Have your say & ask the experts

I can;t be bothered reading all these lengthy posts, ask me a proper question and I'll give you an answer.

Why is water wet?

Thanks guys, a very informative thread and very well explained by all.

Now what on earth do you expect me to do with that information ?

(Hunts for box marked ' Info to use  if ever unfortunate to get stuck in conversation with old science teacher at school reunion'....Ah here it is. Oh it's empty !)

What on earth happened there. This site gets more messed up everyday

Well, you know, I just started with the odd bit of useful data here and a byte of interesting binary there but then it wasn't enough.  Before too long, I was scouring forum after forum just looking to shoot up any useless or trivial feeds.

Mine is a cautionary tale:  Remember kids - don't do digital.

andyb190:

What on earth happened there. This site gets more messed up everyday

Cheers Andrew,

Don't suppose you can 'allow links/images' on my account as well could you ? 

Gozaradio:

Mine is a cautionary tale:  Remember kids - don't do digital.

Yep, too many dac heads... it's a Cyrus problem ! 

I really enjoyed this thread. Thanks very much for a real explanation of how CD data is read and transmitted.

I think the manufacturers have a lot to answer for here. It's clear that when CDs were invented, as an audio storage standard, the CD contains all the data it needs to ensure an error free read can be made. So what excuse do manufacturers have for not properly utilising this and how on earth can they excuse making equipment that doesn't broadcast an accurate bitstream from a CD?

It's a shame that What Hi-Fi don't take up the cause and get a little technical on our behalf. Rather than rating £30k CD players as the best in the world ever, they should be asking why your £200 is not buying a fault free digital read from a disk. What are they spending the money on?

A clear co-axial digital or a clear optical signal should contain as much data as is possible from the disk. Considering how much of this data is meant for error correction and time sequencing (over half from the sound of it) there is NO EXCUSE for the DAC to not reconstruct a perfect analogue sound wave.

Normally I'd say the system should have the ability to ask the transport to check the data. Digital outputs from CD players are one way only but there should be plenty of information in the stream for it not to be necessary to go back and ask again.

So What Hi-Fi, can't you use your influence to get an explanation out of manufacturers as to how they seem to engineer such difference into CD players? It's almost as if they're purposefully sabotaging the technology, that should be fairly faultless at a low cost, just to create an expensive hierarchy of CD players and make the consumer pay more.

Be very interested to hear WHFSV's views and others here. Great thread. (Sorry about this turning into a bit of a rant!)

Will Harris:

It's clear that when CDs were invented, as an audio storage standard, the CD contains all the data it needs to ensure an error free read can be made.

I'd say more or less the opposite - it's pretty obvious that when they designed CDs, they knew they WERE NOT going to get anything like a clean read in most cases. That's why there's so much error correction designed in, with the fallback of interpolating. We're talking mass produced lumps of cheap plastic with microscopic bumps in, which may have pressing errors, scratches, fingermarks, may be at a constantly varying distance from the read head, with a hole that may not be in the exact centre. It NEEDS all that error correction to achieve a usable end result :-). It's designed to survive a lot of errors; that's because it expects to get almost that many. So it's not too surprising that high end players could track and recover the signal from the CD better than cheaper ones - but even then, I'd expect the CD itself to have errors. 

Will Harris:

the technology, that should be fairly faultless at a low cost

I think you've hit the nail on the head here - it IS _fairly_ faultless at low cost. That's not the same as _completely_ faultless; it just means that almost all of the time cheap players won't get so many uncorrectable errors that you'll hear an obvious click after interpolating the missing samples. And don't forget that when it first came out, there weren't any cheap players...  

Jerry I agree with you. That is so well put!

Isn't it extraordinary though, that after 26 years of having CDs around, they still can't cheaply and reliably, read the disk and correct any errors such that a £100 player sounds different from a £10,000 player. What on earth is going on inside the high end players, and what on earth is it that £100 can't buy you in 2008!!!

jerryC:

I'd say more or less the opposite - it's pretty obvious that when they designed CDs, they knew they WERE NOT going to get anything like a clean read in most cases. That's why there's so much error correction designed in, with the fallback of interpolating. We're talking mass produced lumps of cheap plastic with microscopic bumps in, which may have pressing errors, scratches, fingermarks, may be at a constantly varying distance from the read head, with a hole that may not be in the exact centre.

JerryC, I think you missed the whole point about CDs.. CD information is stored in digital format, the error correction is to make sure that you've read all 0101010 correctly and it has nothing to do with the music. What you're talking about is true for old fasioned black analog disks. The quality on CD depends how it was converted to digital format in the first place in the music studio.

But anyway what in your opition is the best storage for music? A better alternative to digital format (either CD or HD).

Gozaradio:

The way I've been reading this thread, I think that the original question has been a little misunderstood.  I understand OP to be asking something tantamount to 'If you have a £50 CD player with SPDIF out and a £500 CD player with SPDIF out, surely there should be no difference in what comes out of the SPDIF socket'

Just to clear things up, my question was that if you have CD (CD player), HD (Sonos, Squeezebox, etc) and this device has digital out which you connect to external DAC (same in all cases) why would the sound quality be different?

I would hope that the difference in quality between £50 CD player and £20k CD player is the DAC and other components that convert digital signal to analog, but this question is just simple dealing with digital only, no analog conversion.  

The reason I asked this question is because all over the place on the internet I hear ppl saying that Sonos is better than Squeezebox then other ppl say opposite etc.. of course when they use digital out because I'm sure that analog will be different, but I'm trying to understand why would digital be different.

Re the CD error correction and checksum bits that have been mentioned.

This sort of technology is normal with lots of digital information transmission systems. It is designed to allow fault free transmission of information.

If you remember back a few years then PC operating systems were deployed on CD's PC's used exactly the same read heads, disc transports and error correction as audio CD players so you can't say that they are that error prone as a system if they can accurately transmit the whole of a PC operating system. Remember that here any interpolation of data would probably not be acceptable. Also the read rates are far far higher than used for audio CD. I don't think you can buy a CD drive for a PC anymore and plain old DVD drives are getting harder to find but those that are still available can be had for peanuts. In a lot (not all) of cases this is the same technology used inside the transport of most CD players. Given this you must be paying for the quality of the DAC in high end players.