Back in the early digital days the biggest difference between digital and analogue cable used to be the quality of the copper used, together with the design consideration regarding impedence etc... as identified in the previous posts.
The quality of the copper together with it's design features allows the digital signal to be transmitted "cleanly" i.e. as a square wave at very high frequencies - much higher than the analogue bandwidth.
With digital, it is very important that rise to the top of the square wave, it's duration at the top and it's subsequent return to the zero position creates as close to a square waveform as possible, so that the receiving equipment, e.g. a DAC, can recognize each "bit" of data that is transferred.
Since the advent of digital, the quality of copper used in all cables has improved to the point where "Analogue cables" will work quite nicely when used for digital purposes.
Using Digital cables for analogue will also work extremely well since the bandwidth of digital cables tend to be very high (MHz - GHz) - far in excess of the analogue signal requirements (kHz). However, digital cables can have a higher capacitance/impedence than analogue cables, which can colour the sound.
So what's missing from digital, as implemented in the audio world?...
> When a computer transfers digital information to a USB stick there is a series of checks and balances performed to determine if all the data, in a spreadsheet for example, has been received by the USB stick - if not it is re-sent. After a few failures the process generally issues a warning and halt the transfer.
However, with digital transfers to a DAC (e.g. internet streaming or data from a CD transport), you never know if all of the signal gets to the DAC because the "checks and balances" are not performed and the DAC "fills in" the missing information and still manages to create a very good analogue signal.
So, using an analogue interconnect may sound as though it's working very well, but the DAC is actually making it sound that way.
Using a digital cable will not "guarantee" all the data gets to the DAC either, but the success rate tends to be significantly higher, because they are designed for digital transfers.
My own personal experience with digital cables has proven to me that using a digital cable with the highest bandwidth available (currently using 150mbs) improves the analogue signal from the DAC significantly.
Using highest bandwidth optical cables available also results in significantly better sounding music.
However, I still use analogue cables for analogue signals.
One day the two may converg and we will simply have "interconnects"
BTW - subwoofer cables are designed specifically for extreme low frequncies - you can use a regular interconnect or a digital interconnect, but they won't work quite as well.
