Complex number support is important for a nontrivial niche, but it is nevertheless a niche. Good complex number support is rare, and really it’s only recently that even a few of the more mainstream languages have gotten decent support (e.g. C99). Usually you can work around it, but in the case of Java it’s just not worth it unless you have other motivations for using Java.

If Clojure could have complex number support with nice syntax and semantics that used Java Arrays underneath, it would not be blindingly fast but it would perhaps be sufficient. I don’t hold my breath though, because it’s not really Clojure’s fault. Complex numbers really need to be supported by the math library for this to be really useful, so functions like `exp()` would need to support it for it to work really well.

Incidentally, I’m using Octave for my research. MATLAB is as funky a language as you could ever dream up, but it has all the right stuff for DSP and a lot of other mathematics, which many other languages (and most GP languages) simply don’t.

That said, it’s likely that the vast majority of DSP code in the real world (which is primarily on embedded systems) is written in assembly and C, and have been for years.