebar 3: Measurements

My testing of the HRT Music Streamer HD was primarily performed with Stereophile's loan sample of the top-of-the-line Audio Precision SYS2722 system (see and the January 2008 "As We See It"), with some tests performed on my vintage Audio precision System One. The sources for the tests were WAV and AIFF files played from my MacBook Pro running BIAS Peak Pro and connected to the HRT with the Music Streamer set to USB2.0. I checked that the sample rate and bit depth were correctly set for each file with the Audio-MIDI setup utility. Bit depth was set to "24-bit Integer" for all tests and I didn't see any way to change it.

The USB Prober utility identified the HRT as "Music Streamer HD 2.0," with a manufacturer ID string of " 2013 REV 1.0," operating in Isochronous asynchronous mode. Audio-MIDI, however, identified the HRT as "USB 2.0 Audio Out." The Music Streamer HD operated correctly with USB data sampled at all rates from 44.1 to 192kHz, including 88.2 and 176.4kHz.

The HRT's maximum output level at 1kHz was 4.77V from its balanced jacks, 2.38V from the unbalanced, the latter 1.53V higher than the CD standard's 2V RMS. Both outputs preserved absolute polarity (ie, were non-inverting), the XLR jacks being wired with pin 2 hot. The balanced output impedance was 99 ohms, the single-ended 50 ohms (both figures include 6' of interconnect).

The Music Streamer Pro's frequency response followed the same basic pattern at all sample rates: a gentle rolloff beginning at 10kHz, reaching –0.3dB at 20kHz, with then a sharp drop-off just before half the sample rate (fig.1). The channels were matched to within 0.1dB. Fig.2 shows the behavior of the HRT's reconstruction filter. The red trace is the FFT-derived spectrum of a full-scale 19.1kHz tone sampled at 44.1kHz. Though the second, third, and fifth harmonics can be seen, there is no trace of the primary image of the tone at 25kHz (44.1–19.1kHz). The blue trace was taken with 44.1kHz-sampled white noise at –4dBFS. It reveals that the reconstruction filter rolls off very rapidly above 21kHz, reaching –110dBFS by 23kHz. However, the rate of rolloff slows dramatically above that frequency, something I also saw in the first sample of the iFi iDAC, reviewed last month, though that product uses a different DAC and digital filter. The noise floor begins to rise above 50kHz, perhaps due to the noise-shaping used by the HRT's Burr-Brown DAC chip.


Fig.1 HRT Music Streamer HD, frequency response at –12dBFS into 100k ohms with data sampled at: 44.1kHz (left channel blue, right red), 96kHz (left cyan, right magenta), 192kHz (left green, right gray) (1dB/vertical div.).


Fig.2 HRT Music Streamer HD, wideband spectrum of white noise at –4dBFS (left channel blue, right magenta) and 19.1kHz tone at 0dBFS (left cyan, right red), with data sampled at 44.1kHz (20dB/vertical div.).

Channel separation (not shown) was excellent, at 125dB in the midband and still 115dB at 20kHz, and the Music Streamer HD was very quiet. If "HD" stands for "High Definition," then the Music Streamer HD earns its name. The top two traces in fig.3 were taken by sweeping a 1/3-octave bandpass filter from 20kHz down to 20Hz while the Music Streamer HD decoded 16-bit data representing a dithered 1kHz tone at –90dBFS. The traces peak at exactly –90dBFS, suggesting minimal linearity error, which was confirmed by additional testing (not shown). The top traces in fig.3 actually show the spectrum of the dither noise used to encode the signal, there being no harmonics or power-supply spuriae visible.


Fig.3 HRT Music Streamer HD, 1/3-octave spectrum with noise and spuriae of dithered 1kHz tone at –90dBFS with 16-bit data (top) and 24-bit data (middle), and at –120dBFS with 24-bit data (bottom) (right channel dashed).

With 24-bit data (fig.3, middle traces), the noise floor drops by up to 24dB, suggesting that the DAC has around 20-bit resolution—superb performance even when not taking into account the Music Streamer HD's price, and easily enough to resolve a 24-bit tone at –120dBFS (fig.3, bottom traces). Repeating the test with a modern FFT technique (fig.4), I had to increase the vertical scale to 160dB in order to uncover the 24-bit noise floor (blue and red traces). However, this does unmask some very low-level distortion harmonics.


