< mathematics > (Coined in a 1963 paper by Bogert, Healey, and Tukey) The Fourier transform of the log-magnitude spectrum:
fFt(ln( | fFt(window . signal) | ))
This function is used in speech recognition and possibly elsewhere. Note that the outer transform is NOT an inverse Fourier transform (as reported in many respectable DSP texts).
[What's it for?]