It controls the impedance of the signal running through the cable and keeps it stable. Passive preamps are notorious for sounding thin in the bass and mid bass because they can't control these impedance fluctuations.
Uh, sort of. The impedance of cables and input impedance of an amp is a fixed value. It is not fluctuating and it is not controlled. For the record passives sound thin when they are used with the wrong cables and amps. Mated with the right stuff they sound glorious. Blaming a passive for thin sound is like using salt in a recipe that called for sugar and concluding that salt is an inherently poor ingredient. I'm sure the EAR will work very well in some systems and not so well in others just like any other component in a system.
That's all I've got to say since you can search the archives and find endless debate on the topic.
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