INSTRUMENT design – Fast Fourier Transform (FFT) object
Offt is a utility object that encapsulates several Fast Fourier Transform (FFT) operations for use by RTcmix instruments. These include the allocation of a buffer for the transformation of samples as well as functions to perform a forward- (real-to-complex) or backward- (complex-to-real; inverse) transform on the data in the buffer.
Using the Offt object requires a little basic knowledge of how the Fast Fourier Transform operates. Julius O. Smith has a good math tutorial about the FFT, and the FFTW page is probably the best source of FFT information currently on the web.
The specific FFT code used by the Offt object depends upon how RTcmix was compiled. The default compilation uses older code written by Laurent de Soras (available at musicdsp.org and other places). If RTcmix was compiled using the “–with-fftw” flag during configuration, then the FFTW v. 3 library is used. [note: the FFTW library needs to be compiled with the “–enable-float” flag to work in this object.]