What is the best digital source

[rik]

1. Wireless AIR
2. Ethernet RJ45 AIR
3. USB
4. Optical Toslink
5. Optical Toslink mini
6. RCA S/PDIF
7. XLR AES/EBU
8. HDMI

Are there any technical reasons why, at the Devialet socket, these should be different?

Yes.

It depends on who controls the flow of data and hence the clocking. Also the input's ability to reject errors also needs to be taken into account - and I guess if that input injects electrical noise into the Dev' then will sound worse.

Inputs 4..8 are 'push' inputs and will be clocked by the source (CD player, TV, PC etc) so will be completely dependent on the quality of clock provided by that source - Garbage In, Garbage Out etc. If you had a fantastic CD player then you would hope to get excellent results (Also jitter will be source dependent).

Inputs 1..3 (USB only if Async drivers) are 'pull' inputs. The Dev's will decide when it wants the next chunk of input and is probably buffering internally. There is scope and input errors to be re-read[1] and all clocking / jitter will be handled by the Dev'. There is an argument that AIR over Wi-Fi may sound slightly worse as it requires a Wi-Fi chipset to be enabled within the Dev' but they no doubt have this will isolated.

All other things being equal I would expect that USB is the 'best' input but it is very difficult to construct a valid ABX test to prove this.

Rik - but what do I know..

[1] The Dev' uses 'unreliable' UDP/IP for audio input BUT has a X.25 like sliding windows to allow it to correct for any errors. So this will (or SHOULD) not be a problem.