HoloAudio Spring "Kitsuné Tuned Edition" Level 3 D/A processor Measurements

Sidebar 3: Measurements

I measured the HoloAudio Spring DAC "Kitsuné Tuned Edition" Level 3 with my Audio Precision SYS2722 system (see the January 2008 "As We See It"), using both the Audio Precision's optical and electrical digital outputs and USB data sourced from my MacBook Pro running on battery power with Pure Music 3.0 playing DSD and AIFF test-tone files. Apple's USB Prober utility identified the Holo Spring as "xCORE USB Audio 2.0" from "XMOS," its serial number as "0 (none)," and confirmed that its USB port operated in the optimal isochronous asynchronous mode. Apple's AudioMIDI utility revealed that, via USB, the Spring accepted 24-bit integer data. Its optical, coaxial, and AES/EBU inputs accepted datastreams with sample rates up to 192kHz, and its USB input accepted streams sampled up to 768kHz!

The maximum output level at 1kHz in the Spring's NOS, OS, and OS PCM modes was 4.95V from the balanced outputs and 2.475V from the unbalanced outputs, the latter 1.85dB higher than the CD standard's 2V. However, the output levels dropped by 6dB when I switched the Spring to DSD mode. All outputs preserved absolute polarity. (The XLR jacks are wired with pin 2 hot.) The unbalanced output impedance was close to the specified 200 ohms, at 218 ohms across the audioband. The balanced output impedance was twice that value, as expected.

The reconstruction filter's impulse response in NOS mode was a perfect pulse (fig.1; ignore the tiny amounts of pre- and post-ringing, which are due to the SYS2722's anti-aliasing filter, operating at a sample rate of 200kHz). When I set the DAC to OS mode with oversampling engaged (the OS PCM and DSD modes behaved identically), the impulse response indicated that the reconstruction filter is a conventional, linear-phase, FIR type (fig.2).


Fig.1 HoloAudio Spring, NOS mode, impulse response (one sample at 0dBFS, 44.1kHz sampling, 4ms time window).


Fig.2 HoloAudio Spring, OS mode, impulse response (one sample at 0dBFS, 44.1kHz sampling, 4ms time window).

In NOS mode there is no digital reconstruction filter, and with white noise sampled at 44.1kHz (fig.3, magenta and red traces, footnote 1) there is a slow rolloff above the audioband, disturbed by nulls at 44.1 and 88.2kHz. Consequently, the aliased image of a full-scale 19.1kHz tone (cyan and blue traces) was hardly suppressed at all. With the Spring in OS and OS PCM modes, the filter rolled off rapidly above half the sampling frequency, and reached full stop-band suppression at 24kHz (fig.4, magenta and red traces). The image of a full-scale 19.1kHz tone (cyan and blue traces) is therefore suppressed by >100dB. The distortion harmonics of this tone are very low in level; the third harmonic is the highest in level, at –84dB (0.006%). In DSD mode (fig.5, magenta and red traces) the rolloff above 20kHz is also very steep, but the expected rise in the ultrasonic noise floor due to the DSD encoding is evident.


Fig.3 HoloAudio Spring, NOS, wideband spectrum of white noise at –4dBFS (left channel red, right magenta) and 19.1kHz tone at 0dBFS (left blue, right cyan), with data sampled at 44.1kHz (20dB/vertical div.).


Fig.4 HoloAudio Spring, OS PCM, wideband spectrum of white noise at –4dBFS (left channel red, right magenta) and 19.1kHz tone at 0dBFS (left blue, right cyan), with data sampled at 44.1kHz (20dB/vertical div.).


Fig.5 HoloAudio Spring, DSD, wideband spectrum of white noise at –4dBFS (left channel red, right magenta) and 19.1kHz tone at 0dBFS (left blue, right cyan), with data sampled at 44.1kHz (20dB/vertical div.).

In NOS mode a gentle rolloff begins in the mid-treble with PCM data sampled at 44.1kHz, but starts a little higher in frequency with data at 96 and 192kHz (fig.6). The surprise, however, is that in DSD mode the Holo Spring's frequency response extends no higher with 192kHz-sampled PCM data than it does with 44.1kHz data. This can be seen in fig.7, which compares the responses with 192kHz PCM data in NOS, OS, and OS PCM modes with that in DSD mode. The last rolls off sharply above 19kHz.


Fig.6 HoloAudio Spring, NOS, frequency response at –12dBFS into 100k ohms with data sampled at: 44.1kHz (left channel green, right gray), 96kHz (left cyan, right magenta), 192kHz (left blue, right red) (1dB/vertical div.).


Fig.7 HoloAudio Spring, frequency response at –12dBFS into 100k ohms with data sampled at 192kHz in mode: NOS (left channel blue, right red), OS (left cyan, right magenta), OS PCM (left yellow, right gray), DSD (left green, right blue) (1dB/vertical div.).

