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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

Showing 9 responses by seandtaylor99

seandtaylor99
1,262 posts
 
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
seandtaylor99
1,262 posts
 
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
1,262 posts
 
Thanks Steve.
seandtaylor99
1,262 posts
 
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.
seandtaylor99
1,262 posts
 
"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.
seandtaylor99
1,262 posts
 
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.
seandtaylor99
1,262 posts
 
"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".
seandtaylor99
1,262 posts
 
I think it's important to distinguish the different types of "computer audio".

The DAC might be on the sound card. I see this being a bad idea for reasons of noise.

It might stream SPDIF : this is also a bad idea for reasons of noise.

It might be streaming via USB. I can't see a problem with this so long as the DAC has a RAM buffer of sufficient size and a well designed oscillator and power supply.

It might be streaming via ethernet .... ditto USB.

Saying "computers can't stream digital" is an over-simplification.
seandtaylor99
1,262 posts
 
"The main difference of the Flash memory would be avoiding a spinning mechanical device and the problems inherent to these..."

I bet FLASH players and hard-drive players (and some CD-ROM based players, like meridian) actually play back via RAM, since they need to buffer and format data prior to transmission.

All can work well, but FLASH is currently disproportionately expensive.
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