Up ‘N’ Oversampled
Magnificence
The Dodson DA-217 MK2-D Digital Processor

BY LARS FREDELL


here is a lot of talk about improving the recording and reproduction of digital recordings nowadays. If it’s not the exuberance over the discovery of what the DSD/SACD system might be able to accomplish for us audiophiles, it is surely the wistful yearning for a competing DVD-A system to take us from here to “there!’ The DSD/SACD proposition seems painfully slow and phlegmatic in its advancement (if you can even call it that) towards fulfilling its initial promise. When are we going to see some software that takes advantage of DSD recording techniques? Apart from a few small, daring labels, we have so far only seen old Sony (Columbia) staples regurgitated. And, they still carry the drawbacks of ancient (well, in a stereo sense!) recording techniques. Give us some new stuff now! While you’re at it, give us some cheaper and better players, too!


The DVD-A phalanx doesn’t seem to be able to get to first base. They’re so skittish about security of their copyrights that they cannot see the bits for the digits. Why wreck a high-resolution recording system with a security watermark that is bound to damage the musical content? Especially since some snot nosed 14-year-old hacker, who ought to busy himself with homework instead, will soon crack any security code and hang it out for general consumption anyway. Why don’t they just throw the axe in the lake and get on with the music? Phew!
Am I dissatisfied with digital’s current state of affairs? You betcha!
Techniques have been developed for real high-resolution audio, but I’m prevented from enjoying it because a bunch of suits think that they can have their cake and eat it, too. I’m fearful that the whole promise of high-resolution audio will fall by the wayside in favor of some half-baked DVD derivative that might make the masses happy but not many audiophiles. What a waste of a great opportunity! That ends my rant. You might wonder what prompted this outburst? Impatience. We have these potentially great new recording systems but precious few recordings that have taken advantage of them.
 
BUSY BITS
In the meantime, however, a lot is going on with our standard PCM 16/44.1 CDs. Recordings are getting better and better (witness the new batch of outstanding Chesky CDs), as is the playback equipment. Lately, a lot of attention in digital replay is being paid to upsampling. Upsampling is simply a means to add (arithmetically) more interpolation points between those that are recorded through the 44.1 KHz sampling rate. It is important to make a clear distinction between sampling, upsampling and oversampling. Our current CDs (excepting the few available SACDs and 24/96 DVD-As) are sampled at 44.1 KHz. That means that a musical signal, when recorded, is sampled 44,100 times per second and each of these samples (bits) becomes a point of interpolation. The bits come batched together in 16 bit words by the A/D for decoding in a DAC. Thus the 16/44.1 denomination. The 24/96 recording process increases the sampling rate to 96,000 times batching in bigger 24- bit words, thereby significantly improving the resolution of harmonic detail, etc, as well as increasing the frequency bandwidth (see the Nyquist theorem). On the other hand, DSD/SACD samples the signal over 2.8 million times; the DAC then decodes the samples one bit at a time. This is called direct bitstream and when properly implemented can provide a very high level of resolution. Upsampling takes place when a 16/44.1 (or other sample rate) is converted into a higher level such as 24/96 or 24/192, or higher.

Upsampling, although a purely binary extrapolation process (ie, a mathematical reconstruction), can have a beneficial effect on the sound of a standard 16/44.1 CD.
54 • ULTIMATEAUDIO, FALL 2000

 

  Am I dissatisfied with
digital's current state
of affairs? You betcha!

Finally, the concept of oversampling relates to a method of pushing the digital noise (a result of the conversion process) up to a higher frequency area, well beyond human hearing. Most DACs are oversampling at least twice, but some do it four, eight or more times.

DARING BITS
I’m going into this detail on sampling because the new Dodson DA-217 MK2-D is blowing me away! I’ve lived with a Dodson DAC as part of my reference system for several years, going from the original DA-217 to the upgraded Mark 2 and now this amazing latest version, the Mark 2-D. They’ve all been great, but this new one is really special!
Ralph Dodson is a retired scientist from the “secret” black box division of General Dynamics. He has, as he says, spent at least half of a lifetime designing digital circuits for warplanes and missiles as well as space rockets. Rather than sitting on a San Diego beach among other retirees, he’s putting this tremendous experience to use in designing one of the finest digital products I’ve seen. He knows that to get it right, every little detail must be optimized in the digital-to-analog conversion process. “I can’t do much about the recording/encoding process,” he says, ‘but I can try to optimize the decoding process by designing crucial elements with great care. There is a lot more to get out of a regular 16/44.1 CD than we’ve been able to do so far.” Damn right!

