hearing.active_noise_reduction

Total attenuation of an active noise reduction earmuff (ISO 4869-6:2019).

An active noise reduction (ANR) earmuff adds a cancellation circuit to a passive one, and the circuit works mostly at low frequencies, where the passive shell is weakest. ISO 4869-1 cannot measure it: a threshold test runs at levels far below those at which the circuit has anything to cancel. So ISO 4869-6 measures the two halves separately and adds them subject by subject:

• the passive attenuation, the real-ear attenuation at threshold of ISO 4869-1 with the circuit off, in octave bands (real_ear_attenuation);

• the active insertion loss (3.4), measured with a microphone in each closed ear canal (MIRE, ISO 11904-1) as the difference between the level at the ear in the passive and in the active mode, in one-third-octave bands of a broadband noise at 85 dB to 95 dB (5.4.3):

  $${\alpha }_{j,e,f}=L_{\mathrm{passive},j,e,f}-L_{\mathrm{active},j,e,f}$$

The chain of 5.5. For each subject:

a) the passive attenuation is interpolated linearly into the one-third-octave bands between 63 Hz (or 125 Hz) and 8 kHz, and extrapolated to 50 Hz (or 100 Hz) and 10 kHz; b) in each one-third-octave band, only the ear with the lower active insertion loss is kept; c) the two are added, $A_{\mathrm{total},f,j}$; d) each octave band is the energetic average of its three one-third-octave bands (Formula (1)):

e) the sixteen octave-band data sets go into ISO 4869-2 at a protection performance of 84 %: the mean, the standard deviation, the APV, the H, M and L values and the SNR.

anr_total_attenuation runs the whole chain. Clause 5.5 says the detailed computations are given in the calculation example ISO publishes with the standard, and that workbook interpolates linearly in frequency, in hertz, between the nominal centre frequencies, not on a logarithmic axis: 80 Hz sits 27 % of the way from 63 Hz to 125 Hz, not a third of it. This follows the workbook. The workbook also rounds each interpolated value and each octave result to 0,1 dB, and the mean and standard deviation before it forms the APV; this computes at full precision throughout, which moves an octave-band total by less than 0,1 dB.

The uncertainty (Annex A). Formula (A.1) is the model of ISO 4869-1 applied to the active insertion loss, and within one laboratory the combined standard uncertainty is again the standard deviation of the mean over the sixteen lower-ear values, $u=s/\sqrt{N}$ and $U_{95}=2u$, which active_insertion_loss returns. Table A.2 prints a typical budget, ANR_WITHIN_LABORATORY_UNCERTAINTY.

Linear operation (5.4.4). A cancellation circuit saturates, so the active insertion loss only holds up to some external level. With red noise, the level at each ear in the 125 Hz octave band is followed while the external level rises in 5 dB steps from the level of the insertion-loss measurement to at most 110 dB, and each step at the ear shall also be 5 dB, within ±1 dB. assess_anr_linearity finds the highest external level up to which that holds for every sample, subject and ear, which is what 5.6 i) reports.

Clause, formula and table numbers refer to ISO 4869-6:2019(E).

Auto-generated from the source docstrings by scripts/generate_api_docs.py (make api-docs). Do not edit by hand.

active_insertion_loss(
    insertion_loss_db: ArrayLike | None = None,
    *,
    passive_levels_db: ArrayLike | None = None,
    active_levels_db: ArrayLike | None = None,
    frequencies: ArrayLike | None = None,
) -> ActiveInsertionLossResult

The active insertion loss, its lower ear and its uncertainty (5.4, 5.5 b), A.2).

Give the levels at the ears in the two modes, both (subjects, 2, bands) grids with the left ear first, and the insertion loss of each ear is their difference (5.4.1):

or give the insertion loss directly, per ear on the same grid or already reduced to one value per subject and band. Per subject and band only the ear with the lower value is kept (5.5 b)), and over those the mean, the standard deviation and the uncertainty of the mean of Annex A are formed:

A negative value is a band in which the circuit adds sound, which ANR earmuffs commonly do above 1 kHz; it is kept as it is.

Parameters

Returns: ActiveInsertionLossResult.

Raises

ActiveInsertionLossResult(
    insertion_loss_db: np.ndarray,
    per_ear_db: np.ndarray | None,
    mean_db: np.ndarray,
    standard_deviation_db: np.ndarray,
    standard_uncertainty_db: np.ndarray,
    expanded_uncertainty_db: np.ndarray,
    frequencies: np.ndarray,
    subjects: int,
)

The active insertion loss of an ANR earmuff on a panel of subjects.

