Merging Hapi MkII multichannel digital processor Measurements

Sidebar 3: Measurements

KR was still working on his review at the time I was scheduled to measure the Merging Hapi MkII, so Independent Audio loaned me a different sample for the testing. This sample had the serial number H95861 and was running firmware version 1.5.1b55774. I followed the instructions in the quick-start guide to download and install both the Merging MTDiscovery app and the RAVENNA/AES67 Virtual Audio Device (VAD) driver on my MacBook Pro. After I connected the Hapi to my router, the app found and identified it and opened its local control webpage on my browser. This page allowed me to select the digital input—AES3 or S/PDIF—set the maximum output level, choose the reconstruction filter, adjust the volume (in accurate 0.5dB steps), and select other functions. All the functions can be operated with the front-panel push knob, but the webpage is easier to use.

I used my Audio Precision SYS2722 system for the measurements, repeating some of the tests with the higher-resolution Audio Precision APx555. My Hapi sample was fitted with the optional DA8P D/A module; this had the serial number DP85778 (Run 14). The multichannel balanced analog output is implemented with a female, Tascam-standard DB-25 jack. I borrowed a two-channel DB-25–XLR adapter cable from KR for the testing. The Hapi's AES3 digital input is implemented with another DB-25 jack. As I didn't have a compatible adapter cable, I used the optical S/PDIF input for the testing, repeating some of the measurements with AES67 network data sourced from Adobe Audition running on my laptop. (There were no differences.)

I used the local webpage to set the Hapi to automatically accept the sample rate of the incoming data. (The rate can also be set manually.) All the testing was performed with the volume control set to its maximum and the maximum gain set to +18dBu. With those settings, a 1kHz digital signal at 0dBFS resulted in an output level of 6.55V. Setting the maximum gain to +24dBu increased the level by 6dB, as expected. The headphone output on the front panel has a fixed maximum level, this measuring 1.266V with a 1kHz tone at 0dBFS. The Hapi preserved absolute polarity, ie, was noninverting, from both the balanced and headphone outputs. The balanced output impedance is specified as a low 90 ohms; I measured 87 ohms from 20Hz to 20kHz. The headphone output impedance was 20 ohms at all audio frequencies.


Fig.1 Merging Hapi MkII, Sharp filter, impulse response (one sample at 0dBFS, 44.1kHz sampling, 4ms time window).


Fig.2 Merging Hapi MkII, Slow filter, impulse response (one sample at 0dBFS, 44.1kHz sampling, 4ms time window).

The Hapi offers a choice of four reconstruction filters: Slow, Sharp, Apodizing, and Brickwall. The Sharp filter's impulse response with 44.1kHz data (fig.1) indicates that this is a conventional linear-phase type, with time-symmetrical ringing on either side of the single sample at 0dBFS. The Brickwall and the Apodizing filters' impulse responses were identical to the Sharp filter's. The Slow filter's impulse response (fig.2) shows that this is a very short linear-phase filter, with minimal ringing.


Fig.3 Merging Hapi MkII, Apodizing filter, 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 Merging Hapi MkII, Slow filter, 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.).

With 44.1kHz-sampled white noise, the Hapi's response with the Apodizing filter rolled off sharply above 20kHz (fig.3, red and magenta traces), reaching full stop-band attenuation at 22.05kHz, half the same rate, as indicated by the vertical green line in this graph. The aliased image at 25kHz of a full-scale tone at 19.1kHz (blue and cyan traces) is suppressed by 100dB, and the highest-level distortion harmonic is the third, at –83dB (0.004%). The Brickwall filter (not shown) behaved identically, other than having a much lower level of the third harmonic. The Sharp filter's output (not shown) reached full stop-band attenuation at 24kHz. The Slow filter's output was down by 3dB at 20kHz and, as expected, its ultrasonic rolloff was the slowest of the four filters (fig.4), with the aliased image at 25kHz suppressed by 28dB.


Fig.5 Merging Hapi MkII, Brickwall filter, frequency response at –12dBFS into 100k ohms with data sampled at: 44.1kHz (left channel green, right gray), 96kHz (left cyan, right magenta), and 192kHz (left blue, right red) (1dB/vertical div.).


Fig.6 Merging Hapi MkII, Slow Filter, frequency response at –12dBFS into 100k ohms with data sampled at: 44.1kHz (left channel green, right gray) and 192kHz (left blue, right red) (1dB/vertical div.).


