Pacific.Digital

With good playback gear downstream of the DAC, polarity reversal is pretty obvious. The recording sounds flat, obtunded, a little lifeless. Switch the polarity, things get better instantly. Sure, if you're listening to recordings with "fix it in the mix" as the prime directive, they'll sound mediocre either way. But carefully-done work (Proprius, Reference Recordings, Sheffield) and so forth is good reference material for those who'd like to learn about how polarity reversal affects the sound.

Demian is certainly correct re the low frequencies being where most of the phase noise accumulates. Let's see if we can get MSB to comment. The engineer doing the OXCO design certainly knows what he is doing.

So how did you get the FireWire to work with your DAC? In my case, it would work fine on Vista, with a Qosmio laptop, but not with any of my Windows 7 laptops from HP...

My system, used for the review in PFO, is very simple: Computer source, DAC and amps. This eliminates quite a few of the variables. My observations on the Weiss DAC 202 are based upon hundreds of hours of use, and comparison with DACs way more expensive ($30-70K) as well as somewhat less expensive ($5K). The associated gear included the Pass XA200.5, as mentioned in the article, and Wilson Sashas. The system is very simple. Regarding the use of an external clock, why this should make any difference is not at all clear to me or others who are much better informed on the engineering level, but it certainly does. The DAC sounds best with the Grimm clock, especially at 44 kHz. FireWire was definitely not the best-sounding input, at least with my computers. The outstanding virtue of the product is its flexibility with respect to integration with a complex recording studio environment; right behind it are the excellent ergonomics, appearance and ability to match the gain structure of the rest of one's system. The sound quality is good overall, but one should give a careful listen to similarly-priced competing products, some of which are quite a bit newer in design.

Your interesting question addresses one of the core, critical areas of everything relating to digital and computer audio. There is an informative white paper on this subject at the Grimm Audio www.grimmaudio.com Web site. http://grimmaudio.com/whitepapers/Picoseconds%20or%20ppm.pdf Basically, the accuracy of a clock, meaning what time is it, in, say, 100 years, is actually not very important. What really matters is the short-term stability of the clock, generally described as phase noise. For high-quality clocks, the phase noise over a particulat bandwidth, say 1 Hz to 100 kHz, will be in picoseconds, possibly femtoseconds. Jitter is another way of expressive phase noise. Very low frequency phase noise, from 0.1 to 1 Hz, seems to be very important for realism, presence and soundstaging. Most USB-S/PDIF interfaces don't even have published phase noise or jitter specs, which often relates to the fact that their performance in this regard is poor. Rad the reviews in Stereophile and 6moons. Often the designers don't have the equipment or technical knowledge to make sure measurements in the first place. Until quite recently, good phase noise analyzers cost from $40 to $100K and up. Using an excellent external reference clock may improve the performance of even high-quality DACs which have a word clock input. In addition to the Grimm CC-1, the Black Lion Audio Micro Clock MK2 has very good phase noise measurements. So you're asking exactly the correct question: Why are clocks important, and how does one evaluate them? This is a beginning. If you check Wikipedia, there are some good discussions about phase noise and jitter.

Demian, Here's two for you to try out, along with the C code which should allow you to make your own files.. They're from WakiBaki at DIY Audio... Jitter2 is 48/24 and Jitter3 is 44/24. http://www.diyaudio.com/forums/digital-source/183110-jitter-test-signal-j-test-signal-matlab-3.html Should produce 1 minute of 24 bit JTEST... http://www.ne.jp/asahi/fa/efu/soft/ws/WS140.ZIP for a 44/16

@tpaxadpom... thanks so much. A 44.1kHz/24 bit would be great to start, and then a 176 and 192 thereafter. Some devices are highly data pattern sensitive, others seem to be immune. We have the APx515 which will play .WAV, but it doesn't seem to have the ability go create arbitrary data files.

Does anyone have a 24 bit JTEST .wav they'd be willing to share? Some are available online but their provenance is a bit murky.

@SLM The Berkely Audio Design DAC is one of the best on the market. To get maximum performance from it, you'll need to "feed" it with S/PDIF with very low jitter and phase noise. BAD has their own USB interface now, which is of course top-notch. Some of the alternatives mentioned here are nowhere near the same quality, although they're less expensive, which, of course, is a consideration. The output of the Mac Mini has very high jitter, according to published measurements, so the USB-S/PDIF interface needs to be quite robust. Take a look at the Audiophilleo2 ($495) which is their basic model, which should do the trick with high-end DAC. The jitter is about 2.6 picoseconds RMS from 10 Hz to 100 kHz. The Audiophilleo plugs, mechanically, directly on the BAD DAC, which not only improves performance, but also eliminates the cost of an S/PDIF cable.

Is it possible that you could get TOSLINK by purchasing a docking station? It also might have a better coaxial output than the laptop itself. Surpised that a high-spec Toshiba doesn't have TOSLINK. For $1395, the Bel Canto 1.5 is quite nice. The Weiss DAC 202 is lovely as well, but of course more expensive.

@Magichord... just went through this while reviewing the Bel Canto 1.5. Basically the TOSLINK works very well on my Toshiba Qosmio, although it seems to be limited to 96 kHz. Tne Qosmio is their high-end multimedia product, and has a separate TOSLINK output. Other laptops have the TOSLINK piggy-packed on one of the headphone jacks, along the lines of the coaxial S/PDIF on your Satellite. The lousy dynamics from the S/PDIF may reflect the limitations of the receiver you used, but they are also compatible with the very high levels of jitter that most S/SPIF output from laptops seem to have. Another consideration is that with the coaxial connection, all the power supply crud from the laptop may be getting into the receiver, same symptoms. The TOSLINK offers possibly lower jitter, and for sure, it isolates the receiver quite well from noise in the laptop. A high-quality USB DAC will work just as well, but at the lower end of the range, TOSLINK may work better, depending on the type of USB interface technology used. Asynchronous USB, other things being equal, should offer better performance than older USB control protocols. BTW be sure to use a glass fiber TOSLINK cable. Excellent products are available from WireWorld (including a miniature plug that some computers will need) and also AudioQuest. If you have a high quality receiver available, or are thinking of buying one, you might be better off to use a very high quality USB-S/PDIF converter between it and the computer, and not worry about the USB DAC. In other words, put your money into a better receiver, especially if you want to do multichannel audio (playing back movies from the laptop, etc.). Some receivers has USB ports these days, which would make life even easier.