I really don't agree with the question. It's asking for too much.
"...This would require dynamic memory allocation. How would Erlang help me make sure that this allocation does not delay my audio computation?".
It's unlikely that tools exist (in Erlang or any other language) to give you this assurance in advance.
A method that has always been used is timing tests or benchmarks.
If you want to prove that your code will not delay your audio computation, you will probable need to construct this proof yourself. But steps in the proof might rely on previous timing tests.
