T+A Elektroakustik DAC 8 Review

The T+A DAC 8 has been in my audio system off and on for several months. There was something about this DAC that just didn’t sound right for much of this time period. I knew the DAC 8 was engineered very well with several user adjustable settings and DSP unique to the T+A brand, so I continued using the DAC in between reviews of other products. I had faith in the DAC 8 but admit at one point I even started writing an email to prep T+A for an unfavorable review. Roughly two weeks ago I decided it was time to fish or cut bait. I couldn’t hold up the review any longer. In my last ditch effort to squeeze better sound from the DAC 8 I re-read the user manual and discovered I wasn’t using the correct digital filter for my musical taste. This entire time I thought I’d set the DAC up to use its pure Bezier interpolator for better timing and dynamics. To my dismay I’d accidentally selected the Bezier interpolator with IIR filter that produces a highly analog sound similar to vinyl records. There’s nothing wrong with the Bezier interpolator with IIR filter but it was far from my expectations of accurate playback. Once I selected the pure Bezier interpolator all was right with the world. I’d found the magic I knew was inside the T+A DAC 8 and couldn’t have been happier.[PRBREAK][/PRBREAK]

The T+A DAC 8

The first ten times I used the T+A DAC 8 I was sorely disappointed. How could something with such potential underwhelm me to this degree? Was the DAC 8 bound to be the Shawon Dunston of the HiFi world? I had no answers to these questions but I had hope for this product. Fortunately there was no pressure from T+A to get the review done and the company offered all the help I needed when questions arose. By the end of my time with the DAC 8 I had the DAC singing beautifully. The T+A DAC 8 is capable of very good sound indeed.

The T+A DAC 8 is built very well with an all aluminum case. The top plate is impressive and oozes quality in both looks and feel. The physical size of the DAC 8 surprised me a bit when I unboxed the unit. The DAC is almost twice as large as I expected based on my perusal of the T+A photos.

The DAC features several digital inputs, a coaxial digital output, and two analog outputs. The single ended and balanced analog outputs are powerful enough to drive an amplifier directly according to T+A. In my system I opted to use the rear switch to enable Line Out for the analog outputs rather than variable output. Line out simply disables the internal volume control and sends an unaltered analog signal to a preamplifier. The plethora of digital inputs should be enough for nearly all computer audiophiles. During my review I used the AES/EBU, BNC, and USB inputs extensively. All three of these inputs support samples rates through 192 kHz at 24 bits.

Internally the DAC 8 has separate power supplies for the analog and digital sections. Continuing on the theme of analog and digital separation T+A claims complete galvanic isolation between the digital and analog sections as well. The DAC 8 uses magnetic i-couplers from Analog Devices to all interference from the digital source getting to the analog portion of the DAC. T+A is a strong believer in this galvanic isolation stating the, "enormous levels of interference which would ruin the superior sound qualities of the audiophile output stage without this measure."

The DAC 8 employs a quadruple array of four stereo 32-bit converters from Burr-Brown in a double symmetrical circuit. This circuit compensates for non-linearities and reduces background noise by 6dB. Once data is converted to an analog audio signal it flows to fully discrete and symmetrical analog output stages. T+A doesn't use any operational amplifiers in the DAC 8.

Before discussing sound quality I'd like to take a step back and look at the Digital Signal Processing capabilities of the DAC 8. T+A has been developing its own DSP for decades. The DSP chip in the DAC 8 uses 56 bit precision when over sampling with T+A's own algorithms. T+A uses a fairly unique clock generation approach similar to use a belt and suspenders. If one method doesn't work then a second will be engaged. When data is first received it's processed and decoded. The clock signal is derived from the data stream itself and is sent to a PLL for jitter cleansing. The DAC 8's micro processor then analyzes the cleansed data for frequency and stability. If the data meets T+A's specifications then the DAC chips are switched to master clock mode with low phase noise. In master clock mode the clock is generated by two quartz oscillators, one for the 44.1 kHz family and the other for the 48 kHz family. However, if the incoming data isn't cleaned up enough by the initial PLL a second PLL stage is used rather than the dual quartz oscillators. Throughout the entire review period the DAC 8 indicated it had a signal lock for the first stage of PLL clocking and indicated it was using both quartz oscillators rather then the second PLL stage.

