Today's Transport War: Significant Differences?


I have been reading much these days about computer/hard-drive based transports as being a whole order of magnitude superior to traditional CD transports. In my reading, the camp who believes hard-drive based transports can render major improvements has been most notably represented by Empirical Audio. The camp which suggests that traditional CD transport techonology (or atleast the best of its sort--VRDS-NEO) is still superior has been most notably represented by APL Hi-Fi.

Each of the camps mentioned above are genuine experts who have probably forgotten more about digital than many of us will ever understand. But my reading of each of their websites and comments they have made on various discussion threads (Audiogon, Audio Circle, and their own websites) suggests that they GENUINELY disagree about whether hard-drive based transportation of a digital signal really represents a categorical improvement in digital transport technology. And I am certain others on this site know a lot about this too.

I am NOT trying to set up a forum for a negative argument or an artificial either/or poll here. I want to understand the significant differences in the positions and better understand some of the technical reasons why there is such a significant difference of opinion on this. I am sincerely wondering what the crux of this difference is...the heart of the matter if you will.

I know experts in many fields and disciplines disagree with one another, and, I am not looking for resolution (well not philosophical resolution anyway) of these issues. I just want to better understand the arguments of whether hard-drive based digital transportation is a significant technical improvement over traditional CD transportation.

Respectfully,
pardales
Hi,

Price level affects the answer to this question. You'll see quite a few comments where people say that their hard-drive-based transport "nearly equals" or "equals" their $3000-$5000 conventional transport. I take this to mean that the best conventional transports are still as good or better than hard disk based audio.

For those of us that are in the more common $500-$2000 CD player range (Rega, Arcam, etc.) the balance seems to tip towards hard disk based audio. Sound quality of the hard disk solutions is at least as good, and the convenience is killer.

There are currently relatively few hard disk based options (compared to conventional CD players). I think we will continue to see many more of these units coming out, and units from Sony and other mass-market manufacturers before too long.

- Eric
Very good point Ehart -- clearly a conversation about this topic in the cost-no-object realm would be different than in the budget and mid-price levels.

A few of the organizing issues seem, to me, to be:

1. The "rip" or how data is read

2. The quality of bits: are all bits equal?

3. And the whole USB/SPDIF/I2S thing.

There are probably other organizing characteristics that are important, this just reflects where I am in my understanding.
Isn't how the player sounds all that matters? If so, I would propose that there can never be a consensus agreement by experts or by laymen.

The Nova Physics Group Memory Player just received two big thumbs up on StereoTimes.com as the best digital the reviewers have ever heard. At $9995 retail, it's starting to look like a bargain reference digital player compared to the reference silver disc players on the market.
For me the sonic differences have been largely insignificant compared to the difference in convenience of having an entire library of music at my fingertips to mix and match as I choose. I find I do more listening this way rather than having to get up and change the disc every time I want a change. Call me lazy, but I'd rather listen futz around with my software and hardware.

I'm not sure if what you (this thread) are referring to is the one-box HD solutions, as Tvad mentions, and or PC-based audio as I'm using.

Let me go a bit more into how I view the differences as it may be revealing to those who choose to be more discriminating about these details. I've found that when you get beyond a certain threshold of investment, that the gains you get for dollars invested become very rapidly diminishing. Yes, I can hear the differences between my friend's $7K DAC and my outdated NOS DAC which can be purchased for $500-600 on the used market. But those differences are pretty small, IMO, compared to the HUGE difference in price. If you have the money, and want to invest it that way, have at it. I'd personally rather invest in more music. If I had invested additional money in small gains in hardware I think I'd end up feeling it was a poor investment for the gains got, but then everyone has their own threshold, and their own standards. The few times I've done side-by-side comparisons going into the same DAC, the differences between transport and PC/HD audio were not significant to me, nor were they consistent enough to pick out one specific, consistent fault going one way or the other. I would not put my system up there in the realms of great high-end reference systems, rather a modest entusiast's system, judged by pretty discriminating ears. Take it for what it's cost you to read this and the fact that you likely don't know me from Adam.

