GeerFab Audio D.BOB digital breakout box Measurements

Sidebar 4: Measurements

The first test I performed of the GeerFab D.BOB was to examine if its output was bit-perfect—ie, if the bits it outputs via S/PDIF are the same as those sent to it via HDMI. Using my Audio Precision SYS2722, I created a 24-bit S/PDIF signal representing a 1kHz tone at –120dBFS, with triangular dither applied at the LSB level. Fig.1 shows the spectrum of this signal, analyzed in the digital domain (no conversion to analog) by looping the Audio Precision's S/PDIF output to its S/PDIF input. The FFT bins lie at the –180dBFS level, and the noise floor is the spectrum of the LSB-level dither.


Fig.1 Audio Precision SYS2722, digital-domain spectrum with noise and spuriae of dithered 24-bit, 1kHz tone at –120dBFS (left channel blue, right red) (20dB/vertical div.).

I then created an AIFF file from this S/PDIF signal and copied it to my music library. I connected the D.BOB to the HDMI output of my Roon Nucleus + server with a 10m HDMI cable and connected its optical and coaxial S/PDIF outputs to the Audio Precision with an Esperanto coaxial datalink. Fig.2 shows the digital-domain spectrum of the D.BOB's optical output. It is identical to the spectrum in fig.1, proving that the D.BOB's digital output data are identical to the input data.


Fig.2 GeerFab D.BOB, digital-domain spectrum with noise and spuriae of dithered 24-bit, 1kHz tone at –120dBFS (left channel blue, right red) (20dB/vertical div.).

Next, I examined the amount of timing uncertainty or jitter in the D.BOB's S/PDIF output. Using the Audio Precision's digital oscilloscope function, I overlaid successive snapshots of the analyzer's AES/EBU output, sampled at 44.1kHz and taken over a 60-second time window, to show what's called an "eye pattern." The data represented a 16-bit Miller/Dunn J-Test signal, which is a worst-case signal. To make things even harder for the Audio Precision's data output, the AES/EBU link was a 45' length of Canare 110-ohm balanced interconnect. With an ideal transmission system, all the pulse transitions in the datastream will overlay one another to produce an image of a wide-open "eye," with just one trace visible. Fig.3, plotted over one "unit cycle," indicates that this was indeed the case with the SYS2722's output. The average jitter level, assessed with a 50Hz–100kHz bandwidth, was 243 picoseconds (ps).


Fig.3 Audio Precision SYS2722, eye pattern of AES/EBU data output carrying 16-bit, 44.1kHz J-Test data (±3V vertical scale, 175ns horizontal scale).

Repeating this test with the D.BOB's coaxial output gave the eye pattern shown in fig.4. The eye is still wide open, but there is some uncertainty in the beginning and ending times of the multiple traces. The average jitter level was now 1352ps. (Unusually, the jitter was slightly lower with the optical datalink, at 1313ps.) Repeating the test with 24-bit data representing the tone at –120dBFS reduced the jitter in the D.BOB's coaxial output to around 600ps.


Fig.4 GeerFab D.BOB, eye pattern of coaxial S/PDIF data output carrying 16-bit, 44.1kHz J-Test data (±800mV vertical scale, 175ns horizontal scale).

The jitter I found in the D.BOB's S/PDIF output was not high in absolute terms. It will have no effect on sound quality, other than with vintage D/A processors with pathologically poor serial data inputs.

The D.BOB does what it claims to do.—John Atkinson

GeerFab Audio
173 West Bergen Dr.
Fox Point, WI 53217
(414) 446-5841

davip's picture

Once you've purchased the SACD then it's yours to deploy and access as you wish on 'fair-use' terms. I would not care tuppence for the legality or otherwise of the described usage, and I doubt Sony / Phillips / RIAA / Whoever would have a snowball-in-hell's chance of prosecuting. Did anyone who accessed the S-A bitstream from a PS2 to create .diff files ever get prosecuted? No. That's not to say that those corporate swine might not go after Geer, but that's another matter and one assumes that part of the three-years of 'complexity' was his making sure that he wasn't putting his own ass on the line. Well done Him, but your cautions to your readers are, I think, misplaced, and are perhaps a product of today's streaming culture where users are encouraged to adopt the mindset that they don't 'own' the music that they pay for, whether virtual- or physical-media.

My 2p-worth anyway. Once I converted the early Genesis SACDs to their .diff files and transcoded these to 24/88.2 to look at the waveforms and saw that they had all been maximised in a PCM-step, that was the end for me and I gave up on digital entirely.

Props to Geer all the same. I'm back in vinyl heaven -- and my music is Mine...

