Form Java and realtime signal processing a paradox?

Should one use C++ instead of java?

The basic idea is this:
1 get a sound into the comp (mic)
2 convert A -> D
3 do something with this (this part should be real fast)
4 convert D -> A
4 get it out (loudspeaker)

point 3 could be written n a low level language
linked to Java. These small code fragments do
the actual sound calculation but are managed
by the (slower) java application

how realistic is this?