The new version of the Dodson is the result of painstaking evolution of a design that goes back 15 years. Part after part, element by element, the design has been optimized utilizing the best components available. Think about it. Here’s a guy with 30 years of high-quality, often critical, digital design experience persistently refining his audio design over 15 years. Fanatic? Yes, I guess you could call him that, but Ralph Dodson might prefer descriptors like meticulous or fastidious. Whatever; it’s amazing either way you put it!
The MK 2-D is a complete 24/96 KHz design. This means that any given input signal (16/32 KHz, 16/44.1 KHz, 16/48 KHz or 24/96 KHz) will be treated as a 24/96 KHz signal. Thus, anything that isn’t a 24/96 KHz signal is converted into one by the process of upsampling. Once upsampled, the now 24/96 signal is then oversampled eight times to an astounding 768 KHz before being decoded (at the absolutely blinding speed of 25 MHz!). Thus, for all practical purposes, the Dodson DA-217 MK 2-D is a 24/768 DAC!
The phenomenal computing power of the DA-217 MK 2-D allows for an analog filter with an effective bandwidth of 100 KHz (see Technical Highlights). “What good is that,” you ask, “since humans can’t hear much above 15 to 16 KHz?” This is a much-debated issue, and I don’t want to stoke the various fires by showing my

 

own ignorance. However, based on my personal observations it would appear that, for instance, a wider bandwidth certainly can be very beneficial to the harmonic content of the music. A case can probably also be made for better dynamic contrast and perhaps for other parameters as well. After all, who in their right mind would buy a preamplifier or amplifier with a bandwidth limitation at 22 KHz as the current CD redbook standard prescribes?
Playing some new DVD-A 24/96 CDs from Chesky it was pretty obvious that the Dodson offered a level of resolution well beyond that of the normal 16/44.1 CDs. The bass was significantly better with more realistic transient attack and more extended and truthful decay. The mids were better developed with better resolution and transparency that made it easier to identify instruments’ location, size and timbral characteristics. Likewise, the top end was unfatiguing and smooth, extending way out. My favorite peeves—unnatural sibilance and cymbals as well as strident massed first violins—came across just right. Indeed, it was quite an experience.

COMPARABLE BITS
How does it compare to my reference high-resolution digital player, the Sony SCD-1 playing SACDs? It’s impossible to say in the absence of comparable DVD-A and SACD recordings of the same event, but both systems sure offer a worthwhile improvement over current standard. It may well be a while before we can determine which one is better. Subjectively, I still feel that SACD produced a better- delineated and more dimensional soundspace. On the other hand, the DVD-A might have the slightest advantage in dynamics. As I said, it is very difficult to determine with available software, so I may well be wrong.

Truth be told, while I appreciate the Dodson’s ability as a high-resolution DVD-A decoder, this is not why I’ve been so
55 • ULTIMATEAUDIO, FALL 2000

 

Dodson
utterly blown away by it. Excellent as the new 24/96 Cheskys are (and they’re really something special’), I still don’t have enough music that I love on DVD-A, or on SACD for that matter. Nothing I played could engage me like some of my older CDs can, in spite of the additional insights into the musical event offered through the higher resolution
What really excites me to no end about the DA-217 MK2-D is what it does to my several thousand regular 16/44.1 CDs! It is quite clear to me now that there is more to our standard CDs than what I have experienced with the various DACs and CD players I’ve used in the past. I know that it may not be real in an authentic sense. But whatever interpolation Dodson’s algorithms perform on the basic samples sure as hell sounds realistic to these ears. To coin a famous phrase from my buddy ST: There is definitely more “there” there!
All (and I mean all) of my CDs passing through the Dodson displayed a better “understanding” of what went on at their recording. There is more harmonic richness, better dynamics, better-developed frequency extremes and a much better sense of the recording venue than I’ve heard from the same CDs during hundreds of previous listening sessions. What’s happened to some of these CDs is almost miraculous. No, of course it is not the same as an SACD or a DVD-A, but in some respects it comes surprisingly close, it seems. Clearly, on some CDs there was a greater difference between the original 16/44.1 replayed as such and the up ‘n’ oversampled version than I could discern between the latter and a SACD version of the same CD. In other words, the Dodson version at 24/768 was closer to the SACD than it was to itself when played as a normally decoded 16/44.1. I know that some of you might get a slight headache from reading what might seem like such a preposterous statement. However, that’s what I heard.
I’ve had other 24/96 DACs in my system, with and without upsamplers/oversamplers of a similar type (maybe not as advanced as 24/768, but certainly 24/192) and they never produced anything like the results I’ve heard with the Dodson DA-217 MK2-D. The Dodson is by far the best CD playback device I’ve ever heard, rivaled only by the Sony SCD-1 when playing SACDs (Ralph is working on a DSD chip for future upgrading capability to SACD). The smoothness and liquidity is awesome, the

