order op• Data kinds: signal → table
• Call: import acoustics; acoustics.angular_resample(x, rate, rpm, samples_per_rev=64) (or opsacoustics.get("angular_resample"))
Resample a time record onto the shaft-angle axis (computed order tracking).
Under a changing shaft speed, a component locked to the shaft has a moving
frequency and smears across the spectrum, while a structural resonance stays
put. Resample the record so the samples are equally spaced in shaft angle
instead of in time and the situation reverses exactly: the order becomes a
single line and the resonance smears.
`rpm` is either a single number (constant speed — the transform is then a
pure rescaling) or a per-sample array on the same clock as the signal. The
cumulative revolution count is the trapezoidal integral of `rpm/60`, and
the signal is linearly interpolated onto a uniform grid in it.
Returns a dict — an angle-domain record is not put into circulation as a
plain signal, deliberately. Its samples are indexed by angle, not time, so
handing it to any op that takes a `rate` would produce frequencies in Hz
from an axis measured in revolutions: no exception, no NaN, just wrong
numbers. (Same judgement, and the same reason, as `motionmag.motion_magnify`
not exposing a bare video adapter.) The dict carries `signal`,
`angle_rev, samples_per_rev, revolutions` (total),
`whole_revolutions, rate` (the original time-domain one, for
provenance), `mean_rpm, max_order`.
`max_order is samples_per_rev / 2` — the Nyquist of the *angle* axis.
Measured: a pure order-3.5 component on a 600 -> 1800 rpm ramp, resampled at
64 samples/rev over 78 whole revolutions, reads amplitude 0.999371 in a
single bin of the order spectrum; the same component in the ordinary
spectrum peaks at 0.070203 and is 66.5 Hz wide.
Raises `ValueError: everything :func:_as_signal` refuses, a
non-positive or wrong-length `rpm, samples_per_rev` outside
`[2, 65536], an output over :data:MAX_ANGULAR_SAMPLES`, fewer than one
complete revolution in the record, and — the aliasing refusal — a
`samples_per_rev` whose implied Nyquist order needs content above the
time-domain Nyquist. Asking for 64 samples/rev on a shaft turning at 30 Hz
means representing 960 Hz, which a 100 Hz recording does not contain; the
resampler would happily manufacture it from the interpolation.
• acoustic_condition_monitoring family guide
• Sample-data catalog (download URLs / licences) — 2-D uses skimage.data (BSD/public domain) plus synthetic images; 3-D lists download URLs for real data sources (Stanford, PDS, …).
• Operator provenance and references — the sources of the research/methods this op family came from.
• The canonical algorithm (author, year) and its uses are named in the family usage guide above.
• acoustic_condition_monitoring — py -3.11 examples/acoustic_condition_monitoring.py
table as input)order)*Provenance: acoustics.py — ACOUSTICS operator registry. This per-op note is generated by tools/opdocs.py md (do not hand-edit).*
© 2026 Kazufumi Furuse — Fullseye operator documentation. Licensed under Apache-2.0.