How important is the source? - Page 4

This si exactly the question I came to in the other thread. When the drive reads the CD to write it to the hard drive as a lossless file, is that the equivalent of when the drive in a CD player reads the CD to send the data to a DAC, meaning that it has the same opportunity for jitter or minor read errors that would then be permanently preserved in the song on the hard drive?

-Jay

No, this is completely different. When a CD is read and the data is sent to the DAC, it's sent via the SPDIF protocol, which lacks clocking and error correction. Various interference can cause certain data bits to get lost. Given that there is no error correction, those bits do not get resent. Hence, jitter.

When you copy CD files to the Hard drive, that transfer is handled like any other internal computer data transfer. The internal data transfer mechanism does not use SPDIF, therefore there is clocking and error correction mechanism utilized. Hence, no jitter.

Right, I understand that the S/PDIF protocol is very jitter prone and has no error correction abilities, but I was under the impression that that was only one source of possible jitter and that minor errors in reading the CD by the laser was another cource of possible jitter. Is this true? And also, when you are using a standalone CD player as the transport and the DAC (no outboard DAC), does the transport part of the player use the S/PDIF protocol to send the data to its internal DAC? I guess more specifically, is it possible to have jitter between the transport of a CD player and the CD player's own DAC?

-Jay

The actual laser mechanism that reads data off the CD has error correction. So, if a CD is read by the transport and it encounters an error, it reads it again. There is a small buffer that allows minor errors to be corrected without interrupting the stream.

AFAIK, the communication between the CD transport section and the built-in DAC within a CD player uses s/pdif protocol. However, the possibility of jitter is diminished because of the short pathways between the two. Not to say that there is no jitter at all, just that due to the short distances envolved the chances of interference, in a properly designed and isolated CD player are diminished.

A very good link with lots of info on jitter:
http://www.digido.com/portal/pmodule...er_page_id=28/

Well if I understand that article correctly, it says that jitter is irrelevant in a playback system until when it is converted to analog. This to me means that you can't really have jitter when playing a CD that can't be fixed at the end of the chain (even if coming from a hard drive source). But it also says that jitter is cumulative, so the more steps you have in your chain that are succeptible to jitter, the more the DAC will have to fix at the end. Perhaps this is why some computer transports don't sound as good as a quality CD transport even with a DAC that reclocks. There is just more to fix and the DAC jitter eliminator might not be 100% effective. What a complicated and confusing topic.

-Jay

I've just been thinking about different methods of using a computer as a source and I have come to the conclusion that the Airport Express is probably about the very best or just about the very worst computer transport. If it uses an error checker after being transmitted wirelessly, it probably does phenomenally well. Once the data arrives at the AX unit and is checked and corrected for errors, the bit perfect output would then be away from the possible interference and contamination that is common in and near the computer box. It can then go directly from the AX to the DAC, meaning that the only place for jitter to appear is inside the cable. On the other hand, however, if the wireless transmission to the AX is done with something similar to the S/PDIF protocol with no error checking, I would think that the amount of possible jitter during the transmission through the air would be huge, and then it would just get worse once in the digital cable from the AX to the DAC. I'm sincerely hoping for the first option, because I love my AX and I would love to think it's a great transport.

-Jay

That was an interesting article.

You should research SA-CD and DVD-Audio. When you're done, go research DVD+, DualDisc, and SA-CS2CD!

I know the "source-first" debate has been going on for a long time; and I am a relative newcomer. But allow me to interject, or at least clarify a few things that may help focus the argument a little better...

First, there is a difference between a philosophically important link and a practically important link. I.e. Philosophically speaking - the source is of primary importance because it is the start of the chain. It has the possibility to weaken signal before anything else. However, philosophically speaking, it is not more important. This is because any link has the possibility to weaken the signal to the point of either eliminating the signal entirely or replacing the signal entirely (with noise or some other signal). Therefore, merely stating that the source is the most important link merely because it is the first is overly simplistic.

However, I am not trying to argue that the source is not important! Hear me out! I am merely trying to prevent "philosophical" arguments in a "practical" argument.

