Cepstral

Part of speech: adjective

Definitions

1. Relating to the cepstrum, the inverse Fourier transform of the logarithm of a signal's spectrum, used in speech and audio analysis
2. Describing features derived from a signal's cepstrum, a spectral representation often applied to recognizing speech sounds
3. Of or pertaining to the cepstrum, a technique in signal processing that separates the source and filter components of a sound

Etymology: The word was coined as a playful reversal. In 1963, the statisticians B. P. Bogert, M. J. R. Healy and J. W. Tukey published a paper on echoes in seismic and acoustic signals, and to describe the logarithm of a spectrum's Fourier transform they reversed the first four letters of "spectrum", producing "cepstrum". Their other terms followed the same joke: "quefrency" for frequency, and "liftering" for filtering. The adjective "cepstral" simply adds the ordinary English suffix "-al" to that new noun, modelled on "spectral", which it resembles in shape. The meaning is tied to the way the method treats sound. Analysing a spectrum tells you which frequencies are present, and taking the logarithm and transforming again reveals periodic patterns within that spectrum, such as the repeating echo of a voice's pitch. Because "cepstral" describes features of this second-level analysis, it is used specifically in speech and sound processing.