Marco
My reading of the POV of both Empirical and APL is that their preferences are independent of price, or nearly so. Empirical believe that hard-disk systems give us an opportunity to achieve better sound (by reducing jitter to practically nothing) than we can ever get from a transport spinning a disk. APL are vague on the specifics but seem to feel that the "environment" of a computer is far too polluting to yield seriously good sound. Steve says there's only jitter, nothing else to be concerned with. Alex had not yet weighed in on that. I respect and admire them both and hope I have not misstated their positions. Great stuff!
Steve Nugent of Empirical also says the best to be had is I2S. The Northstar transport with its' I2S output tweaked into a DAC with I2S input is the way to go, according to Steve. He says I2S properly implemented is "magic".
I've yet to see either camp come up with any meaningful data that would justify my $'s (i.e., if you can't measure it on the back side of a d/a converter then I doubt if you can hear it). Something I think audiophiles overlook is that digital data transmission is very forgiving by nature, as long as the bits get there at about the right time and at about the right magnitude, well designed equipment on the recieving end can reconstruct and reclock the 1's and 0's. You could watch a satelite hdtv and note the crystal clarity from the much higher speed digital data transfered back and forth through the atmosphere, and then decide if you want to worry about the bits from your transport crawling slowly to your dac across a couple feet of cable.
I'll be trying the North Star 12S interface shortly. I have had the transport for a while, and now just bought the DAC. It will be interesting to see how it compares with my existing set-up.
Jeff, in theory you're correct, but in practise I believe you're wrong, and the principal reason is due to the poor design of the whole transport - interface - DAC setup.

I agree with you that the 1s and 0s get to the DAC with no problem, but the issue is the DAC clock.

For high quality audio the DAC master clock should have very low jitter. Unfortunately the traditional method, where the CD transport has the master clock, and then the DAC has to try to reassemble the clock from an SPDIF or AES EBU data stream is a very poor scheme, and is entirely responsible for the fiasco of multi kilobuck transports and digital cables.

If DAC had been designed with low jitter master clocks, and the transport was slaved to the DAC I think we could have been using $20 CD rom drives, and ZIP cord digital cables right from the start. Many companies have implemented proprietary mathods to allow their transports to be slaved to their DACs, but it has never really caught on.

It would appear to me that Dan Lavry's approach of using a RAM buffer and a low jitter oscillator in the DAC is the best engineering approach to solve the bad situation. With enough RAM it wouldn't matter whether data were to come in from a PC (via USB, or ethernet) or from a transport (via toslink, SPDIF, or AES EBU).

I've never heard his DACs, they also may be compromised in the implementation, I don't know, but I've found the whitepapers on his website extremely informative.

There are several papers about 1/3 way down this weblink.

http://www.lavryengineering.com/supportpage.html
The term "hard-drive" based source is a bit misleading. The hard drive is only a place to store the data. It might be stored in RAM in the future or 3-D magnetic memory. The term should be "computer-based" source.

You can read this paper comparing computer-driven to CD transport:
http://www.positive-feedback.com/Issue22/nugent.htm

In a nutshell, the computer has the capability to "feed" the audio device in any number of ways - streaming at high speed, native speed, bursting or network packets. Many of these data transfer techniques have intrinsic buffering in them, allowing the D/A converter to be fed with a fixed clock rather than a PLL. Doing this with a spinning CD is much more difficult. The Lavry concept is a good one. I'm not convinced that it is jitter-proof however. I have at least one customer that replaced his Audiophile USB with my Off-Ramp Turbo 2 and reported that the sound was more clear and focused driving the DA-10. This should not have been the case if jitter were completely rejected. However I do believe that Lavry's DAC is one of the better designs on the market for jitter rejection, even though I have not heard one yet.