So then. what makes a link more or less "important" in a chain? I'll explain, on a scale from 0-100 (Zero being "cannot pass a signal/completly replaces the signal" and 100 being "transmits a signal perfectly in every way") imagine that every piece of audio equipment could be assigned a place (I know this is overly simplistic, since there are subjective qualities to take in account, but just bear with for a moment). A more important component, i.e. one you should spend more money on, would have a greater variance in range between the highest and lowest points on the scale. For instance, a $10 cable may score a 75 while a $1000 cable may score an 85. However, a $10 pair of headphones may only score a 50 while a $1000 pair of headphones may score a 90. Therefore, practically speaking, the headphones are more important than the cables, merely because it is "easier" to get good sound from a pair of cables.

However, things are more complicated than that because of subjective matters. Therefore it is necessary to also add "subjective weight and quality" to the equation. That is, "how much does this item affect the sound?" and "how pleasant/unpleasant is the effect?". This is much harder to quantify. For instance, IME cables have very little subjective weight. While there is a certainly some variance among the accuracy of transmission, there is little change in the sonic character apart from the changes due to accuracy. With headphones, on the other hand, two headphones may be very close in accuracy to each other, but they both sound VERY different. This is because headphones have a very high subjective weight, IMO.

This may seem like common sense; but I have seen alot of philosophical argument in this practical argument (and I don't intend the term "argument" to connotate hostility!).

I hope this will help clarify the discussion.

so explain to me how the source is not the most important?

ya can't shine s**t, my friend

i see your point to a certain extent, but team source first is saying, essentially to quit spending gobs of money on amps and cans when you can start with the source, which in the long run will always be better.

Drew, I see what you are saying and I agree mostly, but I don't see what you are trying to say in the context of the prior discussion. The debate was mostly the difference BETWEEN sources and not the difference of effect between the source and other things in the chain. As far as the source first debate, I think you are confusing source FIRST with source ONLY. Nobody is advising everyone to buy a $5000 source and spend $200 on the whole rest of the chain. They are just saying there's no reason to invest in pricey amps and phones unless you have a source to feed them a signal of enough wuality to make their services worth it.

-Jay

I'm not trying to argue that the source is not important; rather, I am trying to form a basis for a more informing discussion.

What does this have to do with the prior discussion? The orignal question was basically, "is the source important enough to validate my buying this". In the responses, I saw no shortage of opinions and recommendations - but I did see a shortage in validating reasons. Rather than try to explain it, perhaps I should just give an example....this is my opinion, take it for what it is worth:

You should initially spend the most money on your source because your source will have the greatest impact on the accuracy of the rest of the system but the least impact on the subjective quality of your system. In other words, you are less likely to want to buy a new source merely to change the "character" of your system. This is much more easily (i.e. cheaply) done by buying a new pair of headphones or, to a lesser extent, a new amp.

While an amp or a pair of headphones can make up for a "harsh" sounding source, an amp or pair of headphones cannot add the detail that an inaccurate source loses. Get the source right the first time around and do your tuning with the items in your chain that will be the most subjective anyway. For example, I spent $1300 on my source, $600 on my amp and $350 on my headphones and <$50 on my cables.

Now, you may agree or disagree with my opinion, but isn't my reasoning behind saying "source first!" more understandable?

As far as I know, iTunes converts the audio to Apple Lossless, sends the stream to the AX, which converts it back to something more useable. The optical out of the AX is bit perfect as far as I can ascertain. I was going to go the optical out route and try a DAC but am satisfied with the analogue out of the AX and have left it there for the moment (going from my AX to my AMP). Maybe I'll end up getting a DAC1 in the future, because I think it may not be worth getting a DAC with the AX device unless it is a very good DAC such as the DAC1. From what I can tell, you need to turn off some of the sound enhancing options in Itunes to get a bit perfect optical out signal, although I have not confirmed this.

From what I can tell you need to turn off ALL the "enchancing" options to
get decent sound out of iTunes.

I have a CI DAV-1 and there is definitely a difference with the sound output as compared to straight out of the AX. I will add that the sound quality straight out of the AX is not bad either. I've never heard a DAC1 so I can't compare. I need to see if anyone attending the South Florida meet has one to do a comparison.