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In Reply to: RE: A very technical curiosity - how to assess the quality of a spdif stream ? posted by beppe61 on May 18, 2015 at 04:12:04
I could have swore some people here had programs that measure jitter?
I could remember seeing graphs and what not. Is that what you are talking about?
Follow Ups:
Hi not that in particular. Mine is a very general question.
Just that i remember the old discussion about different transports.
I remember that most of the opinions were based in listening tests.
I would expect a more scientific, reliable and less time consuming and frustrating method to assess a transport/digital source quality.
For instance how a transport manufacturer can be sure that its product has a great spdfi out ? by listening it ?
i can believe this.
There must be an instrumental way to assess this.
And i have always had another feeling. That a good transport must not be that expensive ... maybe i am wrong about this.
Kind regards,
bg
Edits: 05/18/15
1. Loop the output back or send it to another sound card. Run for a long time and make sure that all the bits received are the ones sent. This can be done by recording the SPDIF output and comparing the source and destination files.
2. Use a scope and look at the eye-pattern. This will show the presence of noise and reflections on the signal as well as gross jitter. This will also show the signal levels.
3. Measure the clock rate with a frequency counter.
If the signal passes these tests then it's good. Whether the resulting sound is good or not will depend on the DAC that's connected to the SPDIF source.
Tony Lauck
"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar
"Use a scope and look at the eye-pattern. This will show the presence of noise and reflections on the signal as well as gross jitter. This will also show the signal levels."
Tony, I can see how to put the SPDIF bit stream on one scope axis, but how do you connect data rate to the other one? Can you refer me to a "how to" paper or similar source on the web? BTW, I have a pretty basic 30 Meg two channel single beam analog scope, and I would like to play around with the eye-pattern measurement. I looked at the HP article that you referenced, and their method seems to involve a lot of ancillary instrumentation. Thanks in advance.
You can trigger the scope on the data or various other ways, depending on your equipment.
Tony Lauck
"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar
Hi and thanks a lot for the very valuable explanation.
So it can be done and with reliable results.
It was mostly a curiosity because i read many reviews about transport-dac matching.
However i have also to say that when a transport unit is good it is good with many dacs.
So to me lab testing of different transport solutions could be very interesting.
Then of course just a very good spdif signal is not enough.
Let's say that it would be a good start ?
Because i also remember matching of exceptional transports with just decent dac with a resulting sound that was quite something.
Thanks a lot again.
Kind regards,
bg
Yes, if a transport is good it will be good with many DACs. By the same token, if a DAC is good it will be good with many transports. However, it's best to evaluate the entire playback chain as a system. That's what needs to be good. :-)
Tony Lauck
"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar
Hi and thanks a lot and i agree completely of course.
But what makes me really nervous is how digital signal are transmitted from a unit (transport for instance) to another (dac).
I am a complete ignorant but the fact that reliable and effective standards for this duty are available and still not used makes me very angry.
For instance. Why do not use the AES/EBU that from what i understand is a decent standard everywhere ?
A transport usually is a mid to high price unit.
It is not a cheap product.
It is asked to send out a good quality digital signal.
it should deserve a AES/EBU or at leas a bnc connection.
This would make the transfer better in terms of quality.
And the same for the receiving dac.
I would like to see this AES in dac from 4-500 USD up.
Only one very good standard.
Instead i read of RCA not being impedance matched (?), toslink with jitter issue ... this is pure perversion.
In absence of good alternative i could understand but the solution is already here just to be caught.
Better S/N ratio, noise rejection ... i am inventing things here.
Then i also discovered that a trivial ethernet cable is much better for video signals than an expensive HDMI and i understand Shakspeare ... All the world's a stage ...
Thanks again.P.S. just to say ... same video card same display ... the hdmi out compared to DVI is pure shit ... just to say
Then i see video processors of tenth of thousand of dollars with hdmi, clearly to me a bad standard from various point of view.
It is clear that there is something really bad going on
It is the worst who wins
Kind regards,
bg
Edits: 05/20/15 05/20/15 05/20/15 05/20/15 05/20/15
I think it would be more accurate to say that expensive transports don't necessarily sound good. But if you want to design a good one you'll have to pay attention to vibrations, power supplies, jitter, etc, and the quality of the components involved will necessarily have a cost.
Now at some point like with all things hifi there's also going to be a law of diminishing returns.
Edits: 05/18/15
Hi and thanks for your reply.
When you say " if you want to design a good one you'll have to pay attention to vibrations, power supplies, jitter, etc, and the quality of the components involved will necessarily have a cost " you exclude the possibility of cheap and good.
I do not know for sure.
Kind regards,
bg
I guess it's like a car. You can get a cheap and good car like my Fiat 500. I love it.
A Porsche is much more expensive and will outperform it in every respect. I don't feel that I need a Porsche, I'm happy with my Fiat 500, so it all depends on what you want in life.
Thing is, with audio, differences are less pronounced than between a Fiat 500 and a Porsche, that's for sure. But now that I own an Esoteric (and older one), I wouldn't settle for less. It's a fantastic transport.
Hi and sorry to have been not clear
I am sure that great and expensive transports like your Esoteric are really great because, as you say, all the issues have been carefully studied and faced in the design, careful parts selection and so on.