Channel separation was superb, at >125dB in both directions below 1kHz, and the Spring's noise floor was both very low in level and commendably free from power-supply–related artifacts. A relevant issue with resistor-ladder DACs is the linearity error: Will a digital signal at, for example, –80dBFS be reproduced at the outputs by an analog signal the same 80dB down from full level? However, the Spring performed well in this respect (fig.8). When I examined linearity, the error was negligible down to –60dBFS, and remained below 1dB down to 90dBFS. Increasing the bit depth from 16 to 24 with a dithered 1kHz tone at –90dBFS (fig.9) dropped the noise floor by 30dB. However, the many distortion harmonics visible in the 24-bit signal suggests something is not optimal in the Spring's handling of low-level data with this bit depth. Perhaps the LSBs are being truncated. With undithered data representing a tone at exactly –90.31dBFS (fig.10), the three DC voltage levels described by the data were well resolved. With undithered 24-bit data, the result was a clean sinewave (fig.11).


Fig.8 HoloAudio Spring, NOS, 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.).


Fig.9 HoloAudio Spring, linearity error (red, 5dB/vertical div.) and output level vsdBFS (blue, 10dB/vertical div.), form 0dBFS to –120dBFS, 24-bit data.


Fig.10 HoloAudio Spring, OS PCM, waveform of undithered 1kHz sinewave at –90.31dBFS, 16-bit TosLink data (left channel blue, right red).


Fig.11 HoloAudio Spring, OS PCM, waveform of undithered 1kHz sinewave at –90.31dBFS, 24-bit TosLink data (left channel blue, right red).

As suggested by figs. 4–5, harmonic distortion was very low. Even at maximum output into the punishingly low 600 ohm load, the distortion harmonics all lay at or below –114dB (0.0002%), though many higher-order harmonics are visible (fig.12). In NOS mode, the poor ultrasonic rejection gave rise to a multitude of aliased images with a full-scale mix of 19 and 20kHz tones (fig.13), and reducing the signal level by up to 10dB produced no change in the number of images. Fortunately, music rarely has significant energy toward the top of the audioband, and switching to the OS and OS PCM modes revealed that actual intermodulation distortion was very low (fig.14). It was even lower in DSD mode (fig.15), but that might be connected with the Spring's lower maximum output level in that mode.


Fig.12 HoloAudio Spring, spectrum of 50Hz sinewave, DC–1kHz, at 0dBFS into 600 ohms (left channel blue, right red; linear frequency scale).


Fig.13 HoloAudio Spring, NOS, HF intermodulation spectrum, DC–30kHz, 19+20kHz at 0dBFS into 600 ohms, 44.1kHz data (left channel blue, right red; linear frequency scale).


Fig.14 HoloAudio Spring, OS, HF intermodulation spectrum, DC–30kHz, 19+20kHz at 0dBFS into 600 ohms, 44.1kHz data (left channel blue, right red; linear frequency scale).


Fig.15 HoloAudio Spring, DSD, HF intermodulation spectrum, DC–30kHz, 19+20kHz at 0dBFS into 600 ohms, 44.1kHz data (left channel blue, right red; linear frequency scale).

When I tested the Spring in NOS mode for its rejection of word-clock jitter, using undithered 16-bit J-Test data fed to the AES/EBU input, most of the odd-order harmonics of the low-frequency, LSB-level squarewave were at the correct levels, as shown by the sloping green line in fig.16. However, those harmonics closest to the spectral spike that represents the high-level tone at one-quarter the sample rate were exaggerated in level. This behavior was identical when I repeated the test using the optical, coaxial, and USB inputs, and when I used 24-bit J-Test data, it appeared that the Spring in NOS mode introduced sidebands spaced at ±229.16Hz and at odd-order multiples of that frequency (fig.17). Switching to any of the oversampling modes gave a much cleaner spectrum with 24-bit data in the right channel (fig.18 red trace), but there were still problems in the left channel (blue).


Fig.16 HoloAudio Spring, NOS, high-resolution jitter spectrum of analog output signal, 11.025kHz at –6dBFS, sampled at 44.1kHz with LSB toggled at 229Hz: 16-bit AES/EBU data (left channel blue, right red). Center frequency of trace, 11.025kHz; frequency range, ±3.5kHz.


Fig.17 HoloAudio Spring, NOS, high-resolution jitter spectrum of analog output signal, 11.025kHz at –6dBFS, sampled at 44.1kHz with LSB toggled at 229Hz: 24-bit AES/EBU data (left channel blue, right red). Center frequency of trace, 11.025kHz; frequency range, ±3.5kHz.