Kal Rubinson's picture

1. I lean to your perspective on this matter. I have ripped thousands of SACDs and have reported on such activities in Stereophile. OTOH, without an explicit legal opinion in-hand to support the documentation, I took a position of caution on the matter.
2. I am sorry that you had a bad experience with those SACD, most of which derive from recordings made prior CD as well as prior to SACD. The provenance and processing of such are often murky. Not all "modern" SACDs suffer from the same problem.

soundboy's picture

In the Manufacturer's Comment section, GeerFab Audio mentioned there are "roughly 6,000 SACD titles". The real total is more than 14,000. Go to and there are 13,401 SACD titles listed as of this post.

Bogolu Haranath's picture

It was a mistake by Sony/Phillips for not allowing SACD digital data available for external DACs, from the beginning, like they allowed for CD digital data ....... That is my opinion, and I could be wrong :-) .......

jeffhenning's picture

Playing old hi-res audio discs on my BDP-103 via HDMI has worked well, but I never really bought a lot of them. The fidelity of the rock recordings was not always great, but It is nice when you get a decent surround mix.

If I owned a ton of SACD's and wanted to pull them into my Mac, this box might be worth my while. That never happened. I have a lot more Blu-rays and hi-res files.

When I do buy a UHD BD player, I'll still have to hold onto the Oppo to play the few DVD-A/SACD's I do own.

As to legal issues, is anybody really going to bother with that now?

Kal Rubinson's picture


chrisoz's picture

Hi Kal, I decided it was time to upgrade my Ayre C-5xe and purchased the D.BOB from Eric Geer in January. There was no way to buy it in Australia, I had tried online. Eric was extremely helpful even though he was attending NAMM at the time. I use it with a Chord Hugo TT2 and Cambridge Audio CX-UHD transport. The Chord TT2 accepts DSD via DoP on S/PDIF. I have also used it with a Chord Qutest. It has worked flawlessly and I'm completely happy with the D.BOB. I briefly experimented with a Bryston BDA-3 and the Cambridge CX-UHD prior to the arrival of the D.BOB, but find it and the Chord TT2 superior, so much so I no longer own the BDA-3

jeffhenning's picture

There were never all that many hi-res DVD-A and SACD discs that I was interested in. Also, the quality of the rock and fusion releases could be less than stellar.

And the whole bit with the copy protection was a bit onerous.

I'm much happier with Blu-rays and hi-res files.

Kal Rubinson's picture

OK. I found (still find) a lot with music on them that I am interested in but that doesn't include rock and fusion.

The copy protection went away.

Just wanted to know it was not just a snide remark. :-)

jeffhenning's picture

I was unaware of that. Are you just talking SACD's or DVD-A's, too? Most of mine are pretty old.

The last SACD that I bought was Count Basie "Live at the Sands (before Frank)" (MoFi) in 2014. Pretty wonderful stuff. I play it in my Oppo BDP-103 via HDMI into my XMC-1 pre/pro. The Oppo converts it to PCM. Just added it to my "to listen to" list. Got a bunch of hi-res stuff queued up on my rack since I completed the surround system a month ago.

Wonder if I can pull that Basie disc into my computer?

Kal Rubinson's picture

Of course. One can rip CD, DVD, DVD-A, SACD, BluRay, etc. Been going on for a while. I've reported on this in my recently concluded MITR series but its all over the Internet.

ri_stretto's picture

czech company has for at least 15 years offered their vanity boards for oppo and a number of universal players. these boards replaced the stock digital outputs on oppos or were add-ons / replacements for the S/PDIF outputs on universal players.
the vanity boards picked up DSD and PCM streams from the circuit; output was/is either DSD-in-PCM in the case of SACD or PCM in the disk's native sampling rate/word length up to 192/24 when spinning red book or DVD-A. output was either BNC or RCA. alternatively the signal could also be upsampled to 192/24.
i still have an old pioneer DV-656 universal player (IIRC from around 2002 or so) with a vanity board that i use to play the few DVD-A i still have and of course all SACD.
the vanity boards for oppo players put out stereo and multichannel signals as DSD and PCM. do a google search for "audiopraise vanity" if you want to know more.

Kal Rubinson's picture

..................but can you actually buy such a device or a stand-alone convertor from AudioPraise now?

I would!!

Bogolu Haranath's picture

Do you (KR) use any other built-in digital reconstruction filter(s) in the Mytek Brooklyn processor, other than the standard linear phase filter? ........ Just curious :-) ........

Kal Rubinson's picture

I don't really use the Mytek Brooklyn much these days except for testing as described in this review. The multichannel DACs suit my every day needs much better.

