Guides
Every guide on this site follows the same shape: the standard it implements, the quantities that standard defines, the assumptions the implementation makes, then runnable code and the figure it draws. Nothing here is a survey of the field; each page is the working documentation of a module, written so that a result can be defended clause by clause rather than trusted.
This page is the map. Sixty-six guides sit in nine areas, and each area has its own overview page with the longer story of how its pieces fit together. If you are arriving without a specific question, read Getting Started first: it runs one signal through the whole processing chain and gives the vocabulary the rest of the guides assume. If you already know the quantity you need, the glossary lists every symbol with its unit, its defining standard and the guide that implements it.
Two pointers before the list. Function signatures live in the API reference, which is generated from the docstrings and is not repeated here. Derivations, design decisions and the numerical evidence live in Reference: the theory pages explain why a formula is the one it is, and the conformance report shows the standard’s own expected value next to the computed one.
Filter banks, weighting, levels, spectra, calibration and uncertainty. This is the chain that turns a digital signal into a standards-compliant number, and every other area consumes it: a loudness model needs calibrated band levels, a room parameter needs a filtered impulse response, an environmental rating is an adjusted Leq. Implements IEC 61260-1, ANSI S1.11, IEC 61672-1, ISO 7196, IEC 61252, ISO 1996-1, IEC 60942, ISO 18233 and the GUM.
- Build a sound level meter: the whole area assembled end to end on one runnable page, from the calibrator tone to the reported levels.
- Filter Banks: the five filter architectures, their frequency responses, band decomposition and zero-phase offline filtering.
- Block Processing: stateful streaming analysis that carries filter state across buffers, for signals that never fit in memory.
- Multichannel and Performance: vectorized analysis of many channels at once, with the (channels, samples) convention and performance notes.
- Frequency Weighting (A, B, C, D, G, AU, Z): the IEC 61672-1 ear-response curves, ISO 7196 G-weighting for infrasound and the historical B and D curves.
- Time Weighting: the Fast, Slow and Impulse exponential ballistics of IEC 61672-1.
- Integrated and Statistical Levels: Leq and LAeq, the percentile levels L10/L50/L90, LCpeak and SEL, noise dose, Lden and the ISO 1996-1 rating levels.
- Calibrated spectral analysis: the Welch power and cross-spectral estimators with their random errors, chi-square confidence intervals and fractional-octave smoothing.
- Multiple and partial coherence: the ordinary, multiple and partial coherence of several correlated sources driving one response, and which source dominates each band.
- Time-frequency analysis: the calibrated STFT spectrogram in absolute dB SPL, and the zoom FFT that resolves tones closer than a practical FFT bin.
- Cepstrum, echoes and the envelope spectrum: quefrency analysis, echo detection with the reflection coefficient read off the cepstral peak, liftering and the envelope spectrum.
- Time synchronous averaging: extraction of a periodic waveform of known period, the comb filter that describes it and the choice of the number of averages.
- Correlation, time delay and envelope: correlation with its random errors, time-delay estimation by direct correlation and the GCC weightings, and the Hilbert envelope.
- Test signals and sample-rate tools: IEC 60268-1 tone bursts with exact gating, colored noise with an exact slope, resampling with a stated anti-alias specification and fractional delay.
- System measurement: complementary Golay pairs, sweeps shaped to an arbitrary target magnitude spectrum, and Kirkeby-regularized inversion of a measured response.
- Calibration and dBFS: physical SPL calibration from a calibrator tone or a known sensitivity, and the digital full-scale mode.
- Measurement uncertainty (GUM and Monte Carlo): the law of propagation of uncertainty and the Monte Carlo method, with expanded uncertainty and coverage intervals.
- Data qualification: the reverse arrangement and runs tests for stationarity, and the Rice level-crossing and peak statistics with the irregularity factor.
Loudness, sound quality, speech intelligibility, hearing and exposure. Where the core area asks how much sound there is, this one asks what a listener makes of it: how loud it seems, how sharp or rough or annoying, how much of a talker survives the room, and how much hearing a working life in that noise costs. Implements ISO 532-1/-2/-3, ECMA-418-1/-2, ISO 226, DIN 45692, IEC 60268-16, ANSI S3.5, ISO 7029, ISO 1999 and ISO 9612.
