Audio Alchemy Digital Decoding Engine v1.0


The $399 Digital Decoding Engine is for real.

But how can Audio Alchemy make an outboard D/A converter for about half the price of the next most inexpensive decoders (the PS Audio DigiLink and Melior Bitstream D/A)? Can it be any good? These were my first reactions to the DDE, and I'm sure many of you are asking these same questions.

First, however, some background on the company: Audio Alchemy is the name of a new line of digital products manufactured by the California-based LM Acoustics. The company's other products include a Digital Transmission Interface ($299) that goes between a transport and processor, a two-piece CD transport ($699), the Clearstream digital coaxial cable ($49), and the Analog Decoding Engine ($199) that "conditions" the analog output from a D/A processor. Looking at their line, it is clear that Audio Alchemy is attempting to boldly go where no digital manufacturer has gone before—at least in price.

In addition to making the Audio Alchemy line, LM Acoustics designs and manufactures a variety of audio products for many companies. The Music and Sound DCC-1 that I reviewed in March, for example, was designed and built by LM Acoustics. The company is currently working on several other, more ambitious digital products.

Does the Digital Decoding Engine bring a new level of affordability to digital processors, or is it a toy that can't compete with established yet affordable performers like the PS Audio SuperLink and Meridian 203?

Let's find out.

Technical description
The Digital Decoding Engine (DDE) is so small and light that many people do a double take when they find out it's an outboard D/A converter. Easily held in the palm of the hand, the diminutive DDE isn't what we've come to expect D/A converters to look like.

Despite its small size and low price, the DDE has the features of the full-sized (and -priced) outboard decoders. Coaxial and optical inputs are provided (on RCA and Toslink jacks), with a front-panel selector switch. The front panel also includes an absolute polarity switch and three LEDs that indicate when the unit is locked to an incoming digital signal, and that the analog and digital power supplies are working.

The rear panel holds the previously mentioned RCA and Toslink input jacks, as well as a digital output for driving a DAT machine or future digital recorders having S/PDIF (Sony/Philips Digital Interface Format) digital inputs. Analog output is provided on two RCA jacks, which, like the digital input and output, are gold-plated. A mini-jack accepts ±12VDC from the outboard power supply, a 2" by 2½" by 1½" box.

An unusual feature of the DDE is the I2S Bus found on a rear-panel DIN connector. The I2S Bus (pronounced "I squared S") provides access to the raw serial 16-bit digital audio data after it has been decoded from the incoming S/PDIF delivered by a CD transport just before the D/A converter. This allows digital signal processors to be connected to the DDE while keeping the signal in the digital domain. The I2S Bus can be thought of as an expansion slot in a personal computer: both provide a communication path between the device and the outside world. At Audio Alchemy's CES booth, I saw a prototype Digital Signal Processing (DSP) box that connects to the DDE's I2S Bus and is controlled by a personal computer, providing a variety of signal-processing functions including equalization and reverberation enhancement. The I2S bus also allows the user to plug in a newer, upgraded D/A converter to the DDE without the expense of replacing the entire input and demodulator stage, chassis, and other hardware. Don't be surprised to see future products from Audio Alchemy that use the latest DACs, yet connect directly to the DDE.

Popping the Engine's hood revealed a compact, efficient topology and layout. Despite the extraordinarily low price, the DDE's designer didn't take a cheap-as-possible approach—several design touches adding to the unit's cost could very easily have been omitted.

The power supply, which consumes about 15% of the printed circuit board real estate, consists of four regulation stages: +8V and –8V stages supply the output op-amp, +5V supplies the input decoder and demodulator, and a second +5V regulation stage powers the Bitstream chip. Each stage is regulated by a three-pin regulator, and filtering is provided by two electrolytic caps, one 1000µF and one 470µF. This internal supply is driven by ±12V DC from the previously mentioned outboard unit, which contains a power transformer, two full-wave bridge rectifiers, and two 2200µF filter caps bypassed with 0.01µF caps. The choice of a 12V output from the power supply is deliberate in order to allow the DDE to be used in car stereo applications.