Fig.18 HoloAudio Spring, OS, high-resolution jitter spectrum of analog output signal, 11.025kHz at –6dBFS, sampled at 44.1kHz with LSB toggled at 229Hz: 24-bit USB data (left channel blue, right red). Center frequency of trace, 11.025kHz; frequency range, ±3.5kHz.

HoloAudio's Spring DAC offers mainly excellent measured performance. While some more questionable aspects of that performance are related to the NOS mode's lack of a conventional digital filter, the oversampling modes behave much better on those specific tests. But there's something funky in the Spring's rejection of word-clock jitter, particularly in the left channel.—John Atkinson

Footnote 1: My thanks for Jürgen Reis of MBL for suggesting this test to me.

tonykaz's picture

It's nearly 2020 now and I remember saying "only just begun" since the 1950s with an LP recording of a Tchaikovsky Violin Concerto ( in Mono ) after living with 78s.

Sheffield Labs brought another "only just begun" , LINN LP-12 brought another, Electrocomaniet brought another, Brisson MIT speaker cable brought another, Koetsu brought another, Gordon Rankin another, Ken Smith of PS Audio brought another.

We've lived thru a lifetime of "only just beguns" , haven't we ?

I'm ready for more of em, they're exciting.

Of course R2R isn't new or respected by Audio Professionals ( for the most part ). Still, I anticipate R2R architecture will be in the mother boards of many smart phones, the Phone people have "only just begun" !

An Audiophile grade R2R DAC for well under MSB price points is both wonderful that it exists and scary that it's coming from the Uttr side of the Voild. for gods sake

Tony in Michigan

ps. can someone ( without Orange hair ) take me back to 1910's Isolationist practices?

spacehound's picture

If I didn't already have a considerably more expensive (but not necessarily better), DAC I would buy one.

I purchased my last 'regular chip' DAC a long time ago and no longer use it. It's R2R, dCS (discrete components) or Chord (FPGA) for me, they are so much better.

brw's picture

This is the best DAC review I have ever read. Especially the comparisons with Yggdrasil (which I’ve long been tempted to buy). Thoughtful impressions, differences discerned with specific tracks, tongue-in-cheek humor (“LSD vs. DSD”). Super-helpful observations that will undoubtedly influence, if not motivate my next purchase. This is why I read Stereophile. Well done, Herb.

Herb Reichert's picture

this review was the most difficult review I've written so far. To effectively characterize the Holo Spring while putting its low price and original engineering into the proper historical perspective was a real challenge . . . . thanks again - I am glad you enjoyed it

Greg121986's picture

What digital input on the Spring did you use? Sorry if I may have missed this detail from the article. I've owned the Spring KTE L3 for awhile, and it is customary to use its I2S input with a digital-digital converter. This method yields substantially better sound than the USB input alone. Unfortunately the USB input on the Spring is not as much of a high quality piece as the rest of the DAC. I have heard of users being satisfied with the AES/EBU balanced input as well but I have no personal experience with this. For I2S I use the Singxer SU-1 DDC which is pretty much the go-to piece of equipment for the Spring. The improvement to the Spring when using its I2S input is corroborated many times over by other owners as well.

Herb Reichert's picture

the I2S + Singxer and the USB with an AudioQuest Cinnamon cable. I cut the DDC out of this story because the Singxer is a seperate product not yet reviewed in Steriophile.

ednazarko's picture

Seems to me from reviews that R2R has a lot of real advantages over the most widespread approach to DACs today.

So why did R2R phase out? Does it not hold up as well as a fully chip system? Is it trickier to get right?

Curious to hear this bit of audiophile history...

DriverTube's picture

I enjoyed your review of the Holo Spring DAC (and your column in general)! I have been happily using the Holo Spring (Level 1) for about 7 months and it really has had an impact in terms of my ability to enjoy listening to digital music. I have had significantly more expensive DACs and while they always sounded very impressive in many ways, there was a strange disconnect between their sonic abilities and their ability to let me enjoy my music. Not so with the Holo Spring. One thing that you might try, early versions (pre 2018?) of the Holo Spring used a U208 XMOS USB module while later versions switched to the newer, improved UX208 XMOS USB module. Jeff at Kitsune can supply the newer USB board which is a 2-bolt, drop-in replacement swap. At first, I thought the UX208 provided a VERY slight increase in transparency and perceived detail. However, as I have become more familiar with it, I think it is a real if subtle improvement. Maybe a good option for anyone wanting a simple USB connection without extra boxes/I2S converters? Looking forward to hearing from you in the future about more fun stuff!

georgehifi's picture

Because it didn't do DSD and the main reason it was so expensive to manufacture, because of the laser trimming of all the R2R resistors. Up to 50 x the cost of Delta Sigma dac chips.

The only ones left are not made for the audio industry but military, that the Schiit Yaggy uses.

