Source: https://docs.jmrp.io/phonometry/signals/metrology/compliance-verification/ # Compliance and verification Three kinds of evidence back a number computed with this library. The **verifiers** are public functions that grade a filter or weighting you configured against the acceptance limits of its governing standard. The **conformance report** ([docs/CONFORMANCE.md](https://docs.jmrp.io/phonometry/reference/conformance/)) pins the shipped implementation to the standards' own expected values and is regenerated on every change. And the **scope notes** on each guide say where the software's claim ends and a laboratory's begins. This page is the map of the three. ## What a performance class asserts IEC 61672-1:2013 (sound level meters) and IEC 61260-1:2014 (fractional-octave filters) both specify two performance categories, **class 1 and class 2**, and both define them the same way: the two classes share the *same design goals* and differ mainly in the **acceptance limits** around those goals and in the range of operational temperature; class 2 limits are greater than or equal to class 1 limits everywhere (IEC 61672-1:2013 clause 1; IEC 61260-1:2014 subclause 1.2). A class is therefore not a quality grade but a **worst-case error bound under stated conditions**, and the bound chains: a class 1 measurement needs every stage at class 1, from the [calibrator](https://docs.jmrp.io/phonometry/signals/metrology/calibration/) through the weighting to the band filter. One class 2 stage bounds the chain at class 2. Two vocabulary edges: **class 0** belongs to the withdrawn IEC 61260:1995 / ANSI S1.11-2004 masks, not to the 2014 edition (see [Filter class verification](https://docs.jmrp.io/phonometry/signals/filters/filter-compliance/)); and a class belongs to a specification, so the honest claim is "class 1 per IEC 61672-1:2013 Table 3" or "class 1 per IEC 61260-1:2014 Table 1", never "class 1" alone. ## The verifiers: which function proves what One verifier per instrument stage, all sharing the same verdict vocabulary: `overall_class` (the strictest class met, or `None`), per-band margins in decibels to the nearest limit, and a `range_limited` flag when part of the standard's frequency range could not be demonstrated at your sample rate. | Stage | Verifier | Acceptance limits | | :--- | :--- | :--- | | Frequency weighting (A, C, Z) | `verify_weighting_class` | IEC 61672-1:2013 Table 3 | | Weightings B and AU | `verify_weighting_class` | ANSI S1.4-1983 Tables IV/V; IEC 61012:1990 Table 1 | | Fractional-octave filter bank | `verify_filter_class`; `verify_time_invariance` | IEC 61260-1:2014 Table 1, 5.12 and 5.16 as IEC 61260-2 computes them (1995 mask via `edition="1995"`); 5.14 by an exponential sweep | | Intensity instrument spectrum | `verify_intensity_class` | IEC 61043:1993 Table 2 | The masks are public too: `weighting_class_limits(1)` returns the Table 3 corridor and `class_limits(fraction, filter_class, omega)` the Table 1 one, so a report can draw the limits a verdict was judged against. Verifying a whole chain, in the configuration the conformance suite itself pins (48 kHz, order 6, one-third-octave, 100 Hz to 10 kHz): ```python from phonometry import filters wf = filters.WeightingFilter(48000, "A") weighting = filters.verify_weighting_class(wf) print(weighting.overall_class) # 1 print(weighting.range_limited) # False bank = filters.OctaveFilterBank(fs=48000, fraction=3, order=6, limits=[100, 10000]) bands = filters.verify_filter_class(bank) print(bands.overall_class) # 1 print(bands.range_limited) # True: its top bands reach Nyquist ``` Read the flags, not just the class: `range_limited` is `True` on this bank because its bands from 5 kHz up, filtered at the full rate, cannot be evaluated beyond the 24 kHz Nyquist frequency, which falls short of the end of their Table 1 mask, so their far stopband rests on the anti-alias filter of the capture chain rather than on the band filter itself. The class is the strictest met on every requirement graded (`bands.requirements`), and a bank can still part company with its Table 1 verdict: at 48 kHz an order-4 one-third-octave bank is class 1 on Table 1 and misses class 1 on the summation of 5.16 by 0.002 dB, at its 16 kHz band. The details, including why a +0.400 dB margin is the ceiling for a passing Butterworth bank, are in [Filter class verification](https://docs.jmrp.io/phonometry/signals/filters/filter-compliance/); the weighting side is section 6 of [Frequency weighting](https://docs.jmrp.io/phonometry/signals/levels/weighting/). A and C weighting deviations at 48 kHz threading within the IEC 61672-1 Table 3 class 1 acceptance corridor, with the wider class 2 limits dotted When the verdict has to leave the console, the same call answers: what `verify_filter_class` returns carries `.plot()` and `.report()`, the one-page accredited fiche with an optional PASS/FAIL row against a required class, and `verify_intensity_class` does the same for the IEC 61043 residual-index verdict: ```python from phonometry import ReportMetadata, filters bank_11 = filters.OctaveFilterBank(fs=48000, fraction=1, order=6, limits=[125, 4000]) result = filters.verify_filter_class(bank_11) # result.overall_class == 1 result.report( "iec61260.pdf", metadata=ReportMetadata( specimen="1/1-octave filter bank", measurement_standard="IEC 61260-1:2014", required_class=1, ), ) # -> Class 1 - COMPLIES, PASS ``` **The verifiers that grade a measurement, not a design.