I think one reason for this may be that Roger Waters is at least somewhat tone-deaf (he seems to be--I heard him do an acoustic demo of Bravery of Being Out of Range, and the time it took him to realize he was way off key makes me think he's probably tone-deaf). Which I'm sure then made it an absolute nightmare for Mr. Gilmour to try to sing harmony, as well.

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"And with these words I can see
Clear through the clouds that covered me
Just give it time then speak my name
Now we can hear ourselves again..."

WrightSatellite #1