Fig.7 Merging Hapi MkII, 24-bit data, spectrum, 10Hz–1kHz, with noise and spuriae of dithered, 1kHz tone at 0dBFS (left blue, right red; linear frequency scale) (20dB/vertical div.).

Figs.5 and 6 respectively show the Hapi's frequency response with the Brickwall and Slow filters in greater detail. The sample rates are 44.1kHz (green and gray traces), 96kHz (cyan, magenta traces), and 192kHz (blue, red traces). The Apodizing filter differed from the other filters in having some passband ripple. Channel separation (not shown) was an excellent 113dB in both directions at 1kHz and still 110dB at the top of the audioband. Fig.7 shows the Hapi's low-frequency noisefloor as it drove a full-scale 1kHz tone with the volume control set to its maximum of "0.0dB." The level of the random noise is very low, and no AC supply–related spuriae are present.


Fig.8 Merging Hapi MkII, 1kHz output level vs 24-bit data level in dBFS (blue, 20dB/vertical div.); linearity error (red, 1dB/vertical div.).


Fig.9 Merging Hapi MkII, spectrum with noise and spuriae of dithered 1kHz tone at –90dBFS with 24-bit data (left blue, right red) and 16-bit data (left cyan, right magenta) (20dB/vertical div.).


Fig.10 Merging Hapi MkII, waveform of undithered 1kHz sinewave at –90.31dBFS, 16-bit data (left channel blue, right red).


Fig.11 Merging Hapi MkII, waveform of undithered 1kHz sinewave at –90.31dBFS, 24-bit data (left channel blue, right red).

The red trace in fig.8 plots the error in the analog output level as a 24-bit, 1kHz digital tone stepped down from 0dBFS to –140dBFS. Even at the lowest level, the amplitude error is <1.5dB, which implies very high resolution. When the Hapi decoded dithered 16-bit data representing a 1kHz tone at –90dBFS (fig.9, cyan and magenta traces), the tone was reproduced at the correct level and the noisefloor is that of the LSB-level dither. With dithered 24-bit data (blue, red traces), the noisefloor dropped by 30dB, which suggests the Hapi's DAC module offers a superbly high resolution of 21 bits. With undithered 16-bit data representing a tone at exactly –90.31dBFS (fig.10), the three DC voltage levels described by the data were accurately reproduced. With undithered 24-bit data, the waveform was a clean sinewave, despite the very low signal level (fig.11).


Fig.12 Merging Hapi MkII, 24-bit data, spectrum of 1kHz sinewave, 10Hz–10kHz, at 0dBFS into 200k ohms (left channel blue, right red; linear frequency scale).

The second harmonic was the highest, at just –123dB or 0.00007% (fig.12), with the fifth harmonic slightly lower in level. This graph was taken with the Audio Precision APx555's input impedance set to the high 200k ohms. With the load impedance reduced to the punishing 600 ohms, the third harmonic was now higher in level than the second but still lay at a very low –119dB (0.00011%).


Fig.13 Merging Hapi MkII, Apodizing filter, 24-bit data, HF intermodulation spectrum, DC–30kHz, 19+20kHz at 0dBFS peak, sampled at 44.1kHz.


Fig.14 Merging Hapi MkII, Slow filter, 24-bit data, HF intermodulation spectrum, DC–30kHz, 19+20kHz at 0dBFS peak, sampled at 44.1kHz.

The Hapi's behavior with an equal mix of 19 and 20kHz tones with a peak level of 0dBFS depended on the reconstruction filter. With all the filters, the difference product at 1kHz was vanishingly low in level, at –136dB. With the Sharp and Brickwall filters (fig.13), the higher-order intermodulation products were also very low in level, at less than –120dB. As expected from fig.4, the levels of the aliased images of the two high-frequency tones were much higher with the Slow filter (fig.14), but actual intermodulation products were still very low, even into 600 ohms.


Fig.15 Merging Hapi MkII, high-resolution jitter spectrum of analog output signal, 11.025kHz at –6dBFS, sampled at 44.1kHz with LSB toggled at 229Hz: 16-bit TosLink data (left channel blue, right red). Center frequency of trace, 11.025kHz; frequency range, ±3.5kHz.

