ProTools Audio Media 3 Multi track recording question, I get no signal going into S/PDIF inputs. Options

[Seabass]

I want to do multi track live recording on Pro-Tools.  So, I'm cool with the RCA inputs.  But when I try and put regular RCA's into the S/PDIF slots, I don't get a signal from the #1/3 and #1/4 I/O interface selections and they're not bold like the #1/1 and #1/2 ones are.  

Do I need a special S/PDIF chord?  Does my sound source need to go through a digital optical device? Do I have to do something different in my I/O set up?

Thanks.

Are you asking if you have to input a digital signal into your digital input then the answer is 'yes'. For instance, the S/PDIF digital output on a DAT or ADAT machine (both left and right go down the same cable). Regular RCAs work with that.

An analog signal will hit a dead end in the S/PDIF port.

[Seabass]

Thanks for the reply.

So, what do I do if I want a live instrument like a keyboard, mic or guitar to go in my S/PDIF input? Are there digital devices that can be used between the sound source and the sound card in a live setting? And can I use both S/PDIF connectors as separate inputs, or are they just 1 in 1 out?