with #include <cmath>:

src/analyserwaveform.cpp:211:44: warning: narrowing conversion of '(double)__builtin_abs(*(buffer + (sizetype)((long unsigned int)i * 4ul)))' from 'double' to 'CSAMPLE {aka float}' inside { } is ill-formed in C++11 [-Wnarrowing]
         CSAMPLE cover[2] = { fabs(buffer[i]), fabs(buffer[i+1]) };