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Transport vs DAC - Page 4

post #46 of 64
lol, another person who can't claim any experience. Scrith maybe your on to something, maybe your cheap ass computer transport is way more sophisticated than the ones high end companies are using. They probably don't have the technologies available to them that you do.
post #47 of 64
some gasoline for the flames :

http://www4.head-fi.org/forums/showthread.php?t=104545

I might add this one disclaimer-

I use my CDP both ways-to an external DAC and straight out of the line outs depending on if I am ready for serious music or just background noise.
My DAC is tubed so just to use it is not a good enough reason to fire it up if I am just listening to music so the house isn't dead quite when i'm alone (and nekked )
post #48 of 64
Quote:
lol, another person who can't claim any experience. Scrith maybe your on to something, maybe your cheap ass computer transport is way more sophisticated than the ones high end companies are using. They probably don't have the technologies available to them that you do.
easy man !

Do not get personal.That is against the rules and can only lead to going off topic.

thanks,

Rickmonsterator
post #49 of 64
Sorry im just really passionate about hi-fi
post #50 of 64
Quote:
Originally Posted by Scrith
And so, in my opinion, the best transport of all is a computer!
Please don't take this personally, but I seriously doubt if this is true.
Again, the biggest challenge of the transport, from what I have read, is not reading the bits correctly but sending out low jitter signals to the DAC via S/PDIF.
Inside the computer there are all sorts of interferences that could lead to degraded jitter performance. The weak power supply does not help either.
No doubt the computer is a great transport from the versatility/storage point of view, but in terms of sound quality, it is less than ideal.
post #51 of 64
I'm using a Benchmark DAC1 as my source, so hopefully that overcomes any jitter issues related to the computer? I have never seen an "error" light come on with the DAC1, at least.

Also, I'm using a toslink cable.

I am doubtful that there is a problem with the timing from my computer's E-Mu 1212M sound card, but I guess I'll have to try comparing it to the output of a CD player just to be sure. By the way, my PC's power supply is a PC Power and Cooling Turbo-510, which is generally regarded as the best computer power supply you can buy. I monitor the various voltages coming out of it and they have always looked very good (much better than my old Enermax and Antec power supplies did).
post #52 of 64
just as an add guys.

if you check the Wavelength Audio website and specifically the Cosecant DAC page there is a powerful argument made for the computer to DAC via the USB connection being superior to any CD Transport and DAC combination in the jitter department because the USB connection is inherently jitter free !

i suggest any who have an interest in these things check it out
post #53 of 64
Quote:
Originally Posted by rickcr42
just as an add guys.

if you check the Wavelength Audio website and specifically the Cosecant DAC page there is a powerful argument made for the computer to DAC via the USB connection being superior to any CD Transport and DAC combination in the jitter department because the USB connection is inherently jitter free !

i suggest any who have an interest in these things check it out
Checked the website od Wavelength audio. I can't see what is the basis for their claim that USB interface is jitter free. Using google, I found that many USB DACs use PLL to reduce jitter. This clearly indicates that USB interface is NOT inherently jitter free. Maybe Wavelength audio found some very clever way to reduce or even eliminate jitter. But their oversimplified claim is very unconvincing to me. To me it reads more like marketing hype.
Some other head-fiers who have a much better understanding of USB jitter have discussed Wavelegth Audio's claim in this thread:
http://www6.head-fi.org/forums/showthread.php?t=74248
post #54 of 64
I remember reading about an interesting demonstration of CD transport
sensitivity a while back, can't remember the specifics though.
But it involved having an opera singer sing a particular note AT a cd player
whilst it was playing and when the singer hit a specific frequency the player ceased to play!
If I recollect , this was due to the singer having reached the resonance frequency of the laser/coil assembly and vibrating it to the point where
the servo correction could no longer correct the errors generated by its
elevated levels of movement.
If the above was the case then it does suggest that a good mechanical design is of some importance.

Plenty of information/discussion of transports,digital interfaces etc can be
found in the digital section of:

http://www.diyaudio.com/


Setmenu
post #55 of 64
Quote:
Originally Posted by setmenu
If I recollect , this was due to the singer having reached the resonance frequency of the laser/coil assembly and vibrating it to the point where
the servo correction could no longer correct the errors generated by its
elevated levels of movement.
If the above was the case then it does suggest that a good mechanical design is of some importance.
Interesting!