The point is that there is at least the opportunity to generate a non-PLL clock to drive a D/A chip directly with Computer-driven audio. Not so with a transport. You might say: well what about a word-clock driven back to the transport? It turns out that the reality of this is much more difficult than the concept. Most modern D/A chips are not even clocked on the word clock, it is the bit-clock or the master clock. To drive a DVD player for instance, you would need a 27MHz clock from the DAC to the Transport. Then you must divide this down inthe DAC to synthesize the clocks needed for the D/A converter. Then, in order to make this work, the D/A must resolve the phase difference of the Transport signals and the local non-PLL clock. The phase of these signals will change with the digital cable length, delays in the transport circuitry and clock generation etc.. The total timing budget is about 75 nsec for 24/96 signals, assuming S/PDIF interface. The slop in the reading of the bits from the optical head will probably eat-up most of this budget. The only way to pull it off is probably to FIFO buffer the data coming into the DAC to allow it to slop around. I'm not saying it is impossible, just more difficult and involves tight coupling of the transport and DAC. Mixing and matching transports and DAC's would not be possible. The Meitner system got around all of this by using an I2S interface. This is much simpler, but still relies on a PLL.

Steve N.
The Noiseball (aka computer) converts audio data many times, uses questionable performance clocking, has switching mode power supply and uses poor interfaces (mostly USB and Wi-Fi packets or combination of both) to transmit audio data to an external DAC. It does not really matter if the USB signal is converted to S/PDIF, I2S or anything else, it still comes from that same USB port! Same applies for Wi-Fi connection where the middle of the audio track may be sent first and then the beginning of it and so on in random packets which are then decoded and reconstructed by a DSP (talk about error correction). There are some nice pro-audio computer cards available allowing much cleaner data transmission and slave mode to the DAC clock, but please realize that all you slave to the DAC is the clock of the computer card DSP, nothing else.

Even a cheap $149 universal player spins the CD, SACD or DVD-A at higher speed allowing for memory buffering using both FIFO and large SDRAM buffers which results in “jitter free” clocks and “bit perfect” data. It is not true that the DAC in a CD/DVD/SACD player has to be PLL-ed (and what’s up with the “evil PLL” thing? Latest PLL techniques are great achieving as low as 30pS jitter!). Good example that comes to mind would be the famous, faulty and long discontinued Philips SACD1000. This player has its main 16.9344MHz non-PLL audio master clock (low noise powered) next to its DACs, the perfect scenario. This non-PLL, low jitter master clock oscillator is also clocking the audio DSPs. Then, PLL is used to generate the 27MHz clock for the video circuit. The SACD1000 spins the CD at much higher speed and uses combination of FIFO and large SDRAM buffers. The “jitter free” and “bit perfect” PCM data/clock transmission in the SACD1000 is carried by our beloved I2S but without any data conversion or long cables and connectors resulting in about 5-6 inches cleanest possible signal path. WOW, isn’t this amazing! It looks like the perfect CD player, the perfect solution, right? Well, I am sure that many around here know for a fact that the stock SACD1000 performance is nothing to write home about, although it was a nice machine for its time. The moral of the story; not everything is as easy and simple as it looks.

IMO and IME, a carefully optimized (key word), vibration/error free “classic” digital front-end using memory buffering and latest error correction engines, with built-in dedicated, specially designed DSPs, shortest signal path, no data conversions to completely irrelevant to audio data transmission formats, ultra low jitter clocking and low noise power supplies simply can not be outperformed by computer based audio, at least not for now. Hopefully in the future the time will come when proper technology will be developed so one is able to load favorite music onto a computer based audio solutions and play it back while achieving the same audio quality as with the classic dedicated stand alone digital front-end is possible today. So let’s stay optimistic.

Regards,
Alex
Aplhifi: if I'm understanding you correctly, you're saying that a vibration/error free front end as you suggest reads different data from a disc than would a lousy CD-ROM drive in a computer? Has this been tested, e.g. is it possible to somehow capture the digital data from a such a transport and compare it to a standard rip from a CD-ROM drive on a computer? Now that would be an interesting experiment! :)

If they are indeed identical, what then is producing the difference in sound? You stated that jitter is not much of an issue anymore, what else could be a factor if we assume that the DAC is identical?

