Robertsong, typical CDP used as a transport outputs digital S/Pdif signal with about 25ns edge transitions. Speed of signal in the wire depends on the dielectric but we can assume about 5ns/m. Very start of transition (knee) travels thru cable and reflects on characteristic impedance boundary (impedance change). That is always the case since there is no perfect match but degree of mismatch (and therefore reflection) changes. It will take 10ns for signal to travel forth and back of 1m cable. Reflection will add to transition in progress changing its shape. This will affect moment in time when level change is recognized by the DAC (threshold). Pick 1.5m cable and we're dealing with 15ns until reflection comes back. It will still add but to second half of transition when level most likely will be already recognized. In this application 1.5m cable will be better than 1m cable but, as I said, it might depend on slew rate of the transport (expensive dedicated transports are often faster) plus dielectric and metal used.
This time variation of edges in time is called jitter. Jitter is basically noise in time domain. In frequency domain it shows as small sidebands not harmonically related to root frequency (music tone). Imagine playing 1kHz tone while digital cable is in close proximity of strong 60Hz noise (power cable). This might produce 60Hz jitter of digital signal creating two sidebands (sum and difference) to tone that is being played. One sideband will have frequency of 1060Hz while another will be 940Hz (-50 to -60dB typical). So instead of just single frequency you'll get three. Now play thousands of frequencies (music) and you'll get 3x more. Replace 60Hz noise with combination of many frequencies (radio stations, 60Hz, etc) plus effects of reflections in the cable and you'll get total mess. This mess is noise that is proportional to amplitude of music signal. The only way to detect it is to see effects of it as lack of clarity, less precise imaging, less "black" background etc. Without signal there will be silence since there will be nothing to modulate.
If we won't take into consideration other effects like ground loops created by the cable or noise collected and injected into analog section, then the only difference between digital cables is jitter. Character of this jitter is affected by the character of the noise - is it random (uncorrelated) or caused by offending frequency like 60Hz (correlated), is shield better in suppressing high or low frequencies, are there any reflections in the cable?
One cable might be better characteristic impedance match to your system, while the other might have shield working better at the particular noise present in your room. More expensive cables tend to have better shielding but might be not the best impedance match to your system. Expensive cable doesn't have to be better. Coax is usually better than Toslink having wider bandwidth (hundreds of MHz vs tens of MHz) but when transport transitions are slow and therefore susceptible to noise and this electrical noise is present then Toslink might sound better. There is no right or wrong because it is system dependent. Toslink might be even blessing if you have ground loops.
Now let's get back to our 940Hz, 1000Hz, 1060Hz example. These sidebands are close to 1kHz tone thus masked a little bit more than frequencies further apart. It is sonic signature of sort, related to type of electric interference in your room, system noise, impedance matching, transport slew rate , cable propagation speed, shield effectiveness at different frequencies and perhaps few other I cannot think of now.
Average person using electricity has "idea" about it but very few understand it. Same should be true for digital cable. We have an idea but we have to try it since there is no way anybody can predict or measure how it will sound in particular system.
This time variation of edges in time is called jitter. Jitter is basically noise in time domain. In frequency domain it shows as small sidebands not harmonically related to root frequency (music tone). Imagine playing 1kHz tone while digital cable is in close proximity of strong 60Hz noise (power cable). This might produce 60Hz jitter of digital signal creating two sidebands (sum and difference) to tone that is being played. One sideband will have frequency of 1060Hz while another will be 940Hz (-50 to -60dB typical). So instead of just single frequency you'll get three. Now play thousands of frequencies (music) and you'll get 3x more. Replace 60Hz noise with combination of many frequencies (radio stations, 60Hz, etc) plus effects of reflections in the cable and you'll get total mess. This mess is noise that is proportional to amplitude of music signal. The only way to detect it is to see effects of it as lack of clarity, less precise imaging, less "black" background etc. Without signal there will be silence since there will be nothing to modulate.
If we won't take into consideration other effects like ground loops created by the cable or noise collected and injected into analog section, then the only difference between digital cables is jitter. Character of this jitter is affected by the character of the noise - is it random (uncorrelated) or caused by offending frequency like 60Hz (correlated), is shield better in suppressing high or low frequencies, are there any reflections in the cable?
One cable might be better characteristic impedance match to your system, while the other might have shield working better at the particular noise present in your room. More expensive cables tend to have better shielding but might be not the best impedance match to your system. Expensive cable doesn't have to be better. Coax is usually better than Toslink having wider bandwidth (hundreds of MHz vs tens of MHz) but when transport transitions are slow and therefore susceptible to noise and this electrical noise is present then Toslink might sound better. There is no right or wrong because it is system dependent. Toslink might be even blessing if you have ground loops.
Now let's get back to our 940Hz, 1000Hz, 1060Hz example. These sidebands are close to 1kHz tone thus masked a little bit more than frequencies further apart. It is sonic signature of sort, related to type of electric interference in your room, system noise, impedance matching, transport slew rate , cable propagation speed, shield effectiveness at different frequencies and perhaps few other I cannot think of now.
Average person using electricity has "idea" about it but very few understand it. Same should be true for digital cable. We have an idea but we have to try it since there is no way anybody can predict or measure how it will sound in particular system.