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phonometry

website·Indexed 30 days ago

https://jmrplens.github.io/phonometry/

A Python-based framework for acoustic measurement, analysis, and prediction. It provides tools for signal analysis (octave filtering, weighting, calibration), aircraft noise certification (ICAO Annex 16, IEC 61265, ECAC Doc 29/32), and building acoustics including sound insulation and prediction according to ISO 10140, ISO 16283, ISO 717, and EN 12354 standards.

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What's inside phonometry

  1. Overview of aircraft noise computation methods

    Aircraft noise is computed using two primary internationally negotiated methods:

    1. Certification: Establishes a single noise value per aircraft type at standard reference points around a runway. The primary metric is Effective Perceived Noise Level (EPNL) per ICAO Annex 16, which converts a one-third-octave time history into an EPNdB value using perceived noisiness, tone correction, and duration correction.
    2. Contour Methods: Predicts the noise impact of a fleet on the surrounding ground area.
      • For fixed-wing aircraft, ECAC Doc 29 uses noise-power-distance (NPD) tables and flight path corrections (impedance, lateral attenuation, engine installation, etc.) to create single-event contours.
      • For rotorcraft (helicopters), ECAC Doc 32 uses a noise hemisphere model (band levels on a grid of emission angles at a 60m reference distance) combined with spherical spreading, atmospheric absorption, and the Chien-Soroka ground effect to calculate SEL, LASmax, and EPNL contours.

  2. Overview of the Sound Assessment and Regulation Chain

    Sound assessment is treated as a three-link chain used to determine if a sound level meets national regulatory limits. The process follows this sequence:

    1. Indicator: Averages the sound over a defined period (e.g., using ISO 1996).
    2. Adjustments: Adds decibels to the average to account for sound character, such as tone or impulses (e.g., tonal adjustments from ISO 1996-2 or impulsive adjustments from NT ACOU 112).
    3. Limit: A national regulatory value used to decide if the adjusted level is acceptable.

  3. Overview of Vibration and Structure-Borne Sound Applications

    Vibration is analyzed in acoustics through three primary lenses:

    1. Source of Sound: Structure-borne power (e.g., from pumps or fans) travels through building elements and re-radiates as audible noise.
    2. Human Exposure: Vibration transmitted to people (standing, seated, or hand-gripping) is measured and limited using specific metrics and legal action values.
    3. Machine Diagnosis: Vibration spectra are used to identify faults in bearings, gears, or blades based on the periodicity fixed by the machine's geometry.

  4. Overview of Phonometry signal and spectral analysis tools

    The Phonometry library provides a suite of calibrated signal analysis tools based on Bendat & Piersol. Every estimate is calibrated using the same dB SPL / dBFS reference frames as the rest of the library and includes statistical quality (e.g., confidence intervals).

    Key analysis families include:

    • Frequency-domain estimators: Spectral analysis (Welch PSD, cross-spectral density), multiple and partial coherence, and colored-noise generators (white, pink, red, blue, violet).
    • Time-frequency analysis: Calibrated STFT spectrograms and zoom FFT for narrow-band analysis.
    • Spectrum-shape methods: Power, real, and complex cepstrum for echo detection and liftering; envelope spectrum for amplitude modulation.
    • Period-domain methods: Time synchronous averaging to extract repetitive waveforms from noise.
    • Time-domain estimators: Auto- and cross-correlation, time-delay estimation (GCC-PHAT, Roth, SCOT, ML), and Hilbert transforms for envelopes.
    • Stimulus and System Toolbox: IEC 60268-1 tone bursts, polyphase resampling, Golay pairs for system deconvolving, and Mueller & Massarani shaped sweeps.

  5. Overview of Psychoacoustic Metrics and Reference Anchors

    Psychoacoustics quantifies what a listener perceives rather than physical decibel levels. These metrics are level-dependent and require an absolutely calibrated signal in pascals. Each metric is defined by a specific reference sound anchor:

    • Loudness (Sones): 1 sone = 1 kHz tone at 40 dB SPL.
    • Sharpness (Acums): 1 acum = critical-band-wide noise at 1 kHz and 60 dB.
    • Roughness (Asper): 1 asper = 1 kHz carrier fully modulated at 70 Hz at 60 dB.
    • Fluctuation Strength (Vacil): 1 vacil = 1 kHz carrier modulated at 4 Hz at 60 dB.
    • Tonality (tu_HMS): 1 tu_HMS = 1 kHz tone at 40 dB.

