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USB to SPDIF converters shoot-out : EMU 0404 USB vs. Musiland Monitor 01 USD vs. Teralink-x vs.... - Page 22  

post #316 of 1712
Quote:
Originally Posted by tosehee View Post
Are you saying that resampling in PC/Mac is generally bad or ?
The problem with resampling in a DAC is:

1) the resampling clock quality is usually poor
2) the resampling algorithm used in the chip is usually poor compared to a good static software upsampler

Quote:
So, am I correct in saying that SPDIF converters and such that supposed to fight the jitters from PC to DA is useless since most of the DA already does some form of reclocking and the jitter where it matters the most is usually inside the circuitry?
Not useless, just usually not very effective. Most of these chips do reduce jitter a little, the resamplers, the receivers and even the D/A converter chip itself.

The problem with resampling in hardware is that your are stuck with the jitter of the resampling clock and you are stuck with the quality of the resampling algorithm. Better to have a DAC without resampling IMO.

Steve N.
Empirical Audio
post #317 of 1712
Quote:
Originally Posted by audioengr View Post
Sorry, it was UHF magazine, not VHF.

I have misplaced the issue, so I asked the editor again. I'll let you know when I know. Hopefully, it's in these back issues:

The UHF Reading Room

Steve N.
Empirical Audio
Thanks, certainly interested in reading the results.
post #318 of 1712
Quote:
Originally Posted by gevorg View Post
Dan, does this mean that there is no such thing as "software jitter"? In other words, can different operating systems (Windows and Mac) or playback software (Winamp, Foobar, J.River, etc) have different effect on jitter? Assuming, in all cases that the digital output is set to bit-perfect (no digital volume, EQ, DSP, etc) and you're using the same device to output digital out.
Dan may not have enough experience with computer audio to answer this. It's a tough question.

There are jitter contributions due to the software running on the computer, as well as other effects. Trying to determine how much of this is jitter and how much is "other" is very difficult. The best one can do is probably to hear "relative" changes.

I performed an experiment with Amarra earlier this year to try to determine if the improvements I was hearing with Amarra were only jitter or something else. The experiment went like this:

1) first use Off-Ramp 3 USB to I2S converter and play selected tracks using both iTunes and Amarra
2) second use Pace-Car reclocker to I2S and play same selected tracks using both iTunes and Amarra

If the improvement of Amarra was primariily jitter, then iTunes and Amarra should sound identical with case #2.

This was not the case.

Also, the improvement with Amarra occurred with both Pace-Car and Off-Ramp. Conclusion is that both jitter and "other" are being improved with Amarra. This is because the Jitter is mostly eliminated with the Pace-Car.

Steve N.
Empirical Audio
post #319 of 1712
Well I have an issue which is leading me eventually to a converter it looks like. I have a rebuilt, reclocked usb section in my dac which seems to top the optical cable out of my mac(i am new to macs). I am getting a higher end usb cable(already ordered). My issue is that my main clock(Ultraclock) in the upsample is still a higher level than the clock in my usb section(Suoerclock) and i don't know if I am getting use out of it. In addition-and here is the kicker- I seem to have been importing more and more 24 bit files and my dacs usb section can't handle 24 bit, only the other inputs can.

So I hate to get a converter that still for 90% of the music won't be used or is lower end than the usb section that i have.....the clocking on my usb section alone was around $500. so I expect it would be hard to beat it on normal files.

I have been shuffling this back and forth in my mind for a bit, the 24 bit files are great and maybe I just have to settle for the optical out on the mac, has anyone else compared the optical to usb?(i ask without using the search-bad me). It seems muddier on normal files......i compared my wifes and mine a/b using same songs, switching back and forth-But doing this i have to take the Amarra out of line and do straight itunes.
post #320 of 1712
Quote:
Originally Posted by nick_charles View Post
Thanks, certainly interested in reading the results.
It's issue 74:

Contents, UHF 74

I guess you must pay for it.

Steve N.
post #321 of 1712
Quote:
Originally Posted by dallan View Post
Well I have an issue which is leading me eventually to a converter it looks like. I have a rebuilt, reclocked usb section in my dac which seems to top the optical cable out of my mac(i am new to macs). I am getting a higher end usb cable(already ordered). My issue is that my main clock(Ultraclock) in the upsample is still a higher level than the clock in my usb section(Suoerclock) and i don't know if I am getting use out of it. In addition-and here is the kicker- I seem to have been importing more and more 24 bit files and my dacs usb section can't handle 24 bit, only the other inputs can.

So I hate to get a converter that still for 90% of the music won't be used or is lower end than the usb section that i have.....the clocking on my usb section alone was around $500. so I expect it would be hard to beat it on normal files.

