Why would one digital ouput have different quality that another digital ouput?

[madeinstein]

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.

 

[Anonymous]

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.