Fig.4 HRT Music Streamer HD, spectrum with noise and spuriae of dithered 1kHz tone at –90dBFS with: 16-bit data (left channel cyan, right magenta), 24-bit data (left blue, right red) (20dB/vertical div.).

With its superb resolution and low noise, the Music Streamer HD's reproduction of an undithered 16-bit tone at exactly –90.31dBFS was perfect (fig.5): the waveform is superbly symmetrical about the time axis, the three DC voltage levels described by the data are readily resolved, and the Gibbs Phenomenon "ringing" on the tops and bottoms of the waveform is not obscured by noise. This ringing also indicates that the HRT's reconstruction filter is a conventional linear-phase type. With undithered 24-bit data, the result is an excellent sinewave (fig.6).


Fig.5 HRT Music Streamer HD, waveform of undithered 1kHz sinewave at –90.31dBFS, 16-bit data (left channel blue, right red).


Fig.6 HRT Music Streamer HD, waveform of undithered 1kHz sinewave at –90.31dBFS, 24-bit data (left channel blue, right red).

At low frequencies (fig.7), the distortion signature comprises a collection of harmonics that decrease with order, with the second harmonic the highest in level, at –100dB (0.001%). The picture changes at higher frequencies, however, with the third harmonic now the highest in level (fig.8), at –90dB (0.003%). And looking back at fig.2, the third harmonics of the 19.1kHz tone in that graph lie at –66dB (0.05%). So though the distortion is low at all frequencies—and, commendably, unaffected by reducing the loading to 600 ohms!—there appears to be a relationship between the distortion spectrum and the signal frequency. I have no idea if this will have any bearing on the HRT's sound quality.


Fig.7 HRT Music Streamer HD, spectrum of 50Hz sinewave, DC–1kHz, at 0dBFS into 100k ohms (left channel blue, right red; linear frequency scale).


Fig.8 HRT Music Streamer HD, spectrum of 1kHz sinewave, DC–10kHz, at 0dBFS into 100k ohms (left channel blue, right red; linear frequency scale).

When it came to intermodulation distortion, an equal mix of 19 and 20kHz tones sampled at 44.1kHz, with the waveform peaking at 0dBFS, has the same dirty-looking spectrum I found with the HRT Music Streamer Pro, which Jon Iverson reviewed in February 2011, and which uses the same PCM1794 DAC chip. Repeating the test with 96kHz-sampled data gave the spectrum shown in fig.9. The spectrum is significantly cleaner overall, in that the noise floor is no longer obscured by enharmonic products, but a large number of intermodulation products spaced at 1kHz are visible. Reducing the signal level by 6dB dropped the level of the intermodulation products in the midband considerably, but the components at 1, 18, and 21kHz were reduced only by the same 6dB as the stimulus. It is very unlikely for music to contain high-level tones at the top of the audioband, but perhaps this particular test signal reveals some mathematical limitations of the digital filter.


Fig.9 HRT Music Streamer HD, HF intermodulation spectrum, DC–30kHz, 19+20kHz at 0dBFS into 100k ohms, 96kHz data (left channel blue, right red; linear frequency scale).

An asynchronous USB connection should be free from jitter problems; the Music Streamer HD's reproduction of 16-bit/44.1kHz J-Test data is excellent (fig.10), there being no jitter-related sidebands visible around the 11.025kHz tone, and all the odd-order harmonics of the 229.6875Hz LSB-level squarewave lie at the correct levels. With 24-bit J-Test data there appeared a pair of sidebands of unknown origin, at ±150Hz and a level of –135dBFS (fig.11).


Fig.10 HRT Music Streamer HD, high-resolution jitter spectrum of analog output signal, 11.025kHz at –6dBFS, sampled at 44.1kHz with LSB toggled at 229Hz: 16-bit data via USB from MacBook Pro (left channel blue, right red). Center frequency of trace, 11.025kHz; frequency range, ±3.5kHz.


Fig.11 HRT Music Streamer HD, high-resolution jitter spectrum of analog output signal, 11.025kHz at –6dBFS, sampled at 44.1kHz with LSB toggled at 229Hz: 24-bit data via USB from MacBook Pro (left channel blue, right red). Center frequency of trace, 11.025kHz; frequency range, ±3.5kHz.

