Locsig's third argument should be the floating point value you want to output at the given sample, so in ( locsig loc i f ))) "f" is the file descriptor returned by open-input -- it is a sort of pointer to the file that you can use with readin or ina to get particular samples. The samples are then what is passed to locsig. So ( locsig loc i (ina i f))) might be closer to what you want.