- Loudness: loudness in sones by Zwicker, Moore-Glasberg, the time-varying ISO 532-3 model and the ECMA-418-2 Sottek Hearing Model, plus the ISO 226 equal-loudness contours.
- Sound Quality Metrics: sharpness in acum, and the ECMA-418-2 tonality, roughness and fluctuation strength.
- Prominent Discrete Tones (ECMA-418-1): the tone-to-noise ratio and prominence ratio, with their frequency-dependent prominence criteria.
- Objective audibility of tones in noise (ISO/PAS 20065): the critical-band masking level, the masking index and the audibility of a tone above the masking threshold.
- Psychoacoustic annoyance and fluctuation strength: the Fastl and Zwicker annoyance model built from loudness, sharpness, roughness and fluctuation strength.
- Speech Transmission Index (STI): the modulation transfer function, the indirect method from an impulse response and the direct STIPA measurement.
- Speech Intelligibility Index: the one-third-octave SII with its band-importance function, self-masking and upward spread of masking.
- Objective Intelligibility (STOI and ESTOI): the two correlation-based measures for time-frequency weighted noisy speech.
- Hearing threshold (age and reference zero): the age-related threshold distribution of ISO 7029 and the ISO 389-7 reference threshold of hearing.
- Noise-induced hearing loss (ISO 1999): the permanent threshold shift as a function of level, duration and frequency, combined with the age component.
- Occupational Noise Exposure (ISO 9612): the task-based, job-based and full-day strategies for LEX,8h, with the uncertainty budget and the upper limit.
Room parameters, background noise, field and laboratory insulation, and prediction from element data. Two questions run through the area: how a room treats the sound made inside it, and how much of the sound made next door gets through. Implements ISO 3382-1/-2/-3, ISO 16283-1/-2/-3, ISO 10140, ISO 717-1/-2, EN 12354-1 to -6, ISO 12999-1, ISO 10052 and ANSI/ASA S12.2.
- Room Acoustics: impulse-response acquisition and the room parameters EDT, T20, T30, C50, C80 and Ts, plus open-plan speech metrics and reverberation-room absorption.
- Image sources and the steady-state room field: the deterministic image-source impulse response of a rectangular room, the room constant, critical distance and Schroeder frequency.
- Room-noise criteria (NC / RC Mark II): the ANSI/ASA S12.2 Noise Criteria rating by tangency, and the Room Criteria Mark II rating with its rumble, hiss or neutral tag.
- Reverberation-time prediction (Sabine, Eyring, Arau): five statistical-acoustics models from volume, boundary areas and surface absorption, including the air term.
- Sound absorption in enclosed spaces (EN 12354-6): the total equivalent absorption area of a room from its surfaces, objects and air, and the reverberation time that follows.
- Field Insulation Measurement and Ratings: airborne, impact and façade insulation in the field with their weighted single-number ratings, uncertainty and the survey method.
- Laboratory Insulation Measurement: ISO 10140 element characterisation, insulation by intensity, floor-covering improvement on a mock-up and laboratory flanking transmission.
- Predicting Sound Insulation (EN 12354): in-situ airborne and impact insulation from element data, with flanking paths, façade insulation and outdoor radiation.
- Predicting Panel Sound Insulation: the mass law and coincidence dip, double walls, slits and apertures, plate radiation efficiency and point mobilities.
- Dynamic stiffness of resilient materials (EN 29052-1): the stiffness per unit area under a floating floor from the load-plate resonance, with the enclosed-gas term.
Absorption, airflow resistance, the impedance tube, porous models and scattering. What a surface does to the sound that reaches it, measured in a laboratory or predicted from the material parameters. Implements ISO 354, ISO 11654, ISO 10534-2, ISO 9053, ISO 17497-1/-2, ISO 13472 and EN 29052.
- Acoustic Materials: the weighted absorption rating and its class, airflow resistance and resistivity, and the impedance-tube surface impedance, absorption and transmission loss.
- Porous and Multilayer Absorbers: the Delany-Bazley, Miki and Johnson-Champoux-Allard models, the transfer-matrix multilayer solver with perforated, microperforated and membrane layers, and the random-incidence integral.
- Surface Scattering, Diffusion and In-situ Absorption: the random-incidence scattering coefficient, the autocorrelation diffusion coefficient, and in-situ road-surface absorption.
