Does anyone know the ID / OD dimensions of the DC plug socket of the Teralink-X and Teralink-X2? I need to know to order an appropriate regulated PSU.
post #586 of 1712
1/22/10 at 1:51pm
I was also curious to see if there is a difference between transports so I made the test 2 or 3 months ago but the test were inconclusive and surprising so I don't believe I have mentioned it before.
For my test, I used the EMU 0404 USB as a recording device. Since I found that it had very low measured distortions, I thought I could see the difference in the output of the dac19mk3 in the THD or IMD graphs.
I tried the Teralink and the Musiland and they gave me similar results. However, when I salved the digital input of the EMU to the musiland (using a cheap toslink cable) the SNR of the dac19mk3 improved by 3db but the THD and IMD graphs didn't change.
My conclusion is that trying to assess the (jitter) performance of those usb to spdif converters looking at an RMAA graph with the help of consumer grade sound card is probably pointless.
In my opinion, to make worthwile measurements, the tester should have a world class ADC with a known ultra stable clock and not just a clock that is advertised being "ultra-low jitter". To make definitve conclusions about jitter, one should use something like Audio Precision 2 ... if the ADC is inferior (in the time or frequency domain) to the DAC it is measuring the results are probably skewed.
Anyway, I have had a few e-mail exchanges recently with Kingwa (from Audio-gd) who told me that jitter measurements do not tell you the whole story about the quality of a transport. There are other parameters (transformers, clock phase noise, power pulse effect to the signal, ...) that will also impact the sound of the DAC. I highly doubt that the measurements done by RMAA will let anyone correctly assess the whole performance of a transport.
This is indeed the reason you have to use rmaa to measure not a digital loop, but analog loop. Using some good ADC you record the analog out of the dac fed with various digital transports. You should try first with some reference quality transport to see what should be the result of the dac working as it should (but this data should be provided by the manufacturer). Then you should try the another transports. All the factors you listed are included in this test, cause you are not measuring jitter but the final result. If there is a difference in quality of the transports, for whatever reason, you should see a difference in the analog output of the dac you are recording, I think this is obvious.
If there are sonic differences they should be visible in those recordings.
There are a lot of reasons that make what you are asking very difficult to realize :
First, a good DAC means using something at least as good as the Lynx Aurora or Prism Dream AD-2. Not many head-fiers have that lying around I believe.
Second, the use of a reference transport. How to assess that a transport is a reference class product ? Is it by looking at its specs, digital measurements ? I guess that to be on the safe side, someone should you a CEC cd transport or other well known high end transports.
Third, the DAC itself. We have to assume that the only significant distortion that will show up will be jitter induced. So the perfect dac for this kind of test would have vanishingly low level of distortions but would still be very sensitive to the jitter/transport.
Fourth, we are assuming that the digital cables do not interact with signal being transmitted. If you read what Dan Lavry wrote about jitter in cables and impedance matching, you will realize that you won't be measuring the transport but also the whole chain (digital cables, connectors, ...)
Last, we are assuming that if there is a sonic difference it will show up on the RMAA test and that we would be able to interpret it. This hasn't been the case in my opinion. I have tried very different sounding opamps for example but nothing significant showed on RMAA tests. If RMAA held the truth, I should be listening to the EMU 0404 usb which has vanishingly low level of THD, SNR, and IMD. Since the highest harmonic (the third) is at -110 db so I don't believe I should hear any kind of distortion. However, whenever I play violin or piano recordings through it, it sounds digitized and nothing like the real thing. It is not even a subtle difference but a gross difference. On the other hand, I have listened to dacs that didn't measure as good but that outperformed the EMU 0404 usb in sound quality.
In my opinion, we still have to rely on our ears to evaluate those things because at the end of the day we wont be listening to our systems with a distortion graph but with our ears.
However, if you are still curious about how those units measure, I had already done some research and I included the results I have found in my review (first post). To save you time I copied below an extract of the paragraph :
While jitter measurements should be interpreted with great care (different results with different equipment and test protocol), it is sometimes a nice tool to make jitter comparisons in the same group of transports done with the same equipment.
Here you can find jitter measurements of the m2tech, a LynxTwo pci sound card, a Nagra DII and a Marantz CD player. In that test the m2tech was slightly better than the LynxTwo which is a professional grade PCI card, and better than the Nagra and Marantz cd player.
On a stereophile test, there were measurements of the EMU 0404 usb and other converters. The EMU had the worst jitter of the bench, and its jitter was 8 times that of the one measured with the m2tech (Granted the tests were done with different measuring equipment).
We are talking about digital transports, not about the sound the dac produces. To me is pointless if the dac measures 50 or 100, I said use a source sensitive dac. If is DIGITAL SIGNAL QUALITY what we are talking about, the problem is not HOW the dac sounds, but WHAT DATA arrives to dac. If there are errors of any kind, jitter or whatever you listed, you will see a degradation in dac performance, or at least a DIFFERENCE. I think the only thing would be have a GOOD ADC, cable is not important ok? Use a good belden cable and youre ok.
When I see people saying things like "rely on our ears" you can understand why 90% of reviews on this forum are totally lacking of trustworthness.
I am still convinced you can hear more difference in two listenings depending on your mood more than real sound difference.
So you were suggesting to measure those usb to spdif converters (with a DAC) just for the sake of measuring ? Not because it would affect the sound which would ultimately come out of the DAC (and ultimately from your headphones) ?
Anyway, this is a pointless debate, I won't comment on it any further. I just wanted to save time for people but if anyone feels like they want to spend a lot of time measuring those usb to spdif converters to look at unreliable graphs, please feel free to do so.
And finally, if you feel that "90% of reviews on this forum are totally lacking of trustworthness.", you should write your own reviews as it would be more constructive and instructive for everybody instead of just criticizing other people reviews and comments.
When I say they're laking of trustworthness I am not saying this is on purposal, I used to think these reviews were useful but I am changing my mind, and I'll explain why:
usually when you have a lot of informations about something, but not all this information is reliable, by comparing and analyzing it you can have an approximation of what is the reality. Some reviewers could be completely influenced, others could be more objective, some inexperienced, some experienced etc. but in the end something valid will come out.
Actually this doesn't happen in the audio field. This mostly because, in my opinion, people say things that aren't true, believing they are. In the end, you will find, very very often, people saying "I think X is better than Y for A reason" and elsewhere "I think Y is better than X for B reason".
The principal cause, for the lack of objective benchmarks, data, real information of what counts and what doesn't.
Just my opinion.