** Eight more functions carry the same `verify_` prefix and answer a different question. The four above are handed a filter this library built, and report whether that *design* fits an acceptance mask; these are handed numbers somebody measured on a bench, and report whether *that instrument, on the day it was measured*, meets the standard it is sold against. There are no classes and no decibel margins in them: the verdict is a pass or a fail, in the unit its own standard writes its tolerances in. All eight return a result object whose verdict says so and whose other fields say where and by how much, down to `verify_running_rms_decay`, which grades one printed row and keeps it. | What is graded | Verifier | Acceptance limits | | :--- | :--- | :--- | | Aircraft-noise measurement system | `verify_aircraft_noise_system` | IEC 61265:1995 Table 1, and the scalar limits beside it | | Human-vibration frequency weighting | `verify_weighting` | ISO 8041-1:2017 Tables 4 and 5 | | Human-vibration phase response | `verify_phase_response` | ISO 8041-1:2017 Table 5 and Formula (6) | | Saw-tooth burst indications | `verify_signal_burst_response` | ISO 8041-1:2017 Tables 7 to 9 (the signal is Table 6) | | Running r.m.s. decay time | `verify_running_rms_decay` | ISO 8041-1:2017 Tables 10 and 11 | | Sound calibrator | `verify_sound_calibrator` | IEC 60942:2017 Tables 2 to 7 and A.1 to A.5 | | Sound level meter periodic test | `verify_sound_level_meter_periodic` | IEC 61672-3:2013 clauses 12 to 21, with the limits of IEC 61672-1:2013 (Tables 3 to 5 and its text) and the maxima of its Table B.1 | | Band-filter periodic test | `verify_filter_periodic` | IEC 61260-3:2016 clauses 10, 11 and 13 and Table 1, with the maxima of IEC 61260-1:2014 Annex B | One clause of ISO 8041-1 makes those four different in kind from everything else on this page. The deviation a laboratory reports is extended by that laboratory's own expanded uncertainty before it is compared with the limit (clauses 13.1 and 14.1), so the same instrument passes on one bench and fails on another, and `verify_weighting` takes that uncertainty as an argument rather than assuming it away. The four are covered by [Verifying a human-vibration meter](https://docs.jmrp.io/phonometry/vibration/human/meter-verification/), and the aircraft one by [Aircraft noise](https://docs.jmrp.io/phonometry/aircraft/aircraft-noise/). **The conformance rule of IEC TC 29.** The IEC instrument standards written since 2013 answer the same question another way, in the same sentence: IEC 61672-1:2013 5.1.21, IEC 60942:2017 5.1.15, IEC 61672-3:2013 4.1 and the introductions of IEC 61260-2 and -3:2016. Conformance is demonstrated when the measured deviation does not exceed the acceptance limits **and** the laboratory's actual expanded uncertainty does not exceed the maximum-permitted uncertainty the standard prints for the test, both limits inclusive. The uncertainty is not added to the deviation: the tolerance the instrument has to meet lies beyond the acceptance limit by that maximum (IEC 60942 Annex D, IEC 61672-1 Annex A), a guard band stated for a 95 % coverage interval that lowers the risk of passing an instrument outside its tolerance without removing it. `metrology.verify_conformance` is the rule on its own, and its verdict names which of the four outcomes of IEC 60942 E.2.2 it is, in the words of the tables' "Reasons" column. One end of the acceptance interval may be open, `acceptance_limits=(70.0, math.inf)`, for a stop-band requirement that has a minimum and no maximum. `verify_sound_calibrator` applies the rule to every requirement of IEC 60942:2017 (see [Calibration and dBFS](https://docs.jmrp.io/phonometry/signals/metrology/calibration/)), `verify_sound_level_meter_periodic` to every result of an IEC 61672-3:2013 periodic test (see [Periodic tests of a sound level meter](https://docs.jmrp.io/phonometry/signals/metrology/sound-level-meter-periodic-tests/)), and `verify_filter_periodic` to every result of an IEC 61260-3:2016 periodic test (see [Filter class verification](https://docs.jmrp.io/phonometry/signals/filters/filter-compliance/)). ```python