DIYHiFi.org

Hmmm, it works for me all the time...
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It may depend on the usb bridge. I have had problems with the VIA 4 in 1 system. Just the other day, my processor went into a loop, consuming near 100% resources. Discovered much later that it wsa a usb extender doing its tricks.

May be I am particul;ar, but I am used to 100% functionality. I get it from my hifi boxes; I don't from computer audio and it is often not clear what a piecec of software is doing.

Sweep of PCM2706 MCLK output, JTEST, USB1.1 & Self Powered by a Low Noise external PSU.

If you compare this sweep with Post 126, Self Powered Mode (i.e. not powered by the USB BUS) gains about 5dB improvement in Phase Noise ? its still pretty grim?.

John

_________________
Hi-Fi??? "I may not be a psychiatrist but I know insanity when I see it - what ever happened to the normal old pervert who was content to sniff bicycle seats and collect women's shoes anyway?"

I think with the latest generations of the USB controllers they have worked out all the issues. I have used a friend's computer with a USB sound card while playing a game (Battlefield 2) that consumes 900 MB! of RAM and constant 100% load on CPU and graphics with no skipping or other issues.

Many of the previous generation controllers did not behave properly in some systems for whatever reason, specifically interruptions whenever a lot of disk or PCI IO occured.

As for software, I recommend Foobar2000 as a player. With DSPs disabled it has a bit perfect output on any device that supports either ASIO or Kernel Streaming. I have been able to play AC-3 encoded WAV files through it with a few different sound cards and have a receiver decode the output successfully.

Hi John,

Thanks again and let me try to comment...

Firstly, I see two good news... The carrier frequency is quite constant between the two measurements. And there is no bimodal distribution.

As for the phase noise level test results, I think they relate pretty well to the J signal analysis I?ve posted earlier. Jitter is mostly not data related, or the level of the data related jitter is pretty low, clearly lower than with the S/PDIF. OTOH, as the graphs you?ve posted to the other thread show, S/PDIF?s jitter is practically entirely signal related but has pretty low overall noise floor (this also relates pretty well to what I?ve posted about the differences between two interfaces).

Then, USB?s non data related discrete jitter components shift in frequency, dominant component changed from the one to another your graph from 294Hz to 222Hz and others components shift as well. In these two cases the different supplies were used but I wouldn?t associate this shift to this change... Another measurement of the same set up may reveal the facts. My graph actually suggested that the dominant frequency could be expected (to shift) between 3-4kHz but it is out of the shown range in the graphs you?ve posted...

The USB?s noise around the carrier (skirt) apparently has to be lower... Self powering obviously helps.

For me the hype about USB is not only the hype though the claims like it is free of jitter are apparently a bit excessive. These results point out something about the way the USB had to be further developed (and will hopefully contribute to the progress in this regard). However, yet at this stage I?ll be free to say that I can find this jitter structure more preferable than that of the S/PDIF...

Can you make/send time domain jitter measurement so we can have this figure quantified?

Pedja

I set those guys straight. I hope no one will kvetch that I posted on another forum...............

http://www.audiocircle.com/circles/view ... 928#228928

Happy now?

Jocko

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You are getting me going. It seems that the strongest proponents of computer audio supremacy are IT people; some of whom seem to know a lot about software (theoretically and dogmatically), and others who will believe in anything they say.

The sad fact is this. Computer Science courses can be one step removed from the real world. We were once invited to accredit a Computer Science course where students seem to spend four years in front of terminals 'engineering' software products, except that there was little engineering in it! What also horrified us was that there were not the requirement for students to have advanced maths as this was thought to be unncessary.

All this was in a university with a good reputation and well resourced.

We refused to accredit the degree as an engineering degree. Science maybe.

IME you can already have a taste of that with HDCD.

_________________
Carlos Filipe

"Any intelligent fool can make things bigger, more complex, and more violent. It takes a touch of genius - and a lot of courage - to move in the opposite direction." Albert Einstein

I see I struck a nerve. The "bits is bits" crowd shows their ignorance.

Again. As usual.

Must be an IT weenie. Right?

Jocko

Why bother, Jocko?
I have a PC at home since 1986.
I've first heard a CDP in 1983.
Software is my work since the end of the 80's.

