Apparently, audioquantize was already designed with C89 in mind. However, one small issue still slipped through the net:

#define A() int i;
#define B() int j;

when used like this:

{
  A();
  B();
...
}

leads to

{
  int i;;
  int j;
...
}

Unfortunately ; already comprises an instruction which may not be followed by further variable declarations. Patch attached.