The chip set is the Philips SAA7274 S/PDIF receiver and decoder coupled with Philips's SAA7323 Bitstream DAC/filter chip. The S/PDIF receiver circuit is unusual in that a Voltage Controlled Oscillator (VCO) supplies the reference Phase Lock Loop (PLL) frequency rather than the ubiquitous crystal clock generator. An additional chip next to the 7274 gets a reference voltage from the 7274 and outputs a frequency back to the decoder chip. This circuit's job is to recover the clock imbedded in the incoming S/PDIF signal. This technique reportedly results in lower clock jitter than standard PLL implementations (several hundred picoseconds rather than 2–5 nanoseconds). In addition, the DDE will lock to any incoming sampling frequency between 40kHz and 50kHz, but won't accept the 32kHz sampling frequency used in DAT's extended play mode and Direct Broadcast Satellite (DBS). This circuit is a good example of my impression that the DDE wasn't built strictly on price; the VCO technique added more parts and design time to the DDE, yet wasn't essential to its operation.

The 7323 Bitstream chip incorporates the digital filter, Bitstream DAC, and analog output stage. Audio Alchemy has chosen to bypass one of the 7323's analog stages in favor of a single Analog Devices AD746JN dual bi-FET op-amp, shared between left and right channels. (The first op-amp in the 7323 is part of the switched capacitor network and can't be bypassed.) Again, replacing the 7323's internal op-amp with the moderately expensive AD746JN reflects the attempt to make the DDE sonically competitive, not just price-competitive.

Output muting is accomplished by tying the front-panel lock indicator to the Bitstream chip, muting the output until the unit has locked to the incoming digital signal. De-emphasis is performed by the 7323 Bitstream chip in the analog domain with an internal resistor/capacitor pair.

All resistors are metal-film types, and capacitors are polystyrene and polypropylene. The very simple design is executed with a minimum of parts. Although I was surprised to learn that a company could build and sell a $400 D/A converter (especially an American-made product sold through normal retail channels), I was even more surprised after looking inside the Digital Decoding Engine. Despite its simplicity and economy of construction, it nevertheless looks like it should retail for more than $399. According to Audio Alchemy President Mark Schifter, the DDE's retail price is in line with standard industry pricing based on parts cost. The low actual profit (as opposed to profit percentage) is reportedly made up for by selling a lot of units.

My first impression upon hearing the Engine? Competent—even surprising—but not outstanding in relation to more expensive processors like the Meridian 203 and PS Audio SuperLink. Considering, however, that the DDE costs not even two and a half times less than the next cheapest processor to which it was compared, its performance was very impressive.

What the DDE gives you that is often missing from cheap CD players is detail, transparency, and clarity. In this regard, the DDE has more in common with the good outboard decoders than with low-priced CD players. Through the DDE, there wasn't the opaqueness and detail-obscuring haze overlaying the music so often heard from inexpensive digital playback. The music had a vibrant immediacy and palpability rather than a congested, lifeless character. In addition, instrumental outlines were clearly defined, creating the impression of individual instruments in the soundstage. Many high-priced decoders don't do this well in delineating image outlines, an important factor in rendering the illusion of musicians in the listening room.

Compared with the Meridian 203, the DDE had a more sharply focused rendering and greater resolution of instrumental outlines. The 203, however, offered a greater sense of the instruments being surrounded by air and space. This was more apparent on naturally miked recordings, giving the 203 a clear edge on classical music and most jazz. Through the DDE, the soundstage was vivid and sharply defined, but lacked the impression of instruments floating on air between the loudspeakers. Herbie Hancock's piano on the excellent Jack DeJohnette album Parallel Realities (MCA MCAD-42313, Vol.13 No.9) had less air surrounding it and appeared more forward in the soundstage with the DDE than through the 203 (footnote 1).

In addition, the illusion of space and soundstage depth was easily superior through the 203. I felt the DDE's presentation was too forward and lacking an ultimate feeling of size and space. The 203 threw a much more accurate rendering of hall acoustics and space. Julianne Baird, for example, on The English Lute Song (Dorian DOR-90109), was farther forward in the presentation, drier, and less enveloped in the gorgeous acoustic of the Troy Savings Bank Music Hall when reproduced by the DDE. However, the distinction between lute and voice was greater through the DDE. The Stereophile recording of Brahms's Piano Sonata in f, from the Intermezzo CD (STPH003-2) was particularly revealing of the DDE's limitations in reproducing space. The DDE made the room seem much smaller and didn't reveal the wealth of natural ambience on this recording. Through the 203, the soundstage suddenly expanded, with room reflections becoming clearly audible at the soundstage's edges.

Similarly, the DDE had a more forward rendering than the 203, but less resolution of inner detail and finely woven textures. The DDE seemed to present all its detail right up front, rather than in layers and layers of subtle gradations. In this regard, the 203's presentation was more relaxed, interesting, and musically involving. I preferred listening into the music to hear inner detail and nuance, rather than having lots of detail thrust forward. The DDE's forward and highly detailed character tended to make long listening sessions fatiguing. In short, the DDE's presentation of musical information was somewhat blunt and aggressive, the 203's refined and gentle.

