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Do Transports Matter--or are bitses bitses?


The Monkey

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Off-topic, bye bye regal.

Excellent news, because we all could see that was a train wreck waiting to happen. I'm all about preventative maintenance.

could i get it in burl walnut?

If you can keep it under your hat. I don't want people thinkin' I'm Burger King.

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I happened to be privy to Regal's second post, where he goes on to state that he tested different transports in weightlessness, in his Brothers space shuttle. In zero gravity he could detect a very minor difference in the Uranium cased unit that his Father in law owns, over the Platinum series that he borrowed from Howard Hughes (yes, he's still alive).

I always viewed you more as Green Burrito.

:D In more ways than one. I'll come back to haunt you in a few hours too. :P

Edited by swt61
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I never had perfect headphones so I never investigated my transports too much. I try to make sure that they are bit perfect and that's about it. The problem is that the sound differences are very, very small if there are some at all. So to me, transports do not matter too much, a good working sound card is enough for me.

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I built these two DACs. Both use a CS8416 receiver, a WM8741 DAC, and the same output stage. One uses a Wolfson receiver between the 8416 and the 8741 to reduce jitter, the other an ASRC. The ASRC is upsampling which may be a bigger difference than the jitter, so the test is not quite fair. I'll need to retest with a different clock speed to equal that out. But, the jitter is one of two main variables, so take it as you will.

THD and frequency response differences shown below. Note that there is 0 feedback in these designs (not even source follower local fedback), so THD is higher than for an opamp output stage, but still very good and the sort of distortion that generally does not sound bad.

8804 has (very slightly) higher 2nd harmonics, ASRC has higher everything else. 8804 has higher noise floor which I can't explain. (The 60Hz/120Hz/180Hz/... bumps are an artifact of the soundcard.) The frequency response for the 8804 looks slightly better, too.

I think the ASRC sounds better.

Colin has heard both so he may be able to comment further.

8804 THD

IMG]http://www.ecpaudio.com/images/8804_thd.png

ASRC THD

IMG]http://www.ecpaudio.com/images/asrc_thd.png

8804 FR

IMG]http://www.ecpaudio.com/images/8804_fr.png

ASRC FR

IMG]http://www.ecpaudio.com/images/asrc_fr.png

I did hear these, and when I was listening, did not know which was which. I 0.thought maybe I slightly preferred the one with the ASRC, felt it was just a bit smoother. It was the kind of thing where I wasn't sure if I was really hearing the difference or what, but they were VERY close either way. Liked both though, real nice sounding DACs.

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I would also say choice of transport can matter if you are using the coaxial connection with certain DACs. Since the receiving circuit becomes part of the S/PDIF communication circuit, the DAC implementation in conjunction with the transport implementation could influence the S/PDIF signal fidelity. Also, noise or strangeness on the shield or the signal could be a problem if a DAC wasn't using an isolation input transformer or the shield noise carried into other parts of the DAC.

In other words, I'm saying transports could matter more with some DACs than with others for reasons besides jitter or a non-bit-perfect implementation.

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I would also say choice of transport can matter if you are using the coaxial connection with certain DACs. Since the receiving circuit becomes part of the S/PDIF communication circuit, the DAC implementation in conjunction with the transport implementation could influence the S/PDIF signal fidelity. Also, noise or strangeness on the shield or the signal could be a problem if a DAC wasn't using an isolation input transformer or the shield noise carried into other parts of the DAC.

In other words, I'm saying transports could matter more with some DACs than with others for reasons besides jitter or a non-bit-perfect implementation.

Great point. I thought that the effect due to this interaction was usually considered jitter too or at least that's what the pro equipment manuals call it when they warn you to use good cables for this etc.

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Happy New Year, Wes! What transports do you like/not like?

It's probably the lazy engineer in me, but I prefer to avoid potential problems completely so I don't have to worry about things. At home I am pretty much using computer-based streaming systems since that virtually guarantees no read errors (storage error detection and correction being more reliable than redbook) after a good rip. And optical for gear and S/PDIF circuit isolation. But that also depends on knowing that the DAC won't care about reasonable S/PDIF jitter.

Great point. I thought that the effect due to this interaction was usually considered jitter too or at least that's what the pro equipment manuals call it when they warn you to use good cables for this etc.

They're probably referring to the effect reflections can have. I guess it would be fair to call that jitter too, since the effect on the signal can be similar. But I'd hesitate to group it that way since that isn't how I think of things. Perhaps just a difference in background.

Reflections was indeed one of the things I was thinking of, but even with a perfect reflection-free circuit there could be other yucky things being transmitted or picked up from the environment and those could also have an influence.

For example, the test lab at my manufacturing house is full of all sorts of test equipment. To perform accurate tests with the DAC cover off, we had to test after hours with all the other stuff powered off. Likewise, during regular business hours the coaxial S/PDIF cable and measurement cables would pick up noise. UL testing is done in a shielded environment (even the transport is outside the "box" and attached with a long cable IIRC), since FCC Part 15 Subpart B only says gear can't emit radiation and doesn't care if gear will reject radiation. So you have to make sure of the latter yourself.

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Just for fun, same SPDIF transport (optical input to Audio Alchemy DTI v2.0, BNC out), same 75ohm BNC 'T' adapter with the middle leg into my Tek 7704a with 7a16a module, and same Blue Jeans BNC cable output into a 75ohm BNC terminator. The variable here is the cable from the DTI to the 'T', first case is another BJC BNC-BNC.

bjcbnc.jpg?t=1294529619

Second is a standard RCA cable, I think it was an AR brand one, with RCA-BNC adapters on both ends.

rcaadapter.jpg?t=1294529620

Did this quite a while ago, can't remember for sure but something is telling me the time scale might have been showing up wrong on the screen. Regardless, it was the same for both tests.

Edited by cetoole
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  • 1 month later...

Heck no. I almost bought it the first time around out of curiosity, but they couldn't give me an orange one, so I said screw it.

The newest one is crazy-priced! You could get a more-than-decent DAC over THIS: it's just a USB-to-BNC converter. I don't care how exact it is, the price is just exorbitant for what it does. If it was also a DAC then yea...

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Paying that much for casework in a USB transport, you kinda would have to get a custom computer case to match. I can't think of any off-the-shelf towers that are blingy enough. I like the silver Lian Lis, but even those would not be shiny enough to convey your general disregard for money. Maybe just stick a few bottles of Cristal on top?

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