Fed with 16-bit Miller-Dunn J-Test data via TosLink, the Hapi featured superb jitter rejection. All the odd-order harmonics of the LSB-level, low-frequency squarewave lay at the correct levels, indicated by the sloping green line in fig.15, and there were no spurious tones present. With 24-bit J-Test data (not shown), the noisefloor was commendably clean.

With its superbly high resolution, vanishingly low levels of noise and distortion, and superb jitter rejection, Merging's Hapi MkII offers state-of-the-digital-art measured performance.—John Atkinson

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ARTICLE CONTENTS

COMMENTS
Auditor's picture

Kalman,

Very interesting review

This is perhaps a dumb question, but here it goes...

Do you know whether it's possible to connect an SACD transport or a universal player to the Merging processor? I'm thinking of transports or players that are still in production today.

The idea would be to have the possibility of playing the multichannel layer (in native DSD!) directly from SACDs without having to rip anything or buy downloaded files.

Thanks!

Kal Rubinson's picture

I have thought of one way. It involves adding an external box to accept the HDMI output from the Oppo and convert it to 4 AES/EBU (XLR) outputs. Such a box is one from AudioPraise (https://www.stereophile.com/content/audiopraise-vanitypro-hdmi-audio-extractor).

Another possibility is one of several devices from Meridian (even the old HD621) which are available (new or used) and which can easily be adapted to the task. However, I am not sure whether or not these will force DSD-to-PCM on the output.

Scintilla's picture

In order for this to work, you would need a translation layer between the output of the transport and the input of the hapi. An Oppo bluray player can output DSD into a device that can accept it. But the Hapi has a network interface. I think the easiest way to do this would be a software playwer like HQPlayer or JRiver which can accept the input from the Oppo via an HDMI port and then output to a network interface. I have used HQPlayer for playing CDs live like this from a transport and then back out to a network endpoint device that provides an input to my DAC. I don't see any way to just directly connect a transport to the DAC without this translation layer because I am not aware of any transports that will output over ethernet. You will literally need a computer in between the transport and the DAC.

Kal Rubinson's picture

Yes but, as you note, getting the DSD stream into the computer from a stock-standard disc player is the bottleneck. Sony has made it difficult to move DSD wherever you want.

Auditor's picture

Thanks to both of you for your replies!

I didn't think it was possible, but I was hoping there might be a (simple) option out there I didn't know about. It seems not.

jimtavegia's picture

I have an Sony X700 that has the SACD logo but it actually converts it to 44.1 pcm. Many are having major issues with the X800 model. It also has an HDMI audio only, but I am guessing that is for a Home Theater receiver with HDMI in.

georgehifi's picture

Don't get it. Why not get the product reviewed they make that suits Stereophile readers more.
Like this stereo/streamer dac.
https://nadac.merging.com/product/merging-nadac

"The 8 channels of the ESS Sabre ES9008S Reference D/A converter are merged into 2 channels for improved linearity, greater dynamic range and a lower noise floor."

Cheers George

Kal Rubinson's picture

You are right but we already did that.
See:
https://www.stereophile.com/content/music-round-77
https://www.stereophile.com/content/music-round-90-mergingplayer-pl8

georgehifi's picture

Stereophile is looked at by most/many of it's members I believe for it's measurements which are objective.
So then they can get a "feel" for themselves, if the subjective review is close to the money or not.

Cheers George

Kal Rubinson's picture

Agreed and, as here, now my occasional multichannel reviews now will treated that way going forward (where feasible).

Scintilla's picture

I do think that there are getting to be many more multichannel listeners and many read Stereophile. Kal is not an outlier, rather he is leading into the future of hifi here. But as I have previously noted a few times now, I think the Monoprice HTP-1 is a much better approach for playing multichannel and Atmos material than these free-standing DACs. It already has Dirac with an option for multi-sub bass control, and soon Dirac active room treatment. It employs state-of-the-art AKM 4493s, is quiet, extremely clean and sets up and works with so much greater ease. And because it is a full-featured HT preamp, also provides volume control and switching in an integrated package. It just doesn't do DSD in multichannel from a disc and that could have been the case but they didn't set it up that way. I transcode all my multichannel files in Roon to 24/48 for input and procesing by Dirac. And you get all this for $3999 plus software licenses. In my system, I run parallel front-ends for theater/multichannel and stereo and share the L/R fronts and amplifier between them. I switch the amplifier inputs between the two front-ends with a selector. Best of all worlds and a lot less involved than separates for the same multichannel functionality. As a bonus, I get a great home theater experience. I am waiting for Kal to catch up... :)

georgehifi's picture

"I do think that there are getting to be many more multichannel listeners and many read Stereophile."