I have been shuffling this back and forth in my mind for a bit, the 24 bit files are great and maybe I just have to settle for the optical out on the mac, has anyone else compared the optical to usb?(i ask without using the search-bad me). It seems muddier on normal files......i compared my wifes and mine a/b using same songs, switching back and forth-But doing this i have to take the Amarra out of line and do straight itunes.
With these older USB interfaces, adding Superclock or even Ultraclock is like polishing a turd. Better off to get a more modern USB converter that supports 24/96 or even 24/192. These can come with Superclock or Ultraclock, and you get the advantage of volume OEM pricing on these. I am working on an async 192 interface, but it will not be available until late Q1 2010.

Steve N.
Empirical Audio
post #322 of 1712
Hmm, okay, I ordered this dac in June and had to wait two months for the Ultraclock on backorder....it is a current dac and after hearing many, i liked the way this one sounded, very open and dynamic. So it is-after modding, around 2 months old. But I do understand the usb problem, that is why I ask, kind hard to choke down though, shouldn't have upgraded the usb section, just should have bypassed it...that would have kept my cost at under $2000. instead of over $2000. and i would have been able to get the converter outside the dac. I had one breifly that I returned because I wasn't satisfied with it before i owned this dac.

Edit-So the answer is to get a newer converter with an ultra clock or super clock in it...or use the optical.
post #323 of 1712
Quote:
Originally Posted by slim.a View Post
It seems that m2tech has solved their shortage issue and that many people are getting their ordered hiface. It would be nice indeed to have more impressions on that unit.
Got this from tweekgeek today

Quote:
Hello everyone,

It looks like the HiFace will be leaving Italy on this coming Monday via Fedex. If I have them before Wednesday the 25th, They will ship the week of Thanksgiving. Otherwise they will ship the following Monday the 30th.
post #324 of 1712
Quote:
Originally Posted by audioengr View Post
Dan may not have enough experience with computer audio to answer this. It's a tough question.

There are jitter contributions due to the software running on the computer, as well as other effects. Trying to determine how much of this is jitter and how much is "other" is very difficult. The best one can do is probably to hear "relative" changes.

I performed an experiment with Amarra earlier this year to try to determine if the improvements I was hearing with Amarra were only jitter or something else. The experiment went like this:

1) first use Off-Ramp 3 USB to I2S converter and play selected tracks using both iTunes and Amarra
2) second use Pace-Car reclocker to I2S and play same selected tracks using both iTunes and Amarra

If the improvement of Amarra was primariily jitter, then iTunes and Amarra should sound identical with case #2.

This was not the case.

Also, the improvement with Amarra seemed to be larger with Off-Ramp 3 than with Pace-Car. Conclusion is that both jitter and "other" are being improved with Amarra.

Steve N.
Empirical Audio
Sorry, I stopped reading after you mentioned Amarra. And you did not show any proof or at least solid explanation that software jitter exists.
post #325 of 1712
Quote:
Originally Posted by dallan View Post
(i am new to macs).

Edit-So the answer is to get a newer converter...or use the optical.
Are you using your Mac as dedicated music server, or is it used for other purposes?

Yes, to the question above. Get a USB to S/PDIF converter that has a very good re-clocking circuit.

Peace,

Lee
post #326 of 1712
Hi Lee,
Yes you were right about the eventual problem with 24/96 files. And yes to your suggestion months ago, I did go to the macbook pro as basically a dedicated music server. Not thrilled with the optical output though. The one in the dac is okay with the Superclock in it but no 24/96 so is now starting to be a pain going back and forth. The Amarra is wonderful, I got a lot of good suggestions from you this year.
Dave
post #327 of 1712
Quote:
Originally Posted by regal View Post
Its pseudo-science because the DAC developers who come up with the jitter reducing schemes don't have any reliable way to measure the jitter. ASTM doesn't have a test method for jitter in digital audio, until it does it is just marketing and black art stuff. Not saying its meaningless just saying its definately not an empirical science, yet.

Think about it this way, measuring Jitter is of the same order of magnitude as measuring the speed of light. It takes highly calibrated equipment with standards to make this credible.

There are a lot of indirect methods of measuring jitter but they require a leap of faith that hasn't been accepted anywhere in the literature.

I sure hope that if that person ever needs an MRI test, that the converters inside the MRI gear operate with low enough jitter, or else the image pictures will be fuzzy and distorted. Jitter is not some audio thing. Jitter is an issue for ALL conversion, be it medical, weighing scales, digital video, industrial, telecom.... name it. Jitter is a timing error. Given that nothing is ever perfect, there is always some timing errors, and the question is at what point the error gets to impact what you are trying to do.

