Let’s say you have a CD player and a power amplifier, between these two do you have a dual pot to both positive and negative signal wire, no grounding at all. Or you could say a variable resistor in the middle of the cable.
Would the variable input resistance do anything negative?
Or should the impedance be constant even under change in the attenuators resistance?
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As you describe it, you’d be degrading the performance of your audio system.
In an ideal audio system, you have a voltage divider where the impedance of the cable is zero and the impedance of the audio equipment is infinite. This yields a situation where all of the power of the system is in the audio equipment and none of it is in the cable.
What you’re doing with your variable resistors is increasing the impedance of the cable, reducing the amount of power that is delivered to the audio equipment. You’re also going to be introducing noise into your signal (potentiometers are fairly noisy components even above the fact that you’re setting up a bad voltage division).
If you’re trying to implement a volume control, the general rule is that you adjust the signal where it is most powerful rather than where it is least powerful because low power signals are far more subject to noise.
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