Bad (or wrong) connectors are the main reason for signal quality loss.

Since every cable is implicitly a 'low-pass' (or better 'high-cut') filter it has an obvious impact on overtones in a signal transmission. But it is the overtones that determine the sound characteristics of any sound source. A precious Stradivari violin does not cost 10 million dollars since it far over 300 years old. It costs that amount, because of its overtone spectrum that it produces from this aged wood.

In the article "Good cables, bad cables ..." I focused on the cable material itself. This article puts the focus on the connectors of a ready-made cable as it is sold by stores and/or manufacturers ... and there two connectors per cable - one on each end ...

 

The surface material of the contacts has the most impact on the so-called 'transition resistance' which is the resistance of the contact spot where the contact of the 'socket' meets with the 'pin'.

For the small-signal path in a pro-audio application this 'transition resistance' should be as low as possible for obvious reasons.