I was reading a back issue of Stereophile last night where they had written about an older Krell player with a clear lucite 'window' so you could see the CD spinning around. The player was being photographed at a trade show, and every time a flash went off, the CD skipped!
post #56 of 64
Quote:
Originally Posted by rickcr42
the USB connection is inherently jitter free
This is a little misleading, because as I understand it, usb (like most data transmission protocols) is asynchronous, meaning "clock-free". On one hand, you could say its jitter-free because there is, in fact, no clock at all. On the other hand, since the data transmitted across a usb line isn't clocked, it doesn't necessarily transfer at a regular rate. It may send nothing one moment, and in the next send data even "faster" than the equivalent of real time. Jitter in CD transports is measured in picoseconds (trillionths of a second), jitter over a usb line would need to be measured in milliseconds (thousandths of a second) if it even made sense to measure it...not even good enough to get a lock on a typical DAC.

So is USB a bad idea for audio?

Not necessarily. USB jitter performance depends on the receiving circuitry (the PLLs that Ferbose mentioned in his post, among other things). I'm no engineer, so I don't really know any more than that, however, I found an article that may explain it:

http://www.planetanalog.com/showArti...cleID=12801995

I haven't read it yet (it's quite long), but it's written by an engineer at Burr-Brown who worked on the PCM2702, a USB controller chip with a built-in DAC. If no one beats me to it, I'll post a nutshell version after I read it.
post #57 of 64
heh,I posted the same link in DIY where i though it fit a little better but it is also on topic here so good call man



The USB connection is potentially a lot better because it totally eliminates the spdif interface where a lot of the jitter comes from-

the SPDIF transmitter>75 ohm Coax or Optical light pulse cable>SPDIF Receiver digital signal path
post #58 of 64
Quote:
Originally Posted by clarke68
USB jitter performance depends on the receiving circuitry (the PLLs that Ferbose mentioned in his post, among other things). I'm no engineer, so I don't really know any more than that, however, I found an article that may explain it:

http://www.planetanalog.com/showArti...cleID=12801995

I haven't read it yet (it's quite long), but it's written by an engineer at Burr-Brown who worked on the PCM2702, a USB controller chip with a built-in DAC. If no one beats me to it, I'll post a nutshell version after I read it.
Thanks for the interesting link! Exactly the kind of thing I'm interested in learning more about...

Jeremy
post #59 of 64
Quote:
Originally Posted by clarke68
I haven't read it yet (it's quite long), but it's written by an engineer at Burr-Brown who worked on the PCM2702, a USB controller chip with a built-in DAC. If no one beats me to it, I'll post a nutshell version after I read it.
Okay, I'm only half-way through, but I've read enough to write that, in a nutshell:

No way is USB inherently jitter-free.

Not that its terrible, it's problems can be overcome with highly skilled engineering and/or expensive parts. Overall, that makes it no better or worse than s/pdif, whose problems can also be overcome with highly skilled engineering and/or expensive parts.

Quote:
Originally Posted by rickcr42
The USB connection is potentially a lot better because it totally eliminates the spdif interface where a lot of the jitter comes from
Perhaps I haven't reached that part of the article yet, but my take at this point is yes...potentially. An expensive, well engineered usb solution could be a lot better than a cheap, poorly engineered s/pdif solution.

It is true that s/pdif introduces a lot of jitter into the signal. USB can be used to eliminate it, but jitter comes from a lot of different places, and usb definitely has its own limitations and challenges.

There's just no such thing as a free lunch, there is no magic bullet (no data transfer protocol, file format, up/over/non-sampling, or whatever) that's going to solve all of digital audio's problems. Like most problems, this will be solved with a lot of two things: time and money.
post #60 of 64
Yep, the only solution I see to the problem is a LARGE buffer of some sort, the necessary digital components to feed a DAC regular data from this/these buffer(s), and a high-quality clock located on the device to provide a "clean" clocking source.

Not being an electrical engineer, I can't say how feasible it is to do this and be able to produce a hi-fi analog signal. But it sounds like a good idea!!!

Does anyone know of devices on the market that do this?

I want one!

Jeremy
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