how tell if you're bit perfect?

[thomaspf]

@Don Quichotte

That's quite possible. That is actually how an asynchronous sample rate converter works.

You have two separate clock domains. The inherent clock in the incoming digital signal and and independent local clock. The sample rate converter is clocked by the local clock domain and just receives whatever samples the externally clocked digital link will provide. At the end of a unit interval it will translate this potentially arbitrary number of samples into to a fixed set of samples with "different" values and hand those to the converter.

Even if there is zero jitter in the input but a certain drift in the frequency then the likely outcome is that all samples are different.

In order to avoid this problem many professional sound cards come with a word clock input that allows you to slave the digital output to the external clock in the DAC.

Cheers

Thomas

 

[Don Quichotte]

So this is the reason why the Benchmark measurements seem to confirm their claimed 100% jitter immunity: because they are actually measuring the presence of jitter induced sidebands - eliminated by the reclocking of the input data - while this data is actually slightly altered in the process (an alteration that is not depicted by the technical measurements)! This would explain why some people can hear a difference between various transports when using a Benchmark, a Bel Canto or other Dacs with similar reclocking technology!

I'm more than surprised, I'm kinda shocked! Are you really sure this is how it actually happens?

Is there any external Dac like these mentioned above that can output it's own clock for slaving the transport? Or this is solely a feature of some soundcards and perhaps some much more expensive Dacs? My Cambridge CD player sems to have a so called "clock in / upgrade" input, perhaps it's possible to slave it to an external Dac...

One more question: this phenomenon also takes place when connecting a USB Dac like the Apogee to a computer? Or is there any other sonic advantage of this kind of a setup (maybe this last one is a topic for a different thread?!) ?

 

[jefemeister]

Quote:

Originally Posted by Don Quichotte Is there any external Dac like these mentioned above that can output it's own clock for slaving the transport? Or this is solely a feature of some soundcards and perhaps some much more expensive Dacs? My Cambridge CD player sems to have a so called "clock in / upgrade" input, perhaps it's possible to slave it to an external Dac...

Hooray! The truth is starting to come out. The DAC1 is not as "jitter immune" as they claim. What they're doing is embedding the jitter error into the data. To answer your question: to the best of my knowledge Wadia is the only company that slaves the transport to the DAC's clock nd it is the only theoretically 100% perfect way to eliminate jitter. Some products have a clock input on the DAC, but that system involves locking the two clocks together using a PLL which has a host of problems of its own.

 

[thomaspf]

An asynchronous smaple rate converter makes you imune to jitter but at the expense of the impact described above. Whether this is detrimental to the sound is of course an interesting question since the sample rate conversion is executed with very high fidelity. I leave that dispute to others with better ears....

Many professional DACs support a local clock without a sample rate converter. Wadia is "in"-famous for claiming that bicubic splines for upsampling sound more musical.... so I don't know what they do. Here is a very incomplete list from the top of my head with DACs that have a master clock output.

DCS Delius, Elgar, 954, 955
Universal audio 2192
Apogee Rosetta 200 & 800
Meitner DAC6e, DCC2

If you own a sound card with digital input you can usually select that as the clock source and slave your card to a DAC like the UA-2192 which seem to have a good price performance ratio.

Cheers

Thomas

 

[Glassman]

just to complete the picture, I'll ask: what happens to the data fed to the D/A converter? are they converted bit by bit as they come? certainly not! they undergo synchroneous resampling / oversampling, the DAC won't see the original bits..

however, it is vital to have bit perfect data transmission up to the oversampling filter..

the thing with asynchroneous resamplers embeding incomming jitter into the outputted data, that's correct, however the jitter / phase noise will occur at frequencies bellow 1Hz, which is something one shouldn't be able to spot under any circumstances, that is.. so I'd call them jitter shapers