from phonometry import metrology # IEC 61672-1:2013 Table C.1: acceptance limits +1.0 dB and -1.2 dB, and a # maximum-permitted uncertainty of 0.5 dB. on_the_limit = metrology.verify_conformance( # example 7 -1.2, uncertainty=0.3, acceptance_limits=(-1.2, 1.0), max_uncertainty=0.5) print(on_the_limit.passes, on_the_limit.outcome) # True 1 both_out = metrology.verify_conformance( # example 10 -2.0, uncertainty=0.7, acceptance_limits=(-1.2, 1.0), max_uncertainty=0.5) print(both_out.passes, both_out.outcome) # False 4 ``` The eight examples of IEC 60942:2017 Table E.1 between 0 dB and 0.25 dB, as Figure E.1 draws their absolute deviations, and the ten of IEC 61672-1:2013 Table C.1 between -1.2 dB and +1.0 dB, each marker the verdict verify_conformance returned, which is the verdict the table prints All eighteen examples are rows of the [conformance report](https://docs.jmrp.io/phonometry/reference/conformance/), verdict and printed reason each, and so are the same ten as IEC 61260-1:2014 Table C.1 prints them. ## Reading the conformance report The verifiers grade *your* configuration; the [conformance report](https://docs.jmrp.io/phonometry/reference/conformance/) is the complementary evidence for the implementation as shipped: each row pins one implemented quantity to the governing standard's own expected value (a worked example or a tolerance-table entry, not a regression baseline), with the computed value, the signed delta and a pass/fail verdict. It is regenerated on every pull request and CI fails if it drifts from the code. Use it in three ways: find the row for a metric before trusting it (the row names the standard, edition and clause the implementation was held to); note that the class rows walk one pinned configuration, so section 2's verifiers are how the claim transfers to your own bank; and cite the report of the exact library version you pinned. Defects the re-derivation exposed in the published standards themselves are in the [errata registry](https://docs.jmrp.io/phonometry/reference/errata/). ## What only a laboratory can attest Both instrument series continue past their Part 1 with two test regimes, and neither is something a software library can run on itself. What the library can do with them is arithmetic: the requirements of a filter set that Part 2 computes from a response are computed on the design, and the results a Part 3 test of a meter or of a filter set returns are graded by `verify_sound_level_meter_periodic` and `verify_filter_periodic`, which run none of the tests. Three stacked bands, one for each part of the two instrument series, with sound level meters to IEC 61672 on the left and band filters to IEC 61260 on the right. A box at the top stands for the transfer function configured in phonometry, and two arrows, one labelled verify_weighting_class and one labelled verify_filter_class and verify_time_invariance, reach down into the first band only. Part 1 holds the specifications: Table 3 of IEC 61672-1, the A, C and Z weightings at 34 frequencies from 10 Hz to 20 kHz with ±0.7 dB at 1 kHz for class 1, and Table 1 of IEC 61260-1, a relative attenuation corridor with ±0.4 dB at the mid-band, with the effective bandwidth, the sweep and the summation of 5.12, 5.14 and 5.16, each with the largest uncertainty a laboratory may claim it with. A dashed line separates a design checked in software from a physical instrument in a laboratory. Part 2, pattern evaluation, shows at least three specimens submitted, at least two selected and at least one tested in full, with the environmental, electrostatic, radio-frequency, free-field, linearity and climate tests, and a report that states whether the pattern is approved. An arrow carries that approval down to Part 3, periodic tests on one working instrument at 20 °C to 26 °C with a limited set of checks, which support no general conclusion without it; two more arrows run from the phonometry box down the outer margins, verify_sound_level_meter_periodic on the left into the IEC 61672-3 cell and verify_filter_periodic on the right into the IEC 61260-3 cell, the grading of a laboratory's periodic results. A box at the foot gives the conformance criterion: the deviation within the acceptance limits and the uncertainty no larger than its maximum, of which a design verifier reads the first half and the two periodic graders grade both. *The two series side by side, their three parts stacked. The design verifiers reach only the Part 1 requirements and only the first half of the conformance criterion; Parts 2 and 3, under the dashed line, need a physical instrument, whose periodic-test results `verify_sound_level_meter_periodic` and `verify_filter_periodic` grade on both halves, and a periodic test says nothing general until the pattern approval it leans on is public.