I haven't read all the responses, so this may be redundant.
When a cable's insulation changes (due to exposure to humidity/high temperature/contact with liquids, etc.), the cable's impedance changes. For example, airplane mechanics can tell whether a wire has been damaged due to exposure to humidity or hydraulic fluid just by measuring the impedance of the wire. In fact, they can tell not only whether a cable has been damaged, but also the starting point, length, and type of damage, just by measuring the impedance. Obviously insulators that resist environmental effects can reduce the problem.
The impedance changes are observable in the audio-frequency spectrum. So the impedance characteristic of the wire affects the signal and the sound.
Does this lower the sound quality? I don't know. Perhaps it makes it better.
When a cable's insulation changes (due to exposure to humidity/high temperature/contact with liquids, etc.), the cable's impedance changes. For example, airplane mechanics can tell whether a wire has been damaged due to exposure to humidity or hydraulic fluid just by measuring the impedance of the wire. In fact, they can tell not only whether a cable has been damaged, but also the starting point, length, and type of damage, just by measuring the impedance. Obviously insulators that resist environmental effects can reduce the problem.
The impedance changes are observable in the audio-frequency spectrum. So the impedance characteristic of the wire affects the signal and the sound.
Does this lower the sound quality? I don't know. Perhaps it makes it better.