Attributes

ActiveInsertionLossResult.plot(
    ax: Axes | None = None,
    *,
    language: str = 'en',
    **kwargs: Any,
) -> Axes

Draw the mean active insertion loss with its expanded uncertainty.

Parameters

Returns: The axes.

anr_total_attenuation(
    reat: ArrayLike | RealEarAttenuationResult,
    insertion_loss: ArrayLike | ActiveInsertionLossResult,
) -> AnrTotalAttenuationResult

The total attenuation of an ANR earmuff, subject by subject (5.5).

Runs 5.5 a) to e): the passive attenuation of ISO 4869-1 is interpolated into one-third-octave bands, linearly in hertz and extended at both ends; the lower-ear active insertion loss is added to it; each octave band is the energetic average of its three one-third-octave bands,

and the octave-band totals of all subjects go into ISO 4869-2 at 84 %. The same subjects are measured passively and actively (5.4.3), so the two inputs must have the same subjects, in the same order.

The passive attenuation from 63 Hz needs the active insertion loss from 50 Hz; from 125 Hz, it needs it from 100 Hz. An insertion loss that starts at 100 Hz can only give the total from 125 Hz (5.3.1); a passive attenuation from 63 Hz then still places the 100 Hz band, by interpolation.

Parameters

Returns: AnrTotalAttenuationResult.

Raises

Constant (phonometry.hearing.real_ear_attenuation.ProtectorUncertaintyBudget).

AnrLinearityResult(
    external_levels_db: np.ndarray,
    ear_levels_db: np.ndarray,
    increments_db: np.ndarray,
)

How far up an ANR earmuff stays linear (5.4.4).

Attributes

property

Per ear and step, whether the step at the ear is 5 dB ± 1 dB.

Returns: A (ears, steps) boolean grid.

property

Whether it stayed linear up to 110 dB, which 5.6 i) then states.

Returns: True when every step is linear and the last external level is 110 dB.

property

The highest external level up to which every ear stayed linear, in dB.

Read from linear, the same judgement passes makes: the level before the first step at which any ear leaves 5 dB ± 1 dB, or the last level applied when none does. The lowest level applied when the first step already fails.

Returns: The level 5.6 i) reports, in dB.

property

Whether every step at every ear stayed linear.

Returns: True when the earmuff is linear over the whole range tested.

AnrLinearityResult.plot(
    ax: Axes | None = None,
    *,
    language: str = 'en',
    **kwargs: Any,
) -> Axes

Draw every step at the ear against the 5 dB ± 1 dB it should be.

Parameters

Returns: The axes.

AnrTotalAttenuationResult(
    total_octave_db: np.ndarray,
    total_third_octave_db: np.ndarray,
    reat_third_octave_db: np.ndarray,
    insertion_loss_db: np.ndarray,
    frequencies: np.ndarray,
    third_octave_frequencies: np.ndarray,
    assumed_protection: AssumedProtectionResult,
    hml: HMLRatingResult,
    snr: SNRRatingResult,
)

The total attenuation of an ANR earmuff and its ISO 4869-2 ratings (5.5).

Attributes

AnrTotalAttenuationResult.plot(
    ax: Axes | None = None,
    *,
    language: str = 'en',
    **kwargs: Any,
) -> Axes

Draw the passive, active and total attenuation and the APV.

Parameters

Returns: The axes.

assess_anr_linearity(
    external_levels_db: ArrayLike,
    ear_levels_db: ArrayLike | None = None,
    *,
    ear_third_octave_levels_db: ArrayLike | None = None,
) -> AnrLinearityResult

Up to what external level does the earmuff stay linear? (5.4.4).

With red noise (5.3.2) and the circuit on, the external A-weighted level starts at the level of the insertion-loss measurement and rises in 5 dB steps to at most 110 dB. At each ear the level in the 125 Hz octave band, the energy sum of the 100 Hz, 125 Hz and 160 Hz one-third-octave bands, shall rise by the same 5 dB, within ±1 dB. The highest external level up to which that holds for every sample and subject is what 5.6 i) reports, and if it holds up to 110 dB, that is stated.

Parameters

Returns: AnrLinearityResult.

Raises