Hi Cavan and Chris:

I was just about to ask almost the same question.

I have a few facts, but still wondering which connection type to use.

1.) I downloaded a few albums from Linn to play on my office system. I use a Macbook Pro, and connect to my Bryston B100 DA integrated amplifier with a Toslink cable. So far most of the files have been 24/88.2, one 24/96 album, and one 24/192 track (downloaded from 2L). I must say, the sound quality and detail was far better than I expected, and can see why computer audio can be so addictive.

The 24/192 track would not play at first, then sounded horrible. Of course I know why. First, that size of file requires a cable with a 10MHz bandwidth, and my high end plastic cable is rated at 6MHz. Second, the internal Bryston DAC only accepts files up to 24/96.

So the problem was the cable and the DAC.

2.) I was recently made aware of an additional problem with optical connections. Toshiba makes enough different TOSLINK Optical Modules to fill a bucket. It depends on the use of the component as to which module is selected. Since most consumer TOSLINK cables are limited to a 5 or 6 MHz. bandwidth, why use a module that exceeds that rate of transmission or reception. I'm not sure how accurate this is, but I am told that the modules used for consumer audio are different than the modules for pro audio components. In addition, I have no idea which modules are used on computers. Just check out this PDF file from Toshiba:
http://www.toshiba.com/taec/components/ProdLineGuide/toslink.pdf

Question: For high sample rate files (above 24/96) you can change to one of the new Quartz glass cables. However, when it comes to modules, how do we know if any of the 24/192 files can even be played with TOSLINK ?

3.) Of course the above leads me directly to the DACs. Not all the DACs mentioned on this forum process the input of 24/192.

Questions: However, for the units that do, will their TOSLINK module accept those file rates? Would the manufacturer be able to answer that question? Which computers will transmit the higher sample rate files? Then again, the optical modules may not be a factor, just the cable.

4.) Let us assume that the optical modules can be a factor. That leaves us with SPDIF/Coax, USB, Fire Wire, AES, and BADA (on the Berkeley), and now talk of adding Ethernet inputs on DACs. Can the situation become more complex?

More Questions:

USB: Just since I joined this forum USB has started to appear on DACs. The only limitation is the length of cable. However, I still do not see any specs on which version of USB. It must be at least 1.1, or does the connection include 2, or possibly the new version 3? Just asking, because after the RMAF the discussions about DAC makers dropping Fire Wire in favor of USB was because IEEE was slow releasing the new versions, but USB had released their version first. Seems like a lame answer if the new USB release is not being employed.

Fire Wire: Well it seems Fire Wire has been eliminated from a number of future DACs. That is the understanding I receive from discussions on this forum. But who really knows? Perhaps we are all making too many assumptions?

AES: I have heard conflicting stories about AES/EBU digital cable using XLR connections. Some say it can be used up to 100 meters, other say 10 meters. It would be be really accommodating for my home system because my computer is placed 28 feet away from my audio components (which means I would need to run cables a good 50' long). So, can I run AES cable from a DAC to my pre amplifier with that length without any analog signal problems?

5.) I just purchased a new Mac Pro for my home and was planning on using the Lynx AES16e sound card. Now I have a foolish question: why am I purchasing a sound card with DB 25 pin I/O connectors when the DAC digital input is only (what I assume to be) a single three pin XLR connection? Oh, and just where would I obtain such a cable?

Thanks for your help,

Daphne

First USB:

There are a number of different implementations ranging from custom, requiring programming and S/W drivers, to chips from TI that are plug-and-play. As you would expect, the more custom it gets, the better it sounds. Most manufacturers for their first try used the PCM270X parts from TI, which sound quite bad, even with low-jitter clocks driving them. Some are changing to the TAS1020, which requires some programming, and others are using completely custom implementations with embedded processors. Most high-end audio USB interfaces are limited to 24/96, but this wil change to 24/192 in 2009. These programmed interfaces can sound excellent, but only if the implementation is good and the clock used has low jitter. It's like all other designs in audio circuits: Just choosing good parts does not guarantee good sound quality.

As for long cables:

AES, Toslink and even USB cables should be as short as possible unless a good reclocker is used after them. For 28 to 50 foot runs I would recommend WiFi using the Sonos or AirPort Express (iTunes). These devices have high levels of jitter, so if you want them to compete with your good transport/CDP, then they will need reclocking. The data itself is delivered bit-perfect and error-free with these networked devices. It is only the jitter that needs to be addressed.

In order to have accurately reproduced digital audio, the D/A converter needs two things:

1) accurate data ( this is easy - errors are rare)
2) accurate timing - this is the difficult one

Jitter, which is inaccuracies in timing, can be reduced by several methods, including asynchronous reclocking, synchronous reclocking, ASRC or Asynchronous Sample Rate Conversion. Each of these has a different level of effectiveness, the synchronous reclocking being the most effective.

Steve N.
Empirical Audio

Audibility of jitter is like audibility of different cables. Most self-proclaimed audiophiles systems are not good enough to hear the benefits of either, so there will always be non-believers. In fact, most reviewers systems are not good enough either, even some of the editors of HIFI magazines!!

Most systems have high levels of sibilance and noise, so the benefits of removing jitter are not as great. In most systems though I can hear the difference with the right track. This was demonstrated recently at RMAF in a room where the turntable and the CD player sounded identical. The preamp was "homogenizing" the sound by adding noise and distortion.

This is why I'm really careful about who I send gear to for reviewing.

Steve N.
Empirical Audio

Hi Steelman:

Thanks for the information on optical and USB connections.

By the way, I am familiar with Lifatec and use several of their high quality plastic cables. They are very reasonably priced, well made, thin, and light weight, which makes a big difference when connecting to a Macbook Pro. My only complaint is the TOSLINK mini jack used by Apple is the number one least reliable optical connection made. I have no idea why the consumer A/V and computer industries use such poor connectors. A good 90% of the optical fiber market (the telecommunications, instrumentation, and medical industries) all use a variety of locking connectors.

Regarding the Lifatec claim of 40MHz bandwidth. I believe that test was done with an industrial transmitter and receiver, not the type of low level red LED used with A/V TOSLINK applications. Audio optical cables is a small fraction of Lifatec's business. For consumer audio the bandwidth of most plastic cables will max out around 5MHz to 6MHz, but Lifatec uses the very best plastic fibers made and for shorter lengths their bandwidth is definitely more.

"I have found that the technical specifications relating to digital audio inputs and outputs is difficult to unearth. I think contacting the manufacturer is a good idea."

So true Steelman! I keep thinking about the frustration of assembling all the components only to discover that the data is being shaved, or creating major jitter, due to the connections I select. You could say I'm just performing proper due diligence prior to rushing out and making purchases, but once I started to examine the technical specifications I found a void. Naturally I started to ask questions only to discover there are few answers beyond what I already know.

"Last week I had a question on the B100-SST (ironically!) and James Tanner from Bryston provided a pretty detailed response in record time, so you might want to drop him a line regarding your Bryston:"

I saw your post about Bryston, then had to work. By the time I had a chance to respond, I was truly surprised to see a response from Bryston's, James Tanner. Come on, Steelman, what are the odds of asking a simple question and receiving a direct, concise reply from the manufacturer? The only thing I can add is, if you are looking for an integrated amp with average power you cannot go wrong with the B100 or the B100DA. I am currently looking at DACs for my home system and seriously considering the BDA-1 as a possibility.

Daphne

Ha! nonsensical and high-end audio in the same context? No, it can't be true.

I like the post mpmct.