An analog input voltage (or current) would be sent to device called an analog-to-digital converter (ADC or A/D). It is then converted to a discrete number and either processed or stored.In practical...
Kane kramer is the inventor of the digital auto player and not the inventor of the iPod or the mp3 so don't get confused by that if doing a project about iPod's and mp3's like me and my friend did.
A coaxial digital output (usually an RCA jack) can connect to a digital optical input using a coaxial to optical digital converter. This is a small box that goes in between the two products.
A digital audio jack serves the same purpose as an analog audio jack, only it transmits a signal that is digital (1s and 0s) instead of analog (waveform).