One area where the DDE clearly bested the 203 was in conveying the energy and rhythmic drive of music. The DDE's bottom end had a punch and solidity that was particularly satisfying. In addition, there was a greater feeling of what Martin Colloms aptly describes as "pace." I found myself tapping my foot quite often when listening to the DDE, always a good sign. This is perhaps the result of the DDE's fuller, weightier bass presentation, something that made bass guitar lines seem to bounce more with the rhythm. Contributing to this impression was the DDE's more dynamic character. Snare and bass drum seemed more dynamic and punchy, adding to the feeling of drive and energy. Neither processor, however, was a match for the SuperLink in either dynamics or bass drive. I've yet to hear a 1-bit converter approach the bass tightness, authority, and dynamics of a good multi-bit–based processor, especially the outstanding SuperLink.

My main complaint about the DDE was the treble. It tended to be forward and hard, especially during peaks of high recorded signal levels. Cymbals were more prominent in the presentation than is natural, and the upper harmonics of high-frequency–rich instruments were overly emphasized. The delicacy and air in cymbals heard through the 203 were missing from the DDE's rendering. I've found that many 1-bit decoders tend to get hard as signal level increases; the DDE was no exception. Snare drum, with its high peak level and substantial high-frequency component, was particularly edgy. The snare-drum dynamics just mentioned were perhaps more the result of this hardness than of actual dynamic contrast; brittleness and edge give the impression of greater volume.

Instrumental textures, while detailed and vibrant, tended to be a little synthetic sounding. There wasn't that lush liquidity and warmth that conveys an instrument's true tonal shadings. Listen to Joe Henderson's unaccompanied sax that begins "Ask Me Now," from McCoy Tyner's new Chesky CD (New York Reunion, JD51). Through the DDE, it was somewhat sterile, lacking warmth and body in the midrange, and a little edgy. By contrast, the 203 presented a much more believable rendering, with roundness, breath, and liquidity. The SuperLink also bested the DDE in ability to present natural timbres. In this regard, the DDE clearly sounded "digital" rather than more closely emulating good analog.

In remembering my experience with the identically priced Rotel RCD-855 CD player, I feel the DDE to be more detailed, and to have sharper soundstage focus and a more forward and vivid presentation than this popular CD player. The 855, however, was more laid-back, less fatiguing, and had better soundstage depth. Despite these factors, I would have to chose the DDE for its transparency, clarity, and soundstage delineation.

On the credit side of the ledger, the DDE is remarkably transparent, with a surprisingly well-focused soundstage. The DDE didn't homogenize instrumental outlines, a trait so common in inexpensive digital playback. In addition, this diminutive unit had good bass drive and ability to convey the music's rhythm. Finally, the DDE had lots of detail; I never felt I was missing a large part of the music, another characteristic of low-priced CD players.

On the debit side, I found the treble a bit hashy and forward, lacking the delicacy and nuance heard through the Meridian 203. Although the DDE's soundstage was superbly defined laterally, it lacked the sense of depth and ability to surround instruments with the recorded acoustic. This gave the entire presentation a forward immediacy that could become fatiguing after a long session. In addition, instrumental textures were somewhat synthetic and lacking the liquidity and roundness heard through other (admittedly more expensive) processors.

Overall, I preferred the Meridian 203 on classical music and most acoustic jazz. With some electronic music in which soundstage depth and accurate tonal shadings are less important, the DDE, with its superior rhythmic drive and sharper soundstage focus, ran a much closer race. I should reiterate that not only is the Meridian 203 two and a half times the DDE's price, it is, in my opinion, the best of the $1000 processors.

For music lovers on a budget, I can't recommend the Audio Alchemy Digital Decoding Engine more highly. While it has some sonic shortcomings, it nevertheless offers a level of musical performance previously unheard of at this low price. In addition, it is well made, incorporates most of the bigger units' features, has a five-year warranty, and is upgradable through the I2S bus when newer DACs become available.

For $399, therefore, the Audio Alchemy Digital Decoding Engine is a bargain. It's no giant-killer, but if you own an inexpensive CD player with a digital output and have been wanting to upgrade to an outboard processor, the DDE might be just the ticket.

Footnote 1: It's great to hear Herbie play acoustic piano again.
Audio Alchemy, Inc.
Company no longer in existence (2014)