But i am not completely sure that, for instace, a cheap but very good way to play a cd does not exist.
I am not an expert but as someone i think did, to use a cheap cd rom to fill a 1 GB buffer and then read with good clock from that buffer should not be that difficult and expensive.
And that stream could be very high quality spdif signal for an external dac. There can be different ways to achieve a similar result i mean.
I would be willing to wait for that buffer to be filled.
I am waiting for a br player said to be a very nice transport.
I am curious to hear ... very.
Kind regards,
bg
Hi,
> I am not an expert but as someone i think did, to use a cheap
> cd rom to fill a 1 GB buffer and then read with good clock from
> that buffer should not be that difficult and expensive.
Early PC based "Memory Players" did precisely that and got good reviews. I never experienced those, because at that time I was already on file based for digital.
Before that, the only platform that used read CD "asynchronously" were very early (first gen) DVD Players that lacked a separate laser and chipset for CD-Replay. It meant they were no-go for CDR, but some CDRW+ blanks recorded did work.
I owned one, from pioneer, which incidentally featured the same HD "Legato Link" DAC chip as the Stable Platter Pioneer CD-Player used by Tom Evans for the legendary EIKOS modification.
I had a lot of fun modding this unit, it was extremely responsive to tweaks and once I was done made both an exceptional Player via analogue out (using LC Audio Zero Feedback "Zap-DFilter" anlogue after the DAC - fully balanced) and via digital out (a reclocker plus 16.XXXMHz clock that also fed the CD Playback with separate PSU etc) into DAC's.
I had it beat the Eikos via both analogue and digital outs and among others a Teak VDRS Transport as well as Pioneer Stable Platter, CEC Belt Drive etc. The Mechanism was an early plastic DVD one, plastic drawer, cheap and nasty as they go.
The key was that the CD was read as "Data Rom" and stored in RAM before leaving the DVD Chipset. On errors it would re-read (it was fun to watch this one with damaged CD's with the Top Off). It was possible to stop the disk for a moment and playback would continue, if the disk was released sufficiently quickly to restart reading before the buffer ran dry, playback would be uninterrupted.
Later DVD players put in effect a full CD Player back in, cancelling all the good stuff.
I sold the unit many years ago in a cleanout, a year or two it came for sale and was still going like a trooper (unlike many early SACD Players). So I think that there is some merit to your ideas. No need for 1GB, IIRC DVD had 16MB RAM...
Ciao T
At 20 bits, you are on the verge of dynamic range covering fly-farts-at-20-feet to untolerable pain. Really, what more could we need?
Hi and thanks a lot for the very informative and valuable story.
Actually it is what is done now with the computers. Files from cds are ripped, stored and played-back from a solid memory.
One of the main reason to abandon cd players is the reliability of the mechanisms and the very different performance between cd players/transports.
Honestly i liked very much the huge cd transports ... just beautiful.
But really needed ?
Anyway a really complex field this one. No easy solutions at all.
Thanks again.
Kind regards,
bg
What makes the VRDS-NEO SOTA, and possibly the best transport, has nearly nothing to do with any software/firmware whatever.
A big, powerful, overbuilt, accurate motor, a magnesium clamping mechanism the size of the disc, an incredibly quiet, power supply, first rate connectors, wiring....
You cannot mitigate hardware corner-cutting with better software design. The VRDS-NEO proves that error correction has clear limitations.
The essence of great sound is HARDWARE.
"Asylums with doors open wide,
Where people had paid to see inside,
For entertainment they watch his body twist
Behind his eyes he says, 'I still exist.'"
Hi and yes i understand the exceptional design and build of the Esoteric.
I still wonder if different approaches can also be very good at a cheaper price, just that.
Like for instance, as i asked above, a cheap decent cd rom reading the tracks and storing them in a buffer memory from which the bits are read and played-back with high precision.
Morevover a mechanism can always develop mechanical problem.
To replace a cd/dvd rom is almost no cost.
Less than the price of a cd let's say.
Thanks again.
Kind regards,
bg
I understood your point. I've been looking for cheap solutions for a long time too.
The problem is digital is an extremely complex world, more so than analogue, with crazy little elements having a major influence on sound. Just burn one of your commercial CDs on a high-quality CD-R like a Taiyo Yuden and you will discover the CD-R will very likely sound much better. And that's just from the same CD, same 0 and 1s.Now imagine that every part will have an influence on sound, and that's where the problem begins. Part selection, design work, etc... are bound to end up being expensive. That's why a lot of manufacturers using CD-Rom drives produce expensive machines, because they just can't stuff one in a box. Too many elements influence sound.
The best solution to get something cheap, I've discovered, is to buy a well-designed machine which is from an older generation. You get great design at a fraction of the price. And I don't really believe, despite marketing hype, that digital has advanced that much. I believe you can achieve state-of-the art sound with a 10 year-old machine. My UX-3 is 10 years old, so was my previous YBA CD1. They weren't cheap but they weren't crazily expensive either.
JB
Edits: 05/19/15
Hi and thanks a lot for the valuable advice.
I have abandoned the optical medium that i still have of course in my musical archive
But this is off section ... let's say that i get up from the sofa much less nowadays when i listen to music... and it could not be a good thing.
I have become more lazy.
Thanks a lot again.
Kind regards,
bg
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