If that's the case then maybe the name needs to be changed to "Multiphile" as I believe most dedicated here still have stereo as their main hiend system.
The surround sound sure for the TV in the loungeroom.

Cheers George

Scintilla's picture

So, multichannel isn't of interest to you. It is to many others. You are free not to enjoy multichannel without commenting on those that do or those that express interest in such products, George. You may as well tell the kids to get off your lawn from your porch...

georgehifi's picture

"George. You may as well tell the kids to get off your lawn from your porch..."

No you seem to be on it, going for the personal dig now, so you get off it.

Archimago's picture

"Stereo" from the Greek origins means "solid" as in presence, formed, hardness, concreteness, three-dimensionality.

I know, since the 60's with LP 2-channel, while we typically think of stereo sound as left and right, realize that since the 1940's some of the earliest non-mono playback systems have been 3-channels or more.

I don't think there's a need to change the name Stereophile even if in time there are more multichannel audiophiles!

Kal Rubinson's picture

I've been trying to promote that logic for quite a while. Seems always to be worth repeating.

Archimago's picture

Keep persisting Kal. It's important and IMO the future of audio.

Kal Rubinson's picture

I am trying. ;-)

georgehifi's picture

"I am trying"
http://tinyurl.com/2x35r59f

Without them the review is just subjective, might as well go read "Absolute Sounds" then for some poetic license

Cheers George

Kal Rubinson's picture

Hey, George, my comment was posted in response to Scintilla's post urging a wider/different coverage of multichannel.

...........and it's not your lawn or his.

georgehifi's picture

I cut my grass yesterday, we needed measurements on the http://tinyurl.com/yvqxrxve to keep the "reviewers subjective comments (you) honest", without them like I said it becomes an Absolute Sounds poetic justice type of trust me spend your hard earned money because I said it's good.

Cheers George

Kal Rubinson's picture

Cheers.

Anton's picture

Go, measure!

Nobody stopping you.

JohnnyThunder2.0's picture

you can spend some more time on sites where you agree with the editorial policy than this one where you troll every review with your know it all bs. Stop telling the people at the magazine how to do their jobs. Get a job of your own so we can troll that site. You are rude. Annoying. Hang out on ASR. Stop polluting our site with your trolling nonsense. You do it to every review. You have been called out as a troll on this site before. You're well known as a troll in comments sections and in forums. I wouldnt be proud of that honor.

JohnnyThunder2.0's picture

Find another site to troll. Spend all your days and nights on the ASR site. you do realize that you are in the minority here, don't you. All the major audio sites and magazines are subjective based. You just have ASR. There are no magazines for your kind. No one would read it. People dont read boring negative critiques. YOU BRING THE NEGATIVE. Don't bother. You're going to lose these battles because the magazine and its approach will not change. We like it as it is. Go away troll. ASR is waiting for you.

georgehifi's picture

Yet again just with personal attacks, instead of the topic, sure seems with those statements you make, you can't read/understand measurements.

hollowman's picture

I haven't read this review carefully enough perhaps ... but ... The multi-chnl capabilities of the Hapi device reminds me a bit of this:
https://www.stereophile.com/content/tony-faulkner-engineered-law-average...

Back in 1994, T. Faulkner did comment on combining channels to perform math averaging, down to two channels.
The lab metrics done by JA look outstanding!

Kal Rubinson's picture

I haven't read this review carefully enough perhaps ... but ... The multi-chnl capabilities of the Hapi device reminds me a bit of this:
https://www.stereophile.com/content/tony-faulkner-engineered-law-average...

Back in 1994, T. Faulkner did comment on combining channels to perform math averaging, down to two channels.

I do not see any commonality between a down-mixing algorithm and a discrete multichannel processor. If you do, tell us more.

shaynet98's picture

Kal,
I noted the use case for Atmos recordings and am wondering how you configured your system to allow Atmos decoding from PC?
Cheers!
SHayne

Kal Rubinson's picture

Although I referred to use with Atmos in this review, I did not actually include any Atmos content in it. I acquired the Hapi in time for the review of the Arvus H2-4DA decoder (Stereophile.com/content/arvus-h2-4d-multichannel-dolby-atmos-digital-processor) but I no longer have the Arvus.

