Tutorials and Topics - Peabody Computer Music

Tutorial 26Frequency domain signalprocessing using pfft~You can easily convert between real/imaginary pairs and amplitude/phase pairs using theobjects cartopol~ and poltocar~:Cartesian to polar conversionTechnical detail: The amplitude values output by the left outlet of cartopol~depend on the amplitude of the signal you send to the pfft~ object. Due tothe way fftin~ and fftout~ automatically scale their window functions (inorder to maintain the same output amplitude after overlap-adding), themaximum amplitude value for a constant signal of 1.0 will be(FFT size / (sqrt(sum of points in the window/hop size))So, when using a 512-point FFT with a square window with an overlap of2, the maximum possible amplitude value will be roughly 362, with 4-overlap it will be 256. When using a hanning or hamming window and 2overlap, it will be approximately 325 or 341, and with 4-overlap, it will be230 or 241, respectively. Generally, however, the peak amplitudes in aspectral frame will most likely be only one-fourth to half this high for nonperiodicor semi-periodic “real-world” sounds normalized between -1.0and 1.0.The phase values output by the right outlet of cartopol~ will always bebetween -π and π.211