Differential Equations applications in Signal Processing
I don’t think it will hurt or will be a waste of time.

You can think of SP in a number of ways and those ways overlap. It’s a technolgy, a science,a branch of mathematics, an engineering discipline, and your view is largely tied to your self image.

A lot of SP is based on physical models.  A lot is based on hueristics. 

SP overlaps. You might benefit from taking music or statistics. A lot of people take the longer path.

Differential equations are a way to describe a lot of phenomena that SP is used to sense and often control.  

You should consider what motivates you. 

To be honest a lot of what I took had to do with what was offered that semester. Getting that piece of paper on time was a huge practical consideration.