Digital Filters and Analogue Reconstruction Filters

The DAC 8 filter options, both analog and digital, have a major impact on sound quality. Most DACs use an automatic filter selection process that gives the user no options. If the user doesn't like the sound of a DAC, it's time to move on to the next DAC. The T+A DAC 8 features four digital filters / over sampling options and two analog reconstruction filters. User selectable options in digital domain include a long finite impulse response (FIR) filter, short finite impulse response (impulse optimized), Bezier interpolator plus infinite impulse response (IIR) filter, and my personal favorite the Bezier interpolator. Long FIR filters are very popular in current DAC designs. The inherent weakness of these filters is the pre and post echoes added to the audio signal. Short FIR filters minimize the echoes but can suffer from linearity issues. To work around the flaws of FIR filters T+A developed Bezier polynomial interpolators. Throughout most of the review I used these Bezier filters. There isn't a right or wrong Bezier filter choice rather this selection should be based on personal preference. The Bezier interpolator plus (IIR) filter is what I accidentally used for several months. According to T+A this eliminates the pre echoes of the FIR filters and produced measurable performance similar to a good turntable. Based on my experience with this filter T+A's statement is very accurate. Many audiophiles prefer the sound of analog sources such as turntables and tape. I'm willing to bet these users would be happiest with the Bezier interpolator plus (IIR) filter. The last over sampling option, the pure Bezier interpolator was a game changer for me. This filter eliminates both pre and post echoes and is said to be the most accurate with good dynamics. Based on my use of Spectral Audio components readers have probably guessed I prefer high speed and accurate sound reproduction. Thus, the pure Bezier interpolator was a no-brainer as my favorite option. Too bad I screwed up early on with my accidental selection of the Bezier / IIR filter.

The analog reconstruction filter options in the DAC 8 may confuse many readers and seem unnecessary to the die hard scientific types. No worries either way. A simple listening session can determine which filter is best in any system. Plus there are no extra high end audio charges for a DAC that operates up to 120 kHz instead of only 60 kHz. The frequency bandwidth of the analog reconstruction filter operates in Normal mode up to 60 kHz and up to 120 kHz in Wide mode. T+A recommends use of high bandwidth amplifiers capable of frequencies up to 300 kHz without distortion. My Spectral DMA-260 amplifier specs are ±0.1 dB DC-150 KHz, ±1 dB DC-1 MHz, ±3 dB DC-1.8 MHz with distortion less than 0.015% from DC to 100 KHz, typically 0.009% @ 225 WRMS/8 ohms (static), and 8 Tone Cluster Test 20 KHz @ 500 Hz separation; 0.01% 8 ohms; 0.015% 4 ohms (dynamic). Based on these specs and my listening experience with the DAC 8 in my system Wide mode was the perfect choice. According to T+A Wide mode, "is the key to perfect frequency response and phase characteristics when used with power amplifiers with a broad-band output … The phase linearity and signal fidelity of the [Wide] circuit also has a perceptible effect in the audible range, and allows an open sound image with phenomenally clear positioning and ultra-lively dynamics." Sure some of those terms are marketing speak, but I'm a firm believer in wide bandwidth components after listening to them day-in day-out. Flipping back and forth between Normal and wide mode presents an audible difference in my system. The difference is not as major as the difference between digital filters, but it's definitely audible.

My Journey With The T+A DAC 8

I began my journey with the T+A DAC 8 several months ago when the whether here in Minnesota was in the 70s (F). Now it's 3 degrees outside and six inches of snow has accumulated in the last twelve hours. Needless to say I've spent a serious amount of time with the DAC 8. During this time I found two items that change the sound quality immensely. The first item is the digital interface or input and the second item is filter selection. The DAC 8 uses the Tenor TE8802L USB receiving chip that operates at all relevant PCM frequencies asynchronously. DACs with Tenor chips require drivers on both Windows and Mac operating systems. When listening via the USB interface connected to my CAPS v3 Carbon server running Windows 8 the sound was veiled at the top end, almost like the upper frequencies were absent. Listening to Elvis Costello's North album at both 44.1 and 88.2 via USB I thought something was missing. The sound wasn't involving. In other words I had a hard time staying focussed on the music. My favorite Nat King Cole album The Very Thought of You had a haze hanging over it and there was a lack of articulation in the lower frequencies of Nat's voice. For the most part the DAC 8 sounds fair to good via USB in my system. Seeking to bring out the best in this DAC I wanted to feed the other digital interfaces the cleanest possible source. That meant placing the Berkeley Audio Design Alpha USB between my PC and the DAC 8. I tried the AES/EBU input on the DAC and noticed an immediate improvement. The sound smoothed out a bit and the top frequencies came to life. The haze I noticed with the USB input was eliminated. Switching over to the Alpha USB's S/PDIF 110 ohm BNC output and the DAC 8's corresponding S/PDIF 110 ohm BNC input elevated the sound to yet another level, but I was still unsatisfied. Using the BNC input I heard more coherence overall in every piece of music. I listened to Tori Amos' Strange Little Girls album and the Kansas City Symphony at 24/176.4 quite a bit via the BNC interface. These two albums show a couple flaws in the DAC 8's sound quality but I couldn't put my finger on what was wrong. Readers should realize that the adjective "wrong" doesn't mean bad sound rather it means I thought I could pull more out of this DAC than I was getting at the time. Without several DACs in my listening room to compare I doubt I would consider the sound "wrong."