I'd really welcome a discussion on this, it's so hard for me to understand what the problem really is. It should be so simple I think, but demonstrably it isn't since I've too found significant changes between various CD transports connected to the same DAC using the same cable and playing the same disc. How is this possible?

Thanks!
Grant a friend of mine whose products were on display at RMAF was brought down the Nova Memory Player you mentioned above. He heard this player on his system setup at the show after hours. The Nova player was compared heads up to the 10k player they were using in their listening room..he said he wants to purchase the Nova..The copy he made on the Nova and then played back on the other player sounded much better than the original cd played back on either machine. Electro mechanical jitter error correction all of that the Nova guys claim is pretty much gone.Playback from the memory chip internal of the Nova player is even better yet. The Melos crew is back! I recently purchased an Altmann Dac from Germany. Sounds wonderful. Altmann claims with his circuit redo's that the transport makes little or no difference..my listening comparisons so far are making me listen and look harder at transports differences when played thru this little 12volt wonder.Tom
Seandtaylor99 - Thanks for the link, interesting read.
Almost all DAC manufacturers will tell you transport doesnt matter, EAD manfacturer told me the same, because of the digital-flywheel thingy, Transport is very impotant I would say even more than DAC...

I guess If you destroy the original signal (say in a bad computer or a crappy DVD player) and then reconstruct it on the DAC, the result is not the same as if the signal is kept complete (as much as possible) from transport to DAC.

Thanks for that post Alex, it clears up a lot of things for me.

I hope the Nova memory player is indeed much better than a 10k transport, if that is the case we can say good bye to vinil, I hope its not just the next SACD!!!
"I guess If you destroy the original signal (say in a bad computer or a crappy DVD player) and then reconstruct it on the DAC, the result is not the same as if the signal is kept complete (as much as possible) from transport to DAC. "

How are you destroying the signal ? The digital signal is nothing more than 1s, 0s and timing information. I'll bet that even the crappiest DVD player's digital output has 1s and 0s that EXACTLY match even the most expensive transport. The $20 DVD-ROM drive in my PC seems able to extract and install windows XP without a single bit error, and it can do this while reading the CD many times faster than an audio CD has to be read.

A computer is quite evidently capable of preserving the 1s and 0s, since it's able to install an operating system from a CD-ROM. The computer might have jitter and noise on the output, but it's not rocket science to buffer and reclock data, to completely remove the timing jitter from the computer.
Js I agree that the transport sound can be even more important than the Dac...well maybe until this Altmann piece. I need to try some other drives to know for sure. I'm always in search of something better but right now this dac with a JVC dvd player sounds better than my last two rigs. Always in progress/I hope..Tom
"A computer is quite evidently capable of preserving the 1s and 0s, since it's able to install an operating system from a CD-ROM. The computer might have jitter and noise on the output, but it's not rocket science to buffer and reclock data, to completely remove the timing jitter from the computer."

Exactly my point. It is easier to do this with a computer because the data can be fed in a number of different ways that lend themselves to buffering and reclocking. The data is not necessarily coming on-the-fly like it is from a CD spinning at the native rate. You cannot re-read a block of data on a CD or read-ahead at high-speed and store the data in blocks. You have to provide the data on the first pass and continuously without breaks in real-time. If a CD-player is doing buffering and high-speed transfers of blocks of data, then it is actually a computer-based CD system, not a classical CDP at all.

Steve N.
"Hopefully in the future the time will come when proper technology will be developed so one is able to load favorite music onto a computer based audio solutions and play it back while achieving the same audio quality as with the classic dedicated stand alone digital front-end is possible today"

I'm more than optimistic. I'm already there.

Steve N.
Steve N.: "If a CD-player is doing buffering and high-speed transfers of blocks of data, then it is actually a computer-based CD system, not a classical CDP at all."

I guess this might be what I really want to know. Is it evolution, or, maybe convergence of technologies?" What would really be a classical, digital transport?

If we look at this, it may help us see where this is going...
Pardales - A CD-Rom based CD player is actually just a computer-based system. Maybe we are arguing semantics. I believe what Alex is arguing is something entirely different though. I just cannot figure out what it is....

