Source: https://jmrplens.github.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://jmrplens.github.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://jmrplens.github.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 Two vocabulary edges: **class 0** belongs to the withdrawn IEC 61260:1995 / ANSI S1.11-2004 masks, not to the 2014 edition (see [Filter class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://jmrplens.github.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` | IEC 61260-1:2014 Table 1 (1995 mask via `edition="1995"`) | | 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 for a decimated bank ``` Read the flags, not just the class: `range_limited` is `True` on the decimated bank because a band cannot be evaluated beyond its own processing Nyquist, so the far stopband rests on the anti-alias argument rather than on the band filter itself. The details, including why a +0.400 dB margin is the ceiling for a passing Butterworth bank, are in [Filter class verification](https://jmrplens.github.io/phonometry/signals/filters/filter-compliance/); the weighting side is section 6 of [Frequency weighting](https://jmrplens.github.io/phonometry/signals/levels/weighting/). When the verdict has to leave the console, `filter_class_compliance` wraps the same verification as a result object with `.plot()` and `.report()`, the one-page accredited fiche with an optional PASS/FAIL row against a required class; `intensity_class_compliance` does the same for the IEC 61043 residual-index verdict: ```python from phonometry import OctaveFilterBank, ReportMetadata, filter_class_compliance bank_11 = OctaveFilterBank(fs=48000, fraction=1, order=6, limits=[125, 4000]) result = filter_class_compliance(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 ``` ## Reading the conformance report The verifiers grade *your* configuration; the [conformance report](https://jmrplens.github.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://jmrplens.github.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. **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 verifier verdict 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. It is *not* 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 conformance per IEC 60942, both discussed in [Calibration and dBFS](https://jmrplens.github.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*) and IEC 61672-3:2013 (*Periodic tests*): the instrument test regimes delimited above, not run. IEC 61260-1:2014, *Octave-band and fractional-octave-band filters — Part 1: Specifications*: the Table 1 acceptance limits checked by `verify_filter_class`. IEC 61260-2:2016 (*Pattern-evaluation tests*) and IEC 61260-3:2016 (*Periodic tests*): the filter-set test regimes delimited above, not run. IEC 61043:1993, *Instruments for the measurement of sound intensity*: the class limits behind `verify_intensity_class`. **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.