The pfft~ object is designed to simplify spectral audio processing using the Fast Fourier Transform (FFT). In addition to performing the FFT and the Inverse Fast Fourier Transform (IFFT), pfft~ (with the help of its companion fftin~ and fftout~ objects) manages the necessary signal windowing, overlapping and adding needed to create a real-time Short Term Fourier Transform (STFT) analysis/resynthesis system.
The number of inlets on the pfft~ object is determined by the number of fftin~ and/or in objects in the enclosed subpatch. Patchers loaded into a pfft~ object can only be given signal inlets by fftin~ objects within the patch. See fftin~ and in for details.
Name of patcher to load
Specifies the FFT size, in samples, of the overlapped windows which are transformed to and from the spectral domain by the FFT/IFFT. The window size must be a power of 2, and defaults to 512. (Note: The size of the spectral "frames" processed by the pfft~ object's subpatch will be half this size, as the 2nd half of the spectrum is a mirror of the first and thus redundant, unless the full-spectrum-flag is present.)
overlap-factor (hop-size-denominator) [int]
The third argument determines the overlap factor for FFT analysis and resynthesis windows. The hop size (number of samples between each successive FFT window) of Fast Fourier transforms performed is equal to the size of the Fast Fourier transform divided by this overlap factor. (e.g. if the frame size is 512 and the overlap is set to 4 then the hop size is 128 samples). The value must be a power of 2 and defaults to 2. A value of 4 is recommended for most applications.
The fourth argument specifies the start onset in samples for the Fast Fourier transform. It must be a multiple of the current signal vector size and defaults to 0.
full-spectrum-flag (0 or nonzero) [int]
A non-zero fifth argument may be used to specify "full-spectrum mode". In this mode, the pfft~ object will internally compute a complex FFT and process full DC to SR mirrored spectra (instead of simply eliminating the redundant half of the spectrum). This takes extra computing power but may be potentially useful in some of the more esoteric spectral processing applications.
'args' and list-of-argument-values [symbol]
Use the argumentfollowed by an argument value to initialize any pound-sign arguments in the loaded patcher (e.g., ). If used, the argument must be the last argument word used; everything which appears after the word will be treated as an argument value.
Common Box Attributes
Any messages received by an out object in a loaded patcher appear at the message outlet of the pfft~ object which corresponds to the number argument of the out object. The message outlets of a pfft~ object appear to the right of the rightmost signal outlet.
The output is the result of the FFT-based signal processing subpatch. As with the fft~ and ifft~ objects, pfft~ introduces a slight delay from input to output (although it is less than half the delay than with an fft~ / ifft~ combination). The I/ O delay is equal to the window size minus the hop size (e.g., for a 1024-sample FFT window with an overlap factor of 4, the hop size is equal to 256, and the overall delay from input to output is 768 samples). The number of outlets is determined by the number of fftout~ and/or out objects in the loaded subpatcher. Patchers loaded into a pfft~ object can be given outlets by fftout~ or out objects within the patch. See fftout~ and out for details.
|Spectral Processing||Spectral Processing|
|Sound Processing Techniques||Sound Processing Techniques|
|MSP Analysis Tutorial 3: Using the FFT||MSP Analysis Tutorial 3: Using the FFT|
|MSP Analysis Tutorial 4: Signal Processing with pfft~||MSP Analysis Tutorial 4: Signal Processing with pfft~|