Steve N.
What is Jitter? is an interesting read and offers a good reason for why transports sound so different.

I have setup a computer transport with great success. Its easy to get started but more effort/learning is needed to get best performance. After comparing my setup with some exotic (& very expensive) front-ends (Wadia 9 series, Esoteric P03/D03 & MBL Ref trans/DAC), I don't have a need to upgrade. Sound is superior to Wadia (bad dealer setup most likely here) & Esoteric (detailed but lacks musicality). MBL was excellent and couldn't be faulted but I don't need it.

It seems that computers are far better at upsampling than hardware based algorithms within a transport and/or dac. Upsampling after all is a computing function and doing it correctly, needs lots of processing power.
Cics, what computer programs are available that would allow you to rip, upsample, and potentially word extend and dither redbook CDs ? It seems like an interesting direction to go in.
Seandtaylor99 - EAC does a great job of ripping. Foobar2000 and SRC do a great job of upsampling. I much prefer this to spinning CD's because of the lower jitter and superior sound quality.

Steve N.
Empirical Audio
Manufacturer
Thanks Steve.
I much prefer this to spinning CD's because of the lower jitter and superior sound quality.

Sure! :-)

Regards,
Alex
Seandtaylor99 - Steve has listed the main software components. Also ensure that for whatever sound output device you use, make sure you have the latest software drivers and use a dedicated computer with latest software (Windows XP SP 2). In foobar2000, use either kernal streaming or ASIO for playback.
The Altmann article seems to align with some of Alex's point of view, if I understand the two of them correctly.
Drubin, to me the Altmann article just says that you have to minimize the sample clock jitter at the DAC chip. It doesn't infer that this is better done via a one-box, multi-box, or computer design.
Correct. But his discussion of the role of power supplies in creating jitter goes to Alex's "noiseball" doctrine. Or maybe I just don't understand this stuff well enough.
Drubin - with a computer external converter, the power supply can be just as quiet, whether it is USB or Wi-Fi.

Steve N.
Empirical Audio
We are not talking about the "external converter” and associates Steve, we are talking about the transport or the Noiseball which can not hold a candle against another transport featuring quiet linear power supplies. It's a fact. What good is external battery power supply when your data comes form the Noiseball? And BTW, the so called “super clocks” actually add jitter. But it sounds better right? So here is another puzzle to solve. :-)

Otherwise any DVD player or computer would sound satisfactory. Unfortunately, they don't. As far as I know Olive has a computer based solution (single box with control and HDD inside) with linear PS so that would be my best bet for starters.

But then again, it really depends on the level of audio quality one is after and what is his/her reference. Other than that Noiseball audio is more convenient, I admit. But what is up with evolution and mankind getting lazy? It was CD against Vinyl before now is the Noiseball against CD. It's funny! And why everyone around here forgets the High-Rez digital formats to which a CD is inferior, regardless of how it was processed.

Regards,
Alex
Nova Physics Group Memory Player is the latest buzz and is attracting rave reviews. It's essentially a computer with a tube based dac ($15k). You also get it without dac ($10k). One reviewer comments on how it outperforms the highly regarded Zanden front-end ($40k+).

So, yes its an evolutionary thing with a sweet benefit of lowering costs.
Yes the Reconstrction Theory....
The computer serves only to provide readable 1s and 0s, and evidently, despite their "noiseball" characteristics PCs are perfectly capable of reading 1s and 0s from CD roms, and hard-drives and streaming them over ethernet or USB without a single bit error. That's how you're reading this web site.

An external DAC can have its own power supply, and isolating any noise from the USB or ethernet inputs is not rocket science. Finally RAM based FIFO buffering and reclocking will feed the DAC a bit-perfect signal with noise removed and ultra-low jitter.