But audio, music and electronics (applied to audio - since a kid, for family reasons) are my passion, my obcession since I know myself.
I've been following the development of the CD even before it was released, and after. With great interest.
Very soon I realized (even before buying my first CDP back in 1989) that a bit is a bit, there's Cross-Interleaved Reed-Solomon error correction as a standard on the CD-DA format, which guarantees a reconstruction of the missing data when there are read errors, but anyway, besides all this, there's still jitter.
So why bother with those who dont even know what they are talking about?

If those guys knew the CD-DA format more in depth and thought about what it signified back in 1982, they would soon understand that besides all the issues and the limited sampling frequency/bit rate, it was a HUGE achievement.
Many years later they even incorporated CD-TEXT, the extra bits were there, waiting to be used.
CD-ROM came later.
Audio was (and is) first.

_________________
Carlos Filipe

"Any intelligent fool can make things bigger, more complex, and more violent. It takes a touch of genius - and a lot of courage - to move in the opposite direction." Albert Einstein

.

In addition to the answers given by 00940, I would like to add: I do a lot of my music listening while I'm at work, so I've ripped all my CDs to my Mac using Apple Lossless. I used to carry two 64 CD cases with me between hom and work - but it was a huge pain in the butt to transfer the CDs in and out of the cases. I like having a huge variety of music with me. I want to be able to switch between listening to Static-X's Wisconsin Death Trip, then move on to Radiohead's Pablo Honey, and maybe follow up with some Beethoven - and I don't know what I'm going to want to listen to before hand. Carrying those CDs with me was just putting them in jeopardy in terms of loss and damage. By ripping them to my computer, they can stay in the relative safety of my apartment and simply go between my CD player and their jewel cases. Second, I do enough work on the road that I like to be able to take a good source with me. My iPod is functional enough for listening while taking public transit, but not when I'm camped out at a different University for several days working in a new lab. This way I can take it with me with my notebook and be reasonably happy.




I've never had any difficulty with any USB soundcard I've used with any of my three Macs or my PC, so I'm not particularily concerned.

I don't have enough money that I can afford to buy a high end CDP for home let alone my office, and I don't have the desire to transport CDs with me everywhere, so I think that this system will work very well for me.. And as 00940 said, we're doing this DIY - so it's also supposed to be fun.

*kvetch kvetch*

:)

Jocko,

vow... Shouldn't we run for a shelter now, with tail between legs..?

Pedja,

I couldn't agree more with Your analysis, in general. On the other hand, I would like to point out, in the defense of SPDIF, that John was showing the worst case situation in his measurements. With the Jtest practically there is no signal output, only sidebands present. With real life signals, at much higher level, what you get is rather a modulated noise floor, [like that present in the other thread, post 8], not so much those very obvious sidebands.

What I fear is that the difference between spdif / usb shown here is rooted in the fact that the designers, in case of the USB, were put in an even tighter corner than with SPDIF [now is that possible!!?] A PLL should be used. But the 1mSec packets should be captured. So no low & slow filter characteristics. So SPACT is really a miracle, but maybe not enough?

Because if You consider how clean those 16MHz XO spectra are when referenced to EITHER of these usb /spdif clocks, and consider also the fact that those XO are not the End, but only the beginning in the highend clock world..? I have the slight suspicion that there is at least two order of magnitude down the way of decreasing jitter from those ~clean MCLK spectra?

So probably USB should be totally reformed and switch to an another data protocol from the isosynchronous adaptive mode, before becoming a real candidate for high end.

Ciao, George

Clutz,

In spite of these explained above, I agree also with You. It's just a thing of the past, feeding CDs into the slot.. So it would be good to find a real solution.
But also John is right when saying that this present technology is just not serious enough. Though can be pleasant enough.

Ciao, George

------------------------------------------------------------------------------------I can assure you, no where near. Not much HDCD stuff around anyway

Because many of you insist on sending me mail, telling me what a bunch of twits they are. Expecting me to "go postal" on them for your amusement.

Careful, George..........you will be asscused of being scared.

"The horror.............the horror................"

OH......in case anyone from the "bits is bits" camp wanders back over here (we'll let them.........), care to 'splain why I am working on one of these. I must be trembling in my boots by now.

Jocko