* **Pattern evaluation** (IEC 61672-2:2013 for meters, IEC 61260-2:2016 for filters) is the type-approval regime a *model* passes once: the tests necessary to verify conformance to **all mandatory specifications** of the Part 1 (IEC 61672-2:2013 clause 1; IEC 61260-2:2016 subclause 1.1), on physical specimens (IEC 61260-2 requires at least three of them (subclause 4.1)). That includes everything a transfer function does not have: static pressure, air temperature and humidity influence, electrostatic and radio-frequency immunity, directional response, acoustical tests of the weightings with the microphone in the sound field, level linearity of real electronics, self-generated noise, tonebursts and overload behaviour (IEC 61672-2:2013 clauses 7 to 9; IEC 61260-2:2016 clauses 7 to 9). **Periodic tests** (IEC 61672-3:2013, IEC 61260-3:2016) are what a *working instrument* receives in the laboratory, typically every year or two, on a limited set of key tests "restricted to the minimum considered necessary", valid for the environmental conditions of the day (IEC 61672-3:2013 clause 1; IEC 61260-3:2016 subclauses 1.2 and 1.3). Both Part 3 scopes end with the same caveat: passing every periodic test supports **no general conclusion of conformance** to the Part 1 unless the model's pattern approval is on record (IEC 61672-3:2013 clause 1; IEC 61260-3:2016 subclause 1.5). The same honesty applies to this library, in both directions. A verdict from one of the four class verifiers is a statement about a *design*: the digital transfer function you configured fits the Part 1 acceptance mask, with the reported margins, over the checked range; every measurement made wholly in software inherits it. A verdict from one of the eight that grade a measurement is narrower still: it belongs to the numbers somebody put in, on the day they were measured, and nothing else inherits it. Neither is a pattern evaluation, a periodic test, or a certificate for any physical device: nothing here has a microphone, a temperature or a serial number, and a real front end brings its own paper: the meter's periodic test per IEC 61672-3 and the calibrator's laboratory results per IEC 60942, which `verify_sound_level_meter_periodic` and `verify_sound_calibrator` grade but cannot produce (as `verify_filter_periodic` grades a filter set's IEC 61260-3 results), discussed in [Periodic tests of a sound level meter](https://docs.jmrp.io/phonometry/signals/metrology/sound-level-meter-periodic-tests/) and [Calibration and dBFS](https://docs.jmrp.io/phonometry/signals/metrology/calibration/). A defensible report names both verdicts: the library's design verdict with the version and its conformance report, and the instrument's test record with its date. ## Standards IEC 61672-1:2013, *Sound level meters — Part 1: Specifications*: the two performance categories and the Table 3 acceptance limits checked by `verify_weighting_class`. IEC 61672-2:2013 (*Pattern evaluation tests*): the type-approval regime delimited above, not run. IEC 61672-3:2013 (*Periodic tests*): the tests are delimited above, not run; `verify_sound_level_meter_periodic` grades the results a laboratory returns, with Tables 4, 5 and B.1 of IEC 61672-1:2013, which it publishes. IEC 61260-1:2014, *Octave-band and fractional-octave-band filters — Part 1: Specifications*: the Table 1 acceptance limits, the effective bandwidth of 5.12 and the summation of 5.16 checked by `verify_filter_class`, the time-invariant operation of 5.14 by `verify_time_invariance`, and the Annex B maxima of the periodic tests. IEC 61260-2:2016 (*Pattern-evaluation tests*): Formulas (1) to (3) and the swept test of 7.4, computed on a design; the tests on a specimen are delimited above, not run. IEC 61260-3:2016 (*Periodic tests*): the tests are delimited above, not run; `verify_filter_periodic` grades the results a laboratory returns. IEC 61043:1993, *Instruments for the measurement of sound intensity*: the class limits behind `verify_intensity_class`. IEC 60942:2017, *Sound calibrators*: the conformance rule of 5.1.15 and Annex D, the eight examples of Table E.1 that `verify_conformance` reproduces, and the requirements `verify_sound_calibrator` grades. IEC 61672-1:2013 5.1.21 and Table C.1 give the same rule and ten more examples. **Not covered.** The verification mathematics of each stage belongs to that stage's own page; and every test of the Parts 2 and 3 themselves is delimited here but not performed: no environmental, immunity, acoustical or linearity test is run, and no physical instrument is assigned a class. `verify_sound_level_meter_periodic` and `verify_filter_periodic` grade the results of a meter's and a filter set's periodic tests; they do not produce them.