I understand that Alex produces respected machines, but I see no coherent engineering based arguments that refute any of what Steve (or I, or others) have said.
Regardless of the way we choose to play our Redbook, it makes me wonder if those in control of the CD mastering process are truly as critical as we are in our listening. How perfect is the mastering process? For that matter, look around and see how many professional recording devices these days have a USB port - what do you suppose that's for? Connecting to a "Noiseball" I reckon. Tells me that somewhere in the recording process our beloved 1's and 0's are quite possibly passing through a Noiseball. If so, is it possible that some of that noise generated garbage is being passed on to us in the final product? Are we just trying in vain to fix garbage that was already there?

I'm using a Meridian 518 to send my 1 and 0's from my computer to my DAC. My SPDIF converter is a Waveterminal U24 - which happens to be a professional audio device with , you guessed it, a USB port. The Meridian is supposedly a unit that (according to the manual) has been used in the final mastering process by Chesky records and Sony Classical, to name a few. Considering the above, perhaps I am doing no worse with the end product than what is being done in the studios in the first place?
The computer serves only to provide readable 1s and 0s, and evidently, despite their "noiseball" characteristics PCs are perfectly capable of reading 1s and 0s from CD roms, and hard-drives and streaming them over ethernet or USB without a single bit error. That's how you're reading this web site.

If this is what you believe in and makes you happy, so be it.

An external DAC can have its own power supply, and isolating any noise from the USB or ethernet inputs is not rocket science. Finally RAM based FIFO buffering and reclocking will feed the DAC a bit-perfect signal with noise removed and ultra-low jitter.

Simpe, isn't it? If you don't care how the "perfect" data was processed and transmitted that's fine too.

I understand that Alex produces respected machines, but I see no coherent engineering based arguments that refute any of what Steve (or I, or others) have said.

Thank you for the nice words! I am sorry but I can not further elaborate.

Regards,
Alex
Alex - I dont know what you mean by "Noiseball", but I do know that once you remove the digital and analog conversions from a typical computer chassis, whether it is using USB or Wi-Fi, this provides the opportunity to generate an extremely low jitter data stream.

Likewise, if you speed-up the CD player and make it essentially a CD-ROM drive and buffer the data, you again have the opportunity to generate an extremely low jitter data stream.

As for the computer sounding unsatisfactory, you obviously have not heard a good computer source yet. This is like listening to a $60 Walmart CD player and then proclaiming that all CD players sound terrible......and BTW, the Olive will only challenge good CD players once it is modded.

I have superb native 24/96 tracks mastered from tape in .wav format. I would like to see you play these on a CD player.

Steve N.
Okay, as of now (and this is just my read on the debate) the crux of the argument between the two positions I started this thread out with seems to be about whether the computer can send out a decent signal. Alex is suggesting that there is so much noise involved in the computer that it is not going to send out as clean/clear a signal as a classical CD transport will send to its internal DAC.

So, for now, I guess this is the question: is the average computer really putting out an inferior signal to that of the transport section of a good CD transport?

One camp says "no, not right now", and the other suggests, "yes, it now can".
Based on your answers, Pardales, I think the question you meant to ask is, Can the average computer put out a signal equal to that of a dedicated CD player or transport?
"So, for now, I guess this is the question: is the average computer really putting out an inferior signal to that of the transport section of a good CD transport?"

I think the key here is to define "inferior", and specifically "inferior in a way that would degrade the design of a competently designed reclocking DAC".
I do believe that the future of digital is through some kind of computer, Mr. Sprey from Mapleshade told me he has a wooden reinforced box for the computer in which he makes some kind of mixing. We all know the quality of Mapleshade recordings (amazing) He also said that going through a computer is hellish for audio.
I do think right now a computer setup can beat most high end players, but not the top notch CD playback systems.
We listened to the Olive and, though very good, when we compared against an Accuphase player (DP-75 I think)the diference was pretty obvious being the accuphase better(both stock) the related system was Halcro electronics and top Dynaudio speakers.

All the Best
J. Sarduni, it's good to see you around! :-) How have you been?

I do think right now a computer setup can beat most high end players, but not the top notch CD playback systems.

This is exactly my point!

