That’s not quite right. Impedance changes do not cut out or add. (Well, unless you over-do it.) What it does, electrically, the signal goes down the wire from a source (the cartridge) to the other end (phono stage), where there is an impedance or resistance at each end.
We want the signal to flow smoothly all the way through. But if the impedance is different enough then some of the signal bounces off and heads back, then reflects back again from the other end. This back and forth is what we call ringing and it happens with a lot of other things too. (It is why for instance springs like Townshend Podiums are great under speakers, they eliminate this ringing.)
Changing the impedance loading is like, think of light hitting water. Water is different resistance than air. There is an impedance mismatch. Most of the light goes through but some reflects back and you see it as glare. Wearing polarized sunglasses filters out the glare. That is a filter and is NOT what impedance loading does! Impedance loading takes you under the water to where now there is no glare.
In short then impedance loading improves the sound by eliminating the ringing which is an artifact of mismatched impedance.
We want the signal to flow smoothly all the way through. But if the impedance is different enough then some of the signal bounces off and heads back, then reflects back again from the other end. This back and forth is what we call ringing and it happens with a lot of other things too. (It is why for instance springs like Townshend Podiums are great under speakers, they eliminate this ringing.)
Changing the impedance loading is like, think of light hitting water. Water is different resistance than air. There is an impedance mismatch. Most of the light goes through but some reflects back and you see it as glare. Wearing polarized sunglasses filters out the glare. That is a filter and is NOT what impedance loading does! Impedance loading takes you under the water to where now there is no glare.
In short then impedance loading improves the sound by eliminating the ringing which is an artifact of mismatched impedance.