  6. Overview of ISO 15186 Sound Insulation Standards

    The phonometry library implements sound insulation measurements based on the ISO 15186 series. Key standards include:

    • ISO 15186-1:2000: Laboratory measurements defining the intensity sound reduction index $R_I$, the $K_c$-modified form $R_{I,M}$ (Annex B), the element normalized level difference $D_{I,n,e}$, and the surface pressure-intensity indicator.
    • ISO 15186-2:2003: Field measurements, applying the same quantities to determine the apparent index $R'_I$ of installed elements.
    • ISO 15186-3:2002: Low-frequency laboratory measurements (down to 50 Hz). This variant reads the source level on the specimen surface and subtracts 9 dB instead of 6 dB, utilizing a limp-panel qualification (Annex A).

  7. Overview of ISO 717 Sound Insulation Rating Implementations

    The library provides implementations for calculating single-number insulation ratings based on ISO 717-1:2020 (airborne sound) and ISO 717-2:2020 (impact sound). This includes the calculation of reference-curve ratings, spectrum adaptation terms ($C$, $C_{\mathrm{tr}}$, and $C_{\mathrm{I}}$), enlarged-range terms from Annex B / A.2.1, and 0.1 dB-step variants for uncertainty statements. These engines process band spectra derived from various standards, including ISO 16283 (field), ISO 10140 (laboratory), ISO 15186 (intensity), ISO 10052 (survey), and ISO 10848 (flanking).

  8. Overview of phonometry design philosophy

    phonometry is a standards-based acoustic measurement toolkit. Its core differentiator is that every metric is implemented directly from the governing standard's text. Reference values and acceptance limits from these standards are transcribed into the test suite and enforced via Continuous Integration (CI) to ensure strict conformance.

  9. Overview of Electroacoustics measurement tools

    The Electroacoustics suite provides tools for the characterization and reporting of audio devices based on international standards. It is divided into three primary device categories:

    1. Amplifiers: Focuses on distortion metrics (THD, THD+N, SINAD, intermodulation, and DIM) following IEC 60268-3. Measurements are taken based on rated load impedance, supply, and source impedance.
    2. Loudspeakers: Follows IEC 60268-5 for characterization, including sensitivity conventions, radiating-piston models for directivity, and the generation of a characteristics fiche. It also includes tools for sound-reinforcement system diagnosis, such as Long's gain-before-feedback criterion and correction for the number of open microphones.
    3. Microphones: Follows IEC 60268-4 for characterization, covering sensitivity references, polar patterns, and inherent-noise conventions to produce a standard laboratory report.

    Additionally, the suite includes utilities for swept-sine distortion (Farina/Novak harmonic separation) to derive THD as a function of frequency, as well as phase analysis tools (minimum-phase, group-delay, and excess-phase).

  10. Overview of 2D FDTD wave simulation

    The fdtd_simulation module integrates linear acoustic equations on a 2D grid using the finite-difference time-domain (FDTD) method. It uses a staggered-in-place, staggered-in-time pressure-velocity scheme. The solver is deterministic, using float64 arithmetic and single-threaded numpy stepping to ensure bit-identical outputs on the same platform. It naturally handles reflection, diffraction, interference, and refraction through inhomogeneous media.

  11. Overview of phonometry metrology and calibration

    The phonometry library provides a framework to convert software-printed levels into formal measurements by addressing three critical requirements: data qualification (determining if a record should be averaged), physical meaning (calibration), and uncertainty analysis (determining the potential error). It supports two primary reference frames: physical dB SPL (established via IEC 60942 calibrator tones) and digital dBFS (relative to full scale).

  12. Overview of the phonometry library

    phonometry is a library used to compute acoustic quantities based on the text of international standards, including ISO, IEC, ANSI, ASTM, the CNOSSOS-EU annex to Directive 2002/49/EC, and ICAO/ECAC aircraft documents. Every metric in the library explicitly names the clause of the standard it implements.