bearing opsignal → tableimport fullseye as fs; fs.ledger.cepstrum(x, rate, mode='real', floor_ratio=1e-12, min_quefrency=0.0) (実装を直接呼ぶなら import acoustics; acoustics.cepstrum(x, rate, mode='real', floor_ratio=1e-12, min_quefrency=0.0)、台帳から引くなら opsacoustics.get("cepstrum"))The spectrum of the log spectrum — periodic structure in frequency.
A harmonic family or a family of modulation sidebands is periodic along the
frequency axis, so it collapses to a single line along the cepstrum’s
quefrency axis (in seconds). Two things this finds that a spectrum does not:
an echo at delay tau (a rahmonic at q = tau) and a sideband
family spaced df apart (a rahmonic at q = 1/df). The second is the
bearing case — sidebands around a gear mesh spaced at the shaft rate.
mode:
"real" — irfft(log|X|), the standard real cepstrum. Discards phase,
so it cannot be inverted; nothing here pretends otherwise."power" — irfft(log|X|**2) = 2 * real, kept because the two
conventions differ by exactly a factor of two and mixing them silently
halves or doubles every amplitude a caller compares against a reference.log(0) is handled by flooring the magnitude at floor_ratio times its
own maximum (default 1e-12, i.e. -240 dB) rather than letting -inf enter
the inverse transform, where it would make the entire cepstrum NaN. The
number of floored bins is returned as floored_bins — a large count means
the signal is band-limited and the cepstrum is dominated by the flooring, not
by the signal.
min_quefrency (seconds) excludes the low-quefrency region from the peak
search. This is not cosmetic. The first few bins carry the spectral
envelope — the overall shape of the spectrum, which is large and has
nothing to do with periodic structure — and they dominate. Measured on an AM
tone with sidebands 50 Hz apart, the five largest cepstral values sit at
0.000125, 0.00025, 0.000375, 0.000625 and 0.001 s, i.e. all of them are the
envelope, and the default peak search returns 0.000125 s rather than the
1/50 = 0.02 s a reader would expect. Excluding the envelope is the standard
practice (“liftering”) and is the caller’s decision, so it is an argument
with a visible default of 0.
Returns a dict: quefrency (s), cepstrum, rate, mode,
floored_bins, min_quefrency, peak_quefrency, peak_amplitude,
peak_rate_hz (1/peak_quefrency — the sideband spacing or repetition
rate the rahmonic corresponds to). The peak is taken over
min_quefrency < q < n/(2*rate); the cepstrum is symmetric past that.
Measured ground truths:
peak_quefrency = 0.025000 s, peak index exactly 200, and
floored_bins = 0.0.020000 s = 50.00 Hz exactly, with
min_quefrency=0.002.mode="impulse" bearing signal repeats every 1/107 s, and the largest
rahmonic above 2 ms is at 0.037383 s — which is 4/107, the fourth
rahmonic, not the first. A cepstrum reports a family, and reading only
its maximum gives an answer that is off by an exact integer factor and
looks entirely reasonable.mode="power" is exactly twice mode="real" (measured max difference
0.000e+00).
Raises ValueError: everything :func:_as_signal refuses, an unknown
mode, floor_ratio outside (0, 1), a negative min_quefrency, a
min_quefrency at or past the half-length of the record (nothing would be
left to search), an identically zero signal, and a signal shorter than 4
samples.
py -3.11 examples/acoustic_condition_monitoring.pypy -3.11 examples/poc_web_roll_periodicity.pytable を入力に取れる)bearing)envelope_spectrum · bearing_defect_frequencies · spectral_kurtosis
Provenance: acoustics.py — ACOUSTICS operator registry. この per-op ノートは tools/opdocs.py md が自動生成(手編集しない)。
© 2026 Kazufumi Furuse — Fullseye operator documentation. Licensed under Apache-2.0.