Regards,
Alex
This has been a very interesting discussion thusfar. I have personally compared a purpose built computer with a very high end transport( not the esoteric, Alex)and have found the computer to nearly the equal of the transport for 16/44.1 playback. More recently, I have heard the computer via the USB converter that Steve Nugent makes and must say that for 16/44.1 the computer is the equal of and often betters the high end transport.
Whilst I can appreciate the pride of ownership that must accompany possession of a player such as the APL NWO 2.5 (which I must say I have not had the priveledge to hear), so far just from pure listening alone the computer is showing tremendous potential to be the ultimate "transport" IMHO.
By design a computer will always output a superior digital signal. Bit-perfect data is read from harddisk to memory then upsampled with much better precision. This happens in a ‘noiseball’ but critically outside of any realtime clocking mechanism and no bits are mangled/lost (essence of computing). Hence no jitter occurs during data prep stage.

Last stage transfers buffered data perfectly to sound output device (connected via usb, ethernet or internal bus). This device adds a clock and generates spdif signal for dac. This task will create jitter and needs to be optimal (clean power not sourced from noiseball, very high quality clock if dac does no input buffering and/or reclocking, etc.). All transports have same challenge here.

The way I see it, traditional transports suffers more jitter. In realtime, CD spins, data is upsampled (but not as good as a computer) then fed to dac – this all happens under a strict clocking regime. As noted in Altmann’s website (What is Jitter?):

“A simple CD player has multiple motors or actuators and associated control loops, in order to perform disc reading:
There are f.e. the spindle motor that turns the CD, the sledge motor that performs axial tracking, and actuators for focus and radial tracking.
Each of these motors / actuators will add a portion of noise to the power supply of the player and this noise will affect accurate switch timing.
So, each of the motors /actuators adds jitter to the digital audio signal and each adds a different kind of jitter (different in frequency, amplitude, waveform) and will affect audio reproduction in different ways.”

Put another way, jitter is compounded by the spinning CD which induces various types of power supply jitter. (I can see why esoteric built the VRDS Neo mechanism.)

Nova’s Memory Player does away with spinning CDs in realtime. Playback is driven by a computer.
Much of the above technical discussion is interesting and yes, I do accept that data stored on a computer's hard drive can be superior.

There are, however limitations. The first has to do with the format used to rip a CD. Everything is most dependant on the DAC used. I just purchased a Slimdevise TRANSPORTER which has a really high-end DAC and now my music on my computer as well as streaming audio is as good as my stand-alone CDs. Getting to this point took a while.

I had never been happy with my Apple G5's ability to play back my music. I have an Audio Aero Capitole CD player and I have a pair of bridged McIntosh 2102 amps and my speakers are Kef Referance 205s. Music from my computer, even using Apple lossless or WAV simply never equaled what I got from my primary system. I ordered a TRANSPORTER, but since they were back-ordered they gave me a squeezebox for free and this was an improvement. Then, the Transporter arrived and it sounds great. It has several digital outputs, including a balanced AES/EBU which makes it the first unit i have owned that actually outputs this signal. It also outputs toslink, coax and SP-dif. I have tried all three as my Audio Aero will accept any of these and the SP-dif sounds the best. Even streaming audio sounds good.

So, yes pure data well stored is fine; don't ignore the system's retrieval ability as cold science is still cold.
I'm confused. You say the Transporter has a great DAC, but it sounds like you are taking its digital out and using the DAC in your Audio Aero.
Good question. The Transporter's DAC kicks in before it releases the Info. The feed from my transporter sounds much better than from the squeezebox using the same S/P DIF digital cable.
There will always be terms that need definition. I still think that where we are in this discussion is trying to answer the question of whether a computer can put out a digital signal equivalent to what a classical CD transport can put out.
Pardales, have you tried a top transport in your system?
How does it compare to the Hag-usb link?

As always a general conclusion will never be met, but a personal conclusion can be drawn....

I tried computer audio and a good CD transport makes a world of difference in my system, anyway I will some day buy a computer interface with SPDIF and try it out again, maybe the next generation will be better....but I will try again Analog first!!!

When a computer link sounds better than my Forsell in my setup I will be convinced!!!