[Technical Question] SPDIF C Chammel on NDX

Simon,  I've flagged this for Phil, but he may have a sore head today after Naim's Christmas party yesterday.

Hi Simon,

Only just seen this which is odd as I check the forums every few days for stuff that has been punted over to me - anyway, the BNC output is S/PDIF.

Cheers

Phil

Hi Phil, thanks, are able to say what C channel control word bits you set please. In addition can you advise what sample rate bit setting Naim use in the C [control] channel for above 48kHz. if it varies by device, from the NDX please. Appreciate your help as I have no C channel SPDIF analyzer.

Simon

On external inputs 'C' channel data is echo'd from input to SPDIF output.  

On internal feeds,  byte 3, bits 24-27 wil be either 0 (for streaming sources) or 1 (for FM/DAB). It is unsafe practise for any DAC to read the C data to obtain the incoming sample / data rate. It should be measured instead.

Phil

Thanks - and I assume byte 1, bit 0 is 0 (Consumer)?

Simon

It should be, yes...

...can I ask why you're asking?

Phil

Phil

It appears there are a few DACs that seem to struggle with ndx output as a few have reported on the forum.  What we know now is that if an external spdif source passes through the NDX then it cant be anything to do with C channel bits.

Also in some circles, a BNC is used for AES and RCA for SPDIF, but you have indeed confimed despite BNC use the output is indeed SPDIF and uses consumer C channel settings.

Thanks

Simon

Hi Simon,

The forums aren't really the best place to be trying to resolve interoperability issues - the "forum noise" tends to get in the way and it's easy to start barking up the wrong tree with everyone rushing off in teh wrong direction - overall it's not really an effective way of doing that kind of thing and the route for such support should be through the Naim support channels, either myself or Steve Hopkins.

In this case there shouldn't be any issues with the latest 3.9 codebase ... as far as I am aware it was possible in the earlier code for the mute bit in the S/PDIF stream not to be lifted - this should now be fixed - if there are still issues then those affected should really be talking with us. (Not that I'm trying to stop you helping anyone - just that it really needs to be something that we look into as the manufacturers.)

We use BNC connectors for S/PDIF because they are a 75ohm impedance connector and provide a far better connection than phonos - which is what S/PDIF ideally requires - nothing to do with AES. Most "high end" phonos that are pleasingly chunky concentrate on the ground contacts (which is what the customer sees and feels) rather than the actual signal contact (which on a typical phono plug / socket interface is dissapointingly poor) - so for us the better connector for S/PDIF is BNC, just as for us the better audio connector is the DIN connector.

Hope this helps.

Cheers

Phil

Thanks for the insight.. yes getting the balance on the forum must be a tricky one. I think there is a good range of technically aware/professional engineering  people on here from various disciplines and so occaionally we can get some stimulating discussion, and I suspect when the language or thinking gets a little too technically involved, many switch off who can't follow which is probably no bad thing to avoid the pitfalls you outline.

However despite that if someone can't get thier Naim to work surely they would be unwise not to contact Naim support directly.

Simon

You'd think so wouldn't you?

Phil