Digital Cables

Sounds like nonsense, there are a bunch of electrons traveling through a wire and electrons don’t now if they are 'analog' or 'digital'. In fact, all electrical signals are analogue.
However, the digital signal is different, it is a pulse train, a square wave in stead of a sine.
As everything is finite in our universe, square waves don’t exist.
Transition from logical 1 to logical zero is a matter of going from e.g. 4V to 0V and this requires time.
There is always a rise/fall time and the edges will be rounded. This generates a series of harmonics of the base frequency. Our square wave is a kind of trapezium with rounded edges.

Traveling through the cable, the shape will change. If this change becomes to big, the receiver will not be able too reconstruct the logical 1’s and 0’s properly.

Depending on the characteristic impedance of the cable, the capacitance of the cable, and the impedance match between the source and load devices, the corners of the square wave will round off to a greater or lesser degree, and the "flat" portions of the wave will become uneven as well. This makes it harder for the receiving circuit to accurately identify the transitions and clock the incoming signal. The more degradation in the signal, the harder it is for the receiving device to accurately measure the content of the bitstream.

Blue Jeans Cable

If you need to connect to devices ‘digital’ you better use a cable in accordance with the specifications.This is a matter of having a cable with the right impedance with little variation over the relevant frequency range.

SPDIF needs a 75 Ohm cable, AES/EBU 110 Ohm, etc.

You can’t measure this impedance using a conventional volt-ohm meter.
Well you can but you will measure something close to zero.
This is the DC impedance

These standards refer to the characteristic impedance.
This is the AC impedance of the transmission line and is defined as:

L=inductance per unit length
C=capacitance per unit length

In practice, as digital signals are pretty robust, using an 'analog' cable, might work as well.

Quarter wavelength

A rule of the thumb is the quarter wavelength. If the analogue cable is shorter then ¼ of the wavelength, it will probably work.
An example:
Using the AES/EBU protocol to connect to devices playing Redbook audio.

Sample rate	44100	Hz
Word length	24	Bit
Channels	2	Stereo
biphase-mark-code	2	Twice the sample rate

Frequency	4233600	Hz (SRBitChannel* biphase)
Light speed	3*10E8	m/s

Wavelength	70,9	m (speed/freq)

Divide the wavelength by 4 and approximately 17 m ‘analogue’ cable might do the job.