Can you explain the Certain Proportion part

[trade74]

In your statement:
"A question that can be asked would be: given two signals A and B, what would a third signal M look like if it must resemble both signals in a certain proportion?"

What is the "certain proportion" part? what are you referring to?

[Gagniuc]

The proportion refers to the distance, i.e. to the value of the variable d. You can also look at this post, it may be more useful:
On How to Mix Two Signals by using Spectral Forecast