Quefrency is a human-made variable introduced with cepstral analysis to name the independent axis of the cepstrum — it measures periodicity in a frequency spectrum, expressed as a 'reverse time' whose units match those of the original domain (e.g., milliseconds). It is not a physical time but a computational abstraction: the value on the quefrency axis at which the cepstrum peaks indicates the spacing (in the original domain) between spectral harmonics or resonances. The cepstrum was invented by Bogert, Healy, and Tukey (1963); the term quefrency is a portmanteau of 'spectrum' and 'frequency' (suffix -queincy echoing -ency) to signal that it is the dual-domain counterpart of time in Fourier analysis, with the name chosen so that 'time' in quefrency reads back as 'frequency' in the original domain. [formal: quefrency | substrate: mind | horizon: a moment | explicit: yes | epoch: 0.01]
Accepted ontology entry
quefrency
Quefrency is a human-made variable introduced with cepstral analysis to name the independent axis of the cepstrum — it measures periodicity in a frequency spectrum, expressed as a 'reverse time' whose units match those of the original doma…
Definition
Why it is in scope
The independent variable of a cepstrum analysis, representing time-like delay in the quefrency domain; the term is a back-formation from 'frequency' to indicate that cepstral analysis operates on a transformed time axis derived from the logarithm of the power spectrum.
Names and aliases
- quefrencyen · CANONICAL
Relations from this entry
- cmspjfefp05lxjlssg1w6gyuvDERIVED_FROM →
Quefrency is the back-formation variable of cepstral analysis. The concept of the cepstrum existed first and gave rise to the quefrency domain — cepstrum fed into quefrency.
- cmspjfefp05lxjlssg1w6gyuvDEPENDS_ON →
Quefrency is a concept that exists solely within the framework of cepstral analysis. It is the variable name used to describe the cepstrum's independent axis. Remove the cepstrum concept and quefrency has no meaning — it is the dual of frequency defined only in reference to the cepstrum. This passes the removal test.
- cmrvsdf2u027u2ceisomaun7qINSTANCE_OF →
Quefrency is a specific kind of variable — it is a named variable in the cepstrum domain measuring 'reverse time.' A competent speaker would call quefrency 'a variable.'
- cmspqokmf0684jlss24yd0c6fDEPENDS_ON →
The concept of quefrency was invented by Bogert (1963) within the framework of cepstral analysis and has no operational meaning outside it. Remove cepstral analysis and quefrency ceases to operate — there is no independent use for the quefrency concept. This is constitutive: quefrency is defined by its role within cepstral analysis.
Relations to this entry
- cmspmjaky05vwjlss1p9r2wo0← DEPENDS_ON
A cepstral coefficient is a numerical value at a specific quefrency point. Remove quefrency as the indexing dimension and the coefficient loses its positional meaning — it cannot operate as a coefficient without the quefrency axis that gives it a coordinate.
- cmsqjg9e8003rnqh9rlrvkyjt← DEPENDS_ON
Liftering operates in the quefrency domain: it applies a smoothing filter to the cepstrum (the quefrency representation of a signal). Remove quefrency — the concept of quefrency — and liftering has no domain on which to operate. This is a constitutive, present-tense dependency, not a meta-level claim about language.
Record identity
- Created
- Aug 12, 2026, 4:43 AM UTC
- Content hash
- b68079970ab1671763297e39a3af48d6cf6d1f6e7d86ba7e4f9b7696ba6717fa