order op• Data kinds: signal → table
• Call: import fullseye as fs; fs.ledger.order_spectrum(x, rate, rpm, samples_per_rev=64, revolutions=None, max_order=None, n_peaks=5) (to call the implementation directly, import acoustics; acoustics.order_spectrum(x, rate, rpm, samples_per_rev=64, revolutions=None, max_order=None, n_peaks=5); from the registry, opsacoustics.get("order_spectrum"))
Amplitude against shaft order — the spectrum a run-up should be read in.
angular_resample followed by an rFFT over a whole number of revolutions (the record is cropped to that). Bin spacing is 1 / whole_revolutions in orders.
revolutions overrides how many whole revolutions to keep, and it matters more than it looks. An order o lands exactly on a bin only when o * revolutions is an integer; otherwise it straddles two and both read low. Measured on the run-up below, which happens to cover 79.994
revolutions:
============== ========== ============= =============
revolutions resolution amp at o=1.0 amp at o=3.5
============== ========== ============= =============
79 (default) 0.012658 0.999967 0.636961
78 (even) 0.012821 1.000009 0.999371
============== ========== ============= =============
That 0.637 is the classic two-bin scallop loss, and nothing raises: the peak is at the right order and 36 % too small, with a second peak of almost equal height one bin away (measured 0.6370 at order 3.4937 and 0.6353 at 3.5063). Cropping to an even number of revolutions puts every half-integer order on a bin. The default is the largest whole number available; pass revolutions when the order you care about is fractional.
Returns a dict: orders, magnitude (single-sided, 2/N), peak_order, peak_amplitude, peak_orders / peak_amplitudes, resolution_order, whole_revolutions, samples_per_rev, mean_rpm, max_order.
Measured, and this is the whole argument for the operator. A 4 s run-up from 600 to 1800 rpm at 5 kHz carrying exactly two shaft-locked components (orders 1.0 and 3.5, unit amplitude) plus one fixed 400 Hz resonance, read with revolutions=78:
========================== ===================== ====================
quantity ordinary spectrum order spectrum
========================== ===================== ====================
order-3.5 peak amplitude 0.070203 (of true 1) 0.999371 (of true 1)
its -3 dB width 66.50 Hz (= 3.33 ord) 0.00000 order
400 Hz resonance amplitude 1.0000, one bin 0.0517, over 26.7 ord
========================== ===================== ====================
The ordinary spectrum recovers 7 % of the shaft-locked component's amplitude, because the energy is spread over 3.3 orders' worth of bins; the order spectrum recovers 99.94 % of it in a single bin whose -3 dB width is one bin. The 400 Hz resonance goes the other way — sharp in hertz, smeared across 26.7 orders after resampling. That reversal is the diagnostic, and it is why both spectra are worth computing: what stays sharp under angular resampling turns with the shaft, and what stays sharp under ordinary transformation does not.
Raises ValueError: everything angular_resample refuses (in particular the aliasing refusal), a revolutions larger than the record actually contains, and a max_order above the angular Nyquist samples_per_rev/2.
• 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.