In fact, I have no audio system at all at the moment because it is in storage while our apartment is being renovated. Further adventures with Atmos (and other immersive media) will resume when that is completed.

David Harper's picture

Good review as usual. Looks like you've stimulated some commentary and a little controversy here. Good man. When people don't have any important issues to concern themselves with unimportant ones become important.

Desertpilot's picture

Hi Kal,

I appreciate your investigation into equipment needed for Atmos/Auro3D music. I've been content with my ExaSound S88 (5.2 system) for a few years now. I've tried Atmos/Auro3D using 2L's BluRay discs through my Marantz AV8805 processor. It works but I am not so impressed enough to step up to the equipment reviewed here.

Side note: Brendon at TRPTK is releasing both discreet Atmos/Auro3D requiring a decoder and all channels in separate WAV format (huge files) that do NOT need a decoder. We are in a "golden" age for music recording/reproduction!

Marcus
Las Vegas, NV

Kal Rubinson's picture

Brendon at TRPTK is releasing both discreet Atmos/Auro3D requiring a decoder and all channels in separate WAV format (huge files) that do NOT need a decoder. We are in a "golden" age for music recording/reproduction!

Indeed! Brendon is releasing 9.1 (96kHz FLAC, Auro 3D) and 5.1.4 (352.8kHz WAV, Atmos) which are not really "all channels" but the mixdown to that layout. However, given the resolution and the spatial enhancement, they are good enough for me.

hollowman's picture

OFF-TOPIC: Stereophile forum gone? new
Submitted by hollowman on December 26, 2023 - 4:34am
This is the only place on Sterophile to publicly post on this SERIOUS issue/development with Stereophile.

Its long-time running Forum and all content seem to have been VANISHED.
Many of us have contributed time and effort into our posts in the Forum. For almost two decades.
It's OKAY for Stereophile to discontinue the FORUM as Stereophile deems necessary. But please leave the content in place. It's disingenuous to disappear it from existence without proper, public notice.

ChrisS's picture

...here.

Kal Rubinson's picture

????

ChrisS's picture

...

Kal Rubinson's picture

Silly exchange about a now-corrected typo is now over.

hollowman's picture

Freudian algo on that iPhone keypad! (now manually corrected)
Maybe a deliberate cosmic event to flesh out that troll, ChrisS, who read that post carefully and completely, picked out a typo, but weirdly neglects the elephant in the room.
The issue with the Forum is not a joke.
And ... Kal, you lost all your Forum posts and threads, too, over the last two decades. All that investment and effort. Poof!
So why should anyone post in these Comments section, henceforth, if all our content faces a similar existential threat?!

ChrisS's picture

With respect to T.S. Eliot

We are the hollow men
We are the stuffed men
Leaning together
Headpiece filled with straw. Alas!
Our dried voices, when
We whisper together
Are quiet and meaningless
As wind in dry grass
Or rats' feet over broken glass
In our dry cellar...

Anytime, anywhere, we all go POOF!

jimtavegia's picture

Of course with your extensive collection of SACDs I can see why when the digital industry seems to lack the will to keep hi rez alive. Thanks for all you do to keep us informed.

Peprita Heart's picture

Dear Mr. Rubinson ,

In your article there is a photograph of the Horus and Hapi in a rack . Could you please tell me who manufactures the Network switch underneath the Hapi ? If I missed it in your equipment list , I am sorry .

Kind Regards ,
Peprita

Kal Rubinson's picture

I do not know. That picture is a stock photo chosen from Merging and I did not use a switch during this review period. The physical connection between the server and the Hapi was a direct cable link.

The switch I am now using (described in my next review) is a Cisco CBS350-8. It is one of the switches that Merging recommends and for which Merging provides full installation instructions at merging.atlassian.net/wiki/spaces/PUBLICDOC/pages/4819248/Cisco+CBS350-8+Auto-configuration.

Peprita Heart's picture

Mr. Rubinson,

Thanks , I look forward to the review of the switch .

Take Care,
Peprita

Kal Rubinson's picture

I will not be reviewing a switch but I will be using the switch as part of the review setup.

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