My last effort to improve the sound of the DAC 8 in my system lead me back to the user manual. Reading the specific sections about over sampling and filters I realized I'd made a foolish mistake many months ago. I meant to select the pure Bezier filter but instead selected the Bezier with IIR. The two selections are differentiated by a green light for the former and a red light for the latter. I grabbed the remote and switch the green light / pure Bezier interpolator on and was pleasantly surprised. It was like the invisible "thing" I couldn't put my finger on was gone and the sound was immediately very good. The Tori Amos track Real Men was brought to life with this game changer. The piano in this song was so much closer to a real sounding piano than anything I'd heard through the DAC 8 over the last several months. My body was at ease and my brain was no longer trying to fill in what I knew was missing with each track. This was never more evident than with Passacaglia from the Kansas City Symphony. Huge dynamic range and tight transients along with ever so soft bells were just a delight to relax and take-in. The BNC interface, pure Bezier interpolator, and Wide mode analog filter was THE combination that brought out the magic in the DAC 8. Everything was more involving with more detail and not a hint of boomy bass. More than anything the pure Bezier interpolator cleared up an otherwise muddy bass presence I heard with the Bezier IIR. Using this new found combination the only characteristic that still bugged me a bit was a slight lack of openness or airiness to the music. Ottmar Leibert's album One Guitar can sound open and airy with great decay, but I just couldn't squeeze that sonic attribute from the $3,250 T+A DAC 8.

I had found the perfect combination for the DAC 8 in my system. In order to cross my Ts and dot my Is I kept the pure Bezier interpolator and Wide mode enabled but switched back to the asynchronous USB interface. I really wanted this interface to perform as good as the others. However it wasn't meant to be. The pure Bezier helped but didn't bring the sound up to the level of the S/PDIF 110 ohm BNC interface.

Conclusion

The T+A DAC 8 is a very well designed and engineered DAC capable of very good sound. T+A has given each user the ability to fine tune the sound of the DAC to his/her own system and taste. Once time has been spent listening to the options, comparing the four digital filters, two analog reconstruction filter modes, and each of the interfaces anyone should be able to enjoy the DAC 8's very good sound in a myriad of different audio systems. Analog aficionados can groove along with the Bezier IIR filter while those of us born and raised on digital can squeeze a little extra out of our systems using the pure Bezier interpolator. I wish I would have discovered the best sonic traits of the DAC 8 much earlier in my review. Hopefully computer audiophiles can learn from my mistakes and enjoy this DAC from the first click of the mouse. I recommend the T+A DAC 8 without hesitation.

Manufacturer's Response

On behalf of Dynaudio North America, the distributor of T+A Elektroakustik products in the U.S.A. and Canada, as well as T+A, I would like to thank Chris Connaker for the excellent review of the T+A DAC 8. We truly appreciate the time, effort and consideration in terms of exposing this model and the T+A brand to the Computer Audiophile readership.

The DAC 8 is quite comprehensive and extremely flexible in terms of system configuration options, and while we are sorry to hear that it was a long road to find the winning combination, we are glad to read that: "Once I selected the pure Bezier interpolator all was right with the world. I’d found the magic I knew was inside the T+A DAC 8 and couldn’t have been happier."