TECHNICAL HIGHLIGHTS
ot much has changed on the outside of the Dodson DA-217 MK2-D compared with its predecessor—save for the name, and the fact that the HDCD indicator has been changed to a DVD light. All the other functions, including the polarity reversal, are still there.
Changes, both several and significant, are found in the innards of the DA-217 MK2-D. As the input signal (32, 44.1, 48 or 96 KHz sampled) guided by its original clock enters the DAC, it is immediately changed from single ended to fully balanced by means of a proprietary circuit designed by Dodson. The signal then goes into a digital receiver where the clock is recovered and separated from the signal. The clock signal goes into a PLL (Phase Lock Loop) for “clean up” and removal of any jitter and is then used to clock the data into a memory buffer. A master system clock, with ± 2 Pico second phase jitter is used to remove the stored data from the memory buffer. The now jitter free data is passed on to the upsampler where it is upsampled to 96 KHz. This upsampler has a new, and very advanced, algorithm.
The signal coming out of the upsampler is always 96 KHz as it is transferred to the digital filter, which oversamples it eight times to 768 KHz. Then the 24/768 signal goes in to a second re-clocking circuitry this one controlled by the master system clock and a reclocking oscillator running at a phenomenal 25 MHz (virtually all other DACs are running at a fraction of this, for instance the Sony SCD-1 is running at 2.8 MHz), to prevent any reintroduction of jitter on the up- and oversampled signal. The 25 MHz re-clocking is also, separately, controlling the digital-to-analog converter where the signal is converted to analog before passing on to the analog filter. The analog filter has a 100 KHz bandwidth and is of an FDNR-type (Frequency Dependent Negative Resistor) with less than ± 0.04 degrees of phase shift. Finally, the signal passes through a buffer/driver stage for output.
The truly unique aspects of this design lie (among other things) in the proprietary circuitry in the input receiver, which has been tested and perfected over many years. In addition, a Faraday shield protects the whole digital section and the circuit boards are 4-layered, using fully differential paths inside the boards; these aspects protect the signal from undue outside interferences. Dodson obviously carefully picked the algorithm options to give the desired Dodson specifications.
To manage the enormous information flow of 24/768 conversion, Dodson employs a 25 MHz re-clocking oscillator to control the re-clocking circuitry. By current standards in digital audio this is, in all probability unheard of.
At the final checkout stage in the manufacturing process there is a very detailed control of left and right channel phase shifts. Both channels are adjusted to the very fine tolerance of 0.04 degrees of each other.
The Dodson DA-217 MK2-D is a technological masterpiece in all its simplicity. It is a meticulous design by a master craftsman who sets the music before everything else and who eschews any unnecessary bells and whistles.
“you-are-there” feeling is much enhanced by the extra sense of “air” and dimensionality and the soundspace just devours you. Unreal! (Exclaimed here as a positive, not as a descriptor.) If the high-resolution replay systems and recordings do not become a reality in the near future, it would be a pity for sure. But the extraordinary Dodson DA-217 MK 2-D has brought us a long way, and I can live with that. Actually, now I can’t live without it.

Dodson DA-217 MK2-D Digital Processor, Dodson Audio, 14340 Marianopolis Way, San Diego, CA 92129. Tel.: (858) 484-8199.
Web site: www.dod
sonaudio.com.
Frequency response: 20 Hz-45 KHz; Channel separation: >110 dB @ 1 KHz. Digital domain, sampling frequencies: 32 KHz; 44.1 KHz; 48 KHz and 96 KHz (automatically selected). Output voltage: 2.3 Volts RMS. Digital inputs: 2 Coax, 1 Toslink (AESIEBU or AT&T ST optional). Analog outputs: single-ended (RCA) and XLR outputs. Absolute polarity switch: Yes, Upgradability: the Upsampler module, Microprocessor, Digital filter and Analog IC’s socketed for future format upgrades. Detachable power cord: Yes. Dimensions: 3 x 17 x 12 inches (h x w x d); Weight 16 lbs. Price: $4,995 (Optional: AES/EBU: $250; AT&T ST: $275).
56 • ULTIMATEAUDIO, FALL 2000

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