G.723.1 is a fixed-point codec. So you may notenable FZM and can't expect any benefits if it enabled.
The same true for fixed-point version of the G.729 codec.
As for floating-point version of the G.729, you can expect denormals during encoding. Their appearance depend on input data (for example large enough zero block after non-zero data).
The default codec operation mode is precise. To build codec with fast mode enabled you should add define CLIPPING_DENORMAL_MODE to the USC library makefile.
Igor S. Belyakov