Jitter is a part of electronics. There is equipment to measure jitter, and it is costly. Look at Agilent (the original HP) and Tektronix sites. Some of that gear costs $100000 and people in the technology field are not just buying it for the hack of it.

Jitter is becoming a major issue for speeding up digital communications into the many GHz range. At say 10GHz, a clock cycle is 100psec (50psec up and 50psec down) so you can see that a timing error of 60 psec can “ruin your day” (you miss or repeat data!). Measuring jitter for audio still very costly. But a good Audio test gear is also costly. As a rule, good jitter test gear is over $10000. Same for good audio test gear. I would call it costly science, not pseudo science.


For audio, the jitter is important because the ear has an ability to hear tiny imperfections, and timing errors cause noise and distortions. The "basics" are not too difficult to understand:


Say you have a video camera and a video projector. The idea is to first “record” video frames with the camera, then to project them with the projector. But for the concept to work, both the camera and the projector should work in a very constant rate. Say your camera (the recording device) takes 50 picture frames each second. You want the time of each frame to be .02 second because .02 X 50 is one second. You also want the projector (the playback device) to project 50 frames each second at the same rate, one frame each .02 second. What would happen if projector speed is not steady? Say the first 25 frames are .01 second each, and the next 25 frames are .03 second. You still have 50 frames in one second but there are timing errors.


If your movie is about still object, then there is not much harm done. But say you are taking a movie of a ball moving from the left side of the screen to the right, I one second. If the first 25 frames are too fast, and the next 25 are slow, the ball will get to the middle of the screen in ¼ second, then it would slow way down and move through the rest of the screen is .75 second. That is a distortion due to timing errors, a jitter induced distortion.


Video is not audio, and analogies may be misleading. I am just doing my best to show how a timing error can cause distortions. In audio, the idea is to take samples with AD at as constant time intervals as possible (lowest jitter) and then play back with the DA with the lowest jitter possible. If there is jitter, your playback will “place” the samples at the WRONG time. The output voltage of the DA will be distorted.


You can see that jitter has impact at BOTH the AD and the DA. You need to take the samples at the record side with low jitter. Once the samples are taken, they are just “numbers” describing the sample amplitudes. Those “numbers” (values) can be stored in a memory, on a CD or what not. You can send the data down a cable, and timing is not much of an issue. You can even send music data in “chunks”, and timing jitter is not much an issue as long as you get receive the sample values as they were. But when you want to play back – the conversion of the numbers has to be with good timing to match what happened at the recording side. That means keeping the conversion jitter low.


How low? That is another matter. I already posted numbers showing the impact in bits. How low can one hear? I will let you argue that, and I did point out that the music itself has to do with it. As in the video example, a slow moving object (or a low frequency content) is less impacted by jitter. A fast moving object (or a fast signal at high amplitude) are very impacted by timing errors (jitter).

I hope my post provides basic enough information to understand that jitter is not just one more made up stuff such as the "need to keep a minimum cable length".

And while direct measurements of jitter are costly and require much expertise, the IMPACT of jitter in terms of distortions and noise is measurable with a good audio test system. The key is to decide what kind of distortion, and at what level the ear is impacted. Clearly, if I suddenly stopped you CD player for an hour and then restarted it, you would notice such huge timing error. That is very extreme. Can you hear a 1psec slow down? 100psec?

The science is there, and it is very solid and real. For audio the question is the impact of jitter on the ear. For instrumentation and medical the question may be “how accurate is the result”. For video, it may be about fuzzy picture, distortions coloration…

One can look at some "pictures" and explanations in my 1997 paper "On Jitter":

http://www.lavryengineering.com/white_papers/jitter.pdf

I may be deviating from the subject of the thread again. I will take some time to answer off topic question and comments addressed to on the Lavry Forum here at head-fi.

Regards
Dan Lavry
Lavry Engineering
post #328 of 1712
Quote:
Originally Posted by audioengr View Post
It's issue 74:

Contents, UHF 74

I guess you must pay for it.

Steve N.
Print copy ordered, tried their online service but it was total pants !....look forward to reading their results
post #329 of 1712
Quote:
Originally Posted by dallan View Post
Hi Lee,
Yes you were right about the eventual problem with 24/96 files. And yes to your suggestion months ago, I did go to the macbook pro as basically a dedicated music server. Not thrilled with the optical output though. The one in the dac is okay with the Superclock in it but no 24/96 so is now starting to be a pain going back and forth. The Amarra is wonderful, I got a lot of good suggestions from you this year.
Dave
My pleasure. E-mail me for a couple quick suggestions of how to optimize a couple aspects of the Mac that is dedicated to music playback.

24/96 files are addictive, be careful.

Peace,

Lee
post #330 of 1712
I know i am listening to one now.

Actually though I think these are 24/48
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