Digital interface

[Dr_simon]

Three questions that are killing me ....

1) Is their any difference in quality between AES-UBU and S/P DIF ? Do the same ideas about balanced and unbalanced cable apply to digital as well as analogue signal ?

2) I have just got a digital patch bay (ST Audio). When I use the optical input to receive S/P DIF coded signal (via an M-audio coax-optical converter) from: Pod Pro, Bass Pod pro or GNX2 and relay it to SONAR, it sounds fine. Connecting any of the above to the patch bay via the AES-UBU also sounds fine. However, if I connect any of the above (using a 75 ohm digital cable) to the patch bay via the S/P DIF coaxial input it sounds dreadful (squeekks, pops, dropouts blurrrg !) . I have checked the cable and it is fine !

I have taken care matched all the output sample rates and bit depths.

I think this bit of kit is broken....or am I missing something.

And......3) What is the impediance of standard Lo-Z mic cable and can it be used to connect AES-UBU devices with out causing them to explode !

Cheers
Simon

 

[Dr_simon]

Ah, well I think I’ve found the answers to my questions and incase any one else is interested I’ll post them.

Impedance:

Digital
S/P DIF likes 75 ohm RCA connections
AES Likes 110 ohm connections

Low Z 150 to 600 ohms
Medium impedance is 1000 – 4000 ohms
Hi Z 25Kilohoms

Practical upshot, digital cable is super low impedance and it is probably better to use the right cable for the right job (even if its just to avoide "loading down" which can cause problems).

As far as I can tell S/P DIF and AES are just as goes as one another providing you stick to the rules i.e. don’t exceed the maximum length for the cables and if you do, use a router.

As for the digital patch bay, well it went back to musicians friend for an exchange.