[linux-audio-user] External DAC for mastering use?

Anahata anahata at treewind.co.uk
Tue Mar 23 06:39:00 EST 2004

On Tue, Mar 23, 2004 at 10:27:02AM +0000, Daniel James wrote:

> Currently its about 18 miles away, but I might convert a building in 
> the garden for recording purposes. Do you know what the limitations 
> on the length of S/PDIF cables are?

http://www.epanorama.net/documents/audio/spdif.html :

S/PDIF (IEC-958) uses 75 ohm coaxial cable and RCA connectors. 75 ohm
coaxial cable is inexpensive, because it is the same cable as used in
video transmission (you can buy a video cable with RCA connectors to
connect you S/PDIF equipments together). Coaxial S/PDIF connections work
typically at least to 10-15 meter distances with good 75 ohm coaxial

[Optical TOSLink]
Because high light signal attenuation in the Toslink fiberoptic cable,
the transmission distance available using this technique is less than 10
meters (with some equipments only few meters). 

I wouldn't normally do your Googling for you, but I was quite interested
in the answer myself :-) 

That link also mentions the AES/EBU standard, which uses the same
signal timing but higher levels and will therefore travel greater
distances:  "AES/EBU signal transmission work for few tens of meters with a
good cable." - The cable has to have 110 ohm characteristic impedance.

I'm also interested in the possibility of feeding S/PDIF over structured
cabling using CAT 5 cable. Has any one tried this? I wonder how far it
would go with suitable impedance conversion. 50/75 ohm transformers
would also give electrical isolation.

anahata at treewind.co.uk       Tel: 01638 720444
http://www.treewind.co.uk    Mob: 07976 263827

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