So what's happening to the manufacturers that still believe R2R multibit is still the better way, is their "doing their own discrete (not chip) version of it", and that's very hard to do in discrete components with all the matching of those resistors. Here are a list that are now doing R2R Multibit, and it's growing.

Up to $3k: Border Patrol, Monarchy, Denafrips, Audio-gd, MHDT, Holo, Soeskris, Metrum, Schiit

$5-$15K: Audio Note, MSB, Metrum, Computer Audio Design, Aqua, LessLoss, Totaldac, Lampizator

$15K+: CH Precision, Aries Cerat, Light Harmonic, Audio Note, MSB, Totaldac, Lampizator

**Special mention to MSB, Monarchy and Audio Note, who never gave up R2R. Even after the takeover of delta-sigma.

Cheers George

dce22's picture

Or you can bypass that junk and get the best R2R DAC

LavryGold DA924

The R2R DAC that is used in mastering studios to transfer the music from the PC to Analog compressors and EQ's then to PC again with LavryGold AD122-96 that is R2R based ADC

This Lavry DAC to ADC chain is probably on people's favorite recording without they even know it


SNI's picture

That would probably be one of the reasons for R2R DAC chips deminish, but there are a few more reasons.
The most important is, that it is possible to obtain somewhat better performance with sigma delta DACs, and in many cases the implementation is also simpler.
Of the six OEM (Now five) about half of them early chose the sigma delta technology over the R2R principle.
Philips was probably the company, that drove the devellopment fastest and furthest of all. They later sold their patents to Crystal Semi, which now is Cirrus Logic.
Anyways R2R DACs are always I out DACs which needs an ekstra step for I/V convertion. This step is pretty critical, and complicates the implementation of the R2R chips.
Sigma Delta DACs with Switced Capacitor Outputstages and filtering dosn´t need I/V conversion, hence the implementation is both simpler and cheaper. This also can lead to better sound quality in the end.
Especially Cirrus Logic and AKM have adopted this principle, and today their DAC chips are absolutely top notch.

vsrwiz's picture

The combination of Holo Spring Wild edtion DAC, UIP, SU1 with Xsymphony USB cable created a magic to ears. The music had a relaxed, natural sound that was never stressful to listen to, it was like more and more analogue and lacked any trace of the digital grit which i have heard from other company DACs. Listening to music over long stretches of time was comfortable and inviting.

My favorite “Girl from Ipanema" (DSD) and Spanish Harlem(24-bit/96kHz Flac) sounded very realistic, with well-fleshed-out harmonic structural reproduction of the instruments (or reproductions thereof).
The combination of Spring Wild Modded, UIP, SU1 threw a wide, dense sound stage with instruments distributed across the space between the speakers. The deep bass on this recording descends to between 20 and 30Hz, and was reproduced with deep extension and powerful impact on tight bass. I was really impressed by the the combination handling of both micro and macro dynamics, which provided a sense of liveliness and energy.

While listening to the Jorge Bolet "Liszt Piano Works", I could always distinguish the percussion instruments clattering in the background (through some other instruments, they merge into a background mush). Leading-edge lows, mids & highs was really well defined: not peaky or edgy, just sharp and clear.

By Connectiing Xsymphony AES Cable, the combination of Spring Wild Modded, UIP and SU1 was more better, it was really very musical and good, even before the burn-in time and reproduced with great realism and sharp transients -- not at all peaky, just natural and the bass was so deep and powerful.

Stings's picture

Has anyone listened to both the Holo Spring and the ifi Pro IDSD dac? I am debating whether to buy the Holo Spring or ifi Pro iDSD. I like the fact that the ifi pro iDSD has a Ethernet and upsamples to dsd1024 but it doesnt have a i2s connector.
Which DAC is better realistic imagery?


Herb Reichert's picture

Reviewed both and found them both to play like a $20K DAC. The sound character of each is very different though. To my subjective view, the Holo Spring is the most natural and least (digitally) affected but the iDSD delivers a force of 'energy' and transparency very much like the Mytek Manhattan II DAC. I could live happily with either.

Thanks for reading my prattles.


highdesertdog's picture


Thank you for a thoughtful and useful comparison review. Have you heard another R2R DAC, the Mojo Audio Mystique v3?

DetroitVinylRob's picture

Herb, you guys are the best, truly!

Thoroughly enjoyed the read, and the observations by both you and Art. I trust your ears. Thank you. I am perhaps less experienced with DSD than some other things as well... Yet this Holo Audio Spring Kitsuné Tuned Edition Level 3 sounds like a real digital sweetheart. It may just prove to be my entry to home streaming.

By the way, you and I sat next to one another a year ago at RMAF while listening to Joyce DiDonato performing La Vestale, act.2 Se Fino Al Cielo Ascendere on Raidho loudspeakers. I shared the meta data with you off the Shazam app on my iPhone.

Thank again, Rob [|;^)>