Dick James's picture

DVD-A has evolved into BD-A or in some cases DVD-V with hi-res audio, probably because so few players supported DVD-A, and SACD is fully alive. There are hundreds of hybrid SACDs released every year in stereo and multichannel sound.

volvic's picture

I am a very late adopter to SACD and while some of the titles coming from Japan are a little pricey, I still gulp and buy, and whatever I find in the used CD stores has allowed me to amass a small but sizeable collection. I think if SACD had launched in 1982, none of us would have turntables today. Not as good as vinyl on every release, but on others tough to ignore how good SACD is.

shib's picture

For audiophiles like me who do not care to spend the time to download files or stream, this product is useless because it still requires a physical player, whose laser or disc mechanism will die. I have the Sony SCD-1 player and was bit in the ass when Sony stopped making replacement parts. I want my "last" SACD player. I prefer it to have DAC inputs, but can live without. The manufacturer must guarantee replacement parts. The new Denons seem like a good choice, since their transport has seem to become the new industry standard. In the meantime, while I wait for my Cinderella SACD player, I'll just continue to listen to my vinyl. Forget about spending $thousands on a SACD player that will, not may, die. I'll spend that extra money on records or a new cartridge.

Bogolu Haranath's picture

You could consider the Denon DCD-1600NE CD/SACD player, $1,199 :-) ........

shib's picture

Except I'm greedy and want it all. My SCD-1 was probably one of the Top 10 best built SACD players. Hard to step down mechanically. And, can't Denon throw in some DAC inputs? I do see working used lasers on eBay for my Sony. I also have a used spare that I replaced but kept. The player also needs to be recapped. I may go that route. Don't really see what the point is for me to spend a lot of $ on a new SACD player. I listen mostly to vinyl anyway.

Bogolu Haranath's picture

Denon's sister company Marantz makes SA-KI Ruby CD/SACD player which also has built-in DAC ...... It is more expensive, $3,999 :-) .........

bobrapoport's picture

Hi Kal,

With all due props to Eric and D.Bob, Essence has been making proper audiophile class HDMI DACs since 2013. You liked our Evolve II-4K HDMI v2.0 Multi-Channel model a couple of years ago and at $299 it can playback Native DSD on SACDs over HDMI along with uncompressed, native PCM Hi Res files on Blu-ray. We are honored to be listed in the Stereophile Recommended List.

We have a step-up model called the HDACC II-4K DAC at $649, it has 4 HDMI v2.0 inputs for sources like Nvidia Shield and Apple TV4K, 4K Universal Blu-ray players, the latest gaming consoles, and the best servers and streamers. It has one HDMI v2.0b output that feeds the 4K video to the TV plus USB in, Optical and Coaxial in/outs. Featuring 32 bit / 384K processing, I use the ESS SabrePro9038 DAC chip to achieve THD + N spec = .00001% at -141 dB s/n ratio, making it a reference class DAC. RCA and XLR analog outputs, remote control, Fixed and Variable output so it can be used as a full function preamp and headphone amp as well as a stand alone DAC. The OLED display reads the inbound sample rate of the source, input selection, upsample menu, and volume.

This device is legal and it uses the latest HDCP v2.2 to unlock the layers of an SACD or Blu-ray disc to reach the highest native bit rates, equal to a one to one copy of the original master recording. My customers think highly of the device, I've shared 27 user experiences on my product page, just click on the stars in the upper right hand corner here: to learn more, they are quite insightful.

Its a great way to update older vintage audio to remote control and the latest digital media sources and will make anything its connected to sound better. It can upsample older formats like CD up to 24/96K for a nice lift in performance. It also has a single analog input with a nice A to D converter for vinyl and tape sources. Its a problem solver, the Swiss Army knife of DACs according the John Darko.

One note about using an optical or coaxial output from a DAC being fed an HDMI source, the HDCP will downgrade the bandwidth of hi res content to no higher than 48K sample rate output over SPDIF connections. Copyright laws prohibit the recording or storage of the highest resolution audio and highest definition video. So the only way to achieve the highest performance is via HDMI v2.0b with HDCP v2.2 both in and out. The highest resolution audio is encrypted, security authentication via a 2 way digital handshake is required for decryption.

The Fairness Doctrine expired in 1997 when the DMCA Act became the law of the land. We can watch and we can listen but we are not allowed to copy. The content creators who own the copyrights to their art are in control now. Its a fair trade off in my book.

I'd be happy to provide you with an HDACC II-4K to try, just let me know.

Bob Rapoport, CEO
Essence For Hi Res Audio