One point that T+A wanted to convey to Computer Audiophile readers is that this is the first review of the DAC 8 to be published after the (October 26, 2012) release date of the Windows 8 operating system. To date, each of several previous published international product reviews, as well as the general consensus in the field, has been that the USB input of the DAC 8 (with Pure Bezier filter and in Wide mode) was the preferred input (and setup) as far as achieving the optimum sound quality out of this model. Your conclusion regarding the best-sounding filter being Pure Bezier with Wide mode being the best combination sonically collaborates the general consensus as well as T+A's own opinion in this regard. Where there is a discrepancy is in the conclusion that the USB input did not perform at the same level of the 110 ohm BNC input; the overwhelming consensus previously had been that the USB input offered the higher level of sonic performance over the still excellent performance of the other available inputs.

We have absolutely no questions regarding the fact that this was not your personal experience, but it did lead to a lot of head scratching. It just does not seem consistent with the factory consensus in this regard, one that was also later validated in the field by dealers, consumers and press alike who all pointed out the superior sound of the USB input in this model.

One possibility lies in the fact that this review is again the first DAC 8 review to have been completed after the release of Windows 8 (and using the corresponding new Windows 8 driver that was recently offered). To date, all relevant feedback was based on the DAC 8 being utilized via USB with a Mac OS, Linux or and earlier version of Windows. The T+A engineers are curious as to what the listening impressions via USB would be have been had an operating system other than Windows 8 been compared.

We understand that it is now too late to consider for the scope of an already published review, but perhaps this is something that can be arranged for comparison's sake in the near future or as a follow up? If anything to possibly verify if there may be a problem inherent in the new Windows 8 driver which may have prohibited the USB input of the DAC 8 to realize its full sonic potential - or to simply confirm your initial impressions. I assure you and your readers that T+A will be looking into this driver to further confirm if there indeed might be an issue with such. And for those who are using an operating system other than Windows 8, perhaps you can have higher expectations for the USB input and its sonic potential based on previous impressions throughout the world.

Thus we urge all Computer Audiophiles who may be interested in a high performance DAC to experience this model in his or her own system to see which settings and inputs would resonate most with their personal listening sensibilities. With the flexibility and overall value on offer, we are most confident that one will discover a winning combination that will have the DAC "singing beautifully" as Mr. Connaker did upon finding that magic combination.

Thanks again for the enlightening and insightful review, and for recommending the T+A DAC 8 "without hesitation". We truly believe that it is one of the finest sounding and most feature-laden DACs on the market, and surely one of the best options available anywhere under $5,000 retail. Thanks again for the enthusiastic recommendation as well as for your consideration.

Sincerely,

Dynaudio North America | Sales

Michael Manousselis

Director of Sales & Marketing

Product Information:

• Product - T+A Elektroakustik GmbH & Co. DAC 8
  
• Price - $3,250
  
• Product Page - Link
  
• User Manual - Link (PDF)
  
• Linux Information - Link (PDF)
  

Associated Music:

• Elvis Costello - North
  
• Tori Amos - Strange Little Girls
  
• Nat King Cole - The Very Thought Of You
  
• Ottmar Liebert - Not One, Not Two
  
• Kansas City Symphony | Michael Stern - Britten's Orchestra
  

Associated Equipment:

• Source: 15" MacBook Pro w/ Retina Display, C.A.P.S. v3 Carbon Server
  
• DAC: EMM Labs DAC2X, Berkeley Audio Design Alpha DAC Series 2
  
• Digital to Digital Converter: Berkeley Audio Design Alpha USB
  
• Preamp: Spectral Audio DMC-30SS Series 2
  
• Amplifier: Spectral Audio DMA-260
  
• Loudspeakers: TAD Labs CR1 Compact Reference
  
• Remote Control Software: JRemote, Apple Remote
  
• Remote Control Hardware: iPhone 5, iPad (3rd Generation)
  
• Playback Software Windows 7: J River Media Center 18
  
• Playback Software Mac OS X 10.8.2 : Audirvana Plus
  
• Cables: MIT Matrix HD 60 Bi-Wire Loudspeaker Cable, MIT Oracle Matrix 50 Analog Interconnects (RCA), ALO Audio AC6 Power Cables, Wire World Silver Starlight USB Cable, AudioQuest Diamond USB Cable
  
• Network: Cisco SG200-26 Switch, Baaske MI-1005 Ethernet Isolator, Micro Connectors Augmented Cat6A Ethernet Cable, Apple AirPort Extreme, Cisco RVS4000 Router, Cisco DPC3000 Docsis 3.0 cable modem, Comcast Extreme 105 Mbps Internet Service