Ruby and Jules on the radio - what's the quality of the sound?
I believe the answer is:
gemstone
'ruby and jules on the radio' is the definition.
I can't tell whether this defines the answer.
'the quality of the sound?' is the wordplay.
'the quality of' becomes 'gems' (I can't explain this - if you can you should give a lot more credence to this answer).
'the sound?' becomes 'tone' (tone is a kind of sound).
'gems'+'tone'='GEMSTONE'
'what's' acts as a link.
Can you help me to learn more?
(Other definitions for gemstone that I've seen before include "Physical power" , "Jewel" , "It's considered precious" , "Piece of crystalline rock as jewellery" , "Emerald or ruby" .)