Overall, HRT's Music Streamer HD measures significantly better than the Music Streamer Pro. There is, however, still that peculiar behavior with high-level 19 and 20kHz tones to contend with. As for why AD ultimately preferred the sound of the Halide HD: Though the Halide has less measured resolution, it does use a slow-rolloff reconstruction filter, something that listeners do seem to like.—John Atkinson

High Resolution Technologies, LLC
1027 N. Orange Drive
Los Angeles, CA 90038
(323) 967-7447

allhifi's picture

By sheer luck/curioisity, last year (2019) I found/purchaed a HRT III (DAC) that the seller packaged with a 1m length of AQ 'Cinnamon' USB cable. Price $75.00 CAD -for both, shipped !

Feeding the HRT a signal from a Pi 3B+ (running Volumio software) via Straightwire basic USB or XLO UltraPLUS USB cable resulted in absolutely brilliant SQ -via Interner Radio (128-320 Kb/s) 'streams' !

Having five other USB Sources/Streamers/DAC's (two direct Ethernet connection; CA 851N, NP-30) the remaining DAC's fed by Pi/Volumio all on various Internet Radio stations, switching between any of them resulted in very impressive SQ; far more engaging (open, layered, dynmaic, clean/clear than the majority of my experience with CDP's/DAC's -running full 16/44 (1,411 Kb/s) data rates !

Yeah, I'm late to the party,but are you kidding me ! Digital never sounded so consistently good/engaging.

Last week, a HRT 'MS-II' became available (for the same $75.00 CAD -arrghh!) and I connected it from the recently departed late-model Schitt 'BitFrost' (G5 USB) - also a very nice USB DAC.

The first couple days powered proved nice enough. and then, after a few more days (24/7 operation) and on a current Internet Radio station streaming 192 kb/s -OMG ! ('Absolutely 70's POP Radio' if you must know -lol) Simply glorious wall-to-wall sound with all/any of the typically included, cliched audiophile adectives used to convey 'tone', definition, layering, dynamics, 'staging', speed, dimensionality, realism (sheer, "unfettered" lol enjoyment) the entire past 6-12 hours on this very lazy Saturday afternoon/evening.

This, from the HRT II !! (??)

So shocked/pleased, I thought it best to order HRT's vaunted 'HD' DAC, tested/ reviewed here.

As I look to the test-bench measurements, I see Atkinson "worried" about some 19/20 Khz noise artifacts -in an otherwise SUPERB performance measurement profile that would/does put many, many other Stereophile DAC's test-bench results to shame -and far more expensive elaborate designs at that.

It's rather striking that some designers know full well the enormous advantages of small form-factor/circuit-boards for the finest digital performance (think Halverson-HRT/Watts-Chord) while the majoity are just beginning to discover the considerable benefits of short (digital) signal and power paths.

This strikes me unusual. And unfortunate.

Next week, I hope to be receiving my recently ordered HRT 'HD' DAC. If it's anything like the MS II/and III, I'll be in for another remkable revelation.

Great stuff these HRT/Halverson DAC's.

Summarizing, the growing sophistication in compresion algorthms (along with some better/more serious radio stations with an eye-ear to SQ) makes for a thoroughly enjoyable, entertaining, and dare I say insightful 'listen'.

Who would have thought this, back in 1989 ? I vividly recall shuddering at the SQ on offer via CDP's/early DAC's at that time -and what the audiophile/Hi-Fi industry had collapsed into ? I was truly saddended, dismayed.
Personally, it took another fifteen years beore I took the 'Digital Plunge'
(circa 2003/4 -22 years after CD's reease) and another 12-15 years to bring us here today -brilliant sounding 'Streaming'/Internet Radio over basically telephone/cable lines !

I could not have ever imagined this would be possible. More/ or less critical listening to these 'sources' the past 3-4 years has solifified its reputation; capability/ability and sheer SQ sophistication/involvement.

Returning back to 1982 for a moment (with the help of my ATH-7 Electret Condenser 'Cans' -Audio Technica), I could not tolerate CD/CDP's for more than a few minutes -at most. I vividly recall the local Hi-Fi shop -and the sheer disppointing (glassy, grainy, flat-hard) SQ experienced. It was complete, total and utter 'drek'. And remained that way a decade later. But then ....

That, my friends, was 38-years ago -two generations/40 years ago !!! to bring us here -musically compelling/enjoyable 'Every-Day-Digital' what vinyl/analog so easily captured -and continues- to this day.

Forty years -give/take a few. Ouch.

Good things do indeed come to those who wait, and wait ...

peter jasz