Mobility and frequency-response functions, isolators, radiated power, junctions and human vibration. The area covers the path a machine takes into a structure and out again as airborne sound, and the separate question of what vibration does to the person exposed to it. Implements ISO 7626, ISO 10846, ISO/TS 7849, EN 15657, EN 12354-5, ISO 2631-1/-5, ISO 5349 and ISO 8041.
- Mechanical mobility and the FRF family (ISO 7626-1): receptance, mobility and accelerance with their reciprocals, conversion between them, and the closed-form single-degree-of-freedom resonator.
- Bending-wave transmission at plate junctions: the wave-approach transmission coefficients for rigid X, T, L and in-line junctions, their diffuse-field average, and the coupling loss factor and vibration reduction index.
- Transfer stiffness of resilient elements (ISO 10846): the dynamic transfer stiffness and loss factor of an isolator by the direct and indirect methods.
- Sound power from surface vibration (ISO/TS 7849): the radiated power from the surface-averaged velocity level and the radiation factor, with the Part 1 upper limit and the Part 2 engineering value.
- Structure-borne sound power of equipment (EN 15657): the reception-plate method and the plate-independent source quantities, equivalent blocked force, free velocity and source mobility.
- Installed structure-borne sound (EN 12354-5): the coupling term from source and receiver mobilities, the installed power and the per-path sound pressure level in the receiving room.
- Human Vibration: whole-body and hand-arm exposure with the ISO 8041-1 weightings, the weighted r.m.s. and dose measures, and the daily exposure A(8).
- Multiple-shock whole-body vibration (ISO 2631-5): the seat-to-spine transfer function, the acceleration dose, and the cumulative stress variable behind the lumbar injury probability.
Outdoor propagation, barriers, refraction, aircraft, rotorcraft and wind turbines. Everything here concerns sound that has to travel a long way before it is assessed, so the atmosphere, the ground and the source’s own motion all enter the answer. Implements ISO 9613-1/-2, ISO 1996-1/-2, ISO/PAS 1996-3, NT ACOU 112, ICAO Annex 16, IEC 61265, SAE ARP 5534, ECAC Doc 29/32 and IEC 61400-11.
- Outdoor Sound Propagation: atmospheric absorption and the ISO 9613-2 general method, with a per-term octave-band attenuation breakdown.
- Spherical ground effect and advanced barriers: the Weyl-Van der Pol reflection coefficient over finite-impedance ground, and wave-theoretic barrier diffraction.
- Atmospheric refraction: rays and the GFPE: effective sound-speed profiles, curved rays with a closed-form shadow-zone distance, and the GFPE relative-level field.
- Impulsive-sound prominence (NT ACOU 112): the predicted prominence of each impulse from its onset rate and level difference, and the adjustment added to LAeq.
- Aircraft noise: Effective Perceived Noise Level: perceived noisiness and PNL, the tone correction, the duration correction and the measurement-system verifier.
- Rotorcraft noise: the hemisphere method: the hemisphere source model with its propagation adjustments, flight-condition interpolation, and the single-event contours.
- Wind-turbine noise: sound power and tonal audibility: the apparent sound power level referred to the rotor centre, and the tonal audibility chain that decides whether a tone is audible.
Levels referenced to 1 micropascal, ship radiated noise, pile driving, ambient noise and transmission loss. The reference quantities differ from the airborne ones, so this is the one area where a level cannot be read across without conversion. Implements ISO 18405, ISO 17208-1/-2, ISO 18406 and JOMOPANS-ECHO.
- Underwater acoustics: radiated noise and pile driving: the ISO 18405 reference levels, the ship radiated noise level and equivalent monopole source level, and single-strike and cumulative pile-driving exposure.
- Underwater sound propagation: spreading plus volume absorption, the speed of sound in sea water, the sonar equation, seabed reflection loss and the ambient-noise spectrum.
Sound power, intensity, emission declarations, electroacoustics and programme loudness. What a source emits rather than what a receiver gets, plus the electroacoustic chain that reproduces or measures it. Implements ISO 3741, ISO 3744/3746, ISO 3745, ISO 9614-1/-2/-3, IEC 61043, ISO 4871, IEC 60268-3/-4/-5, ITU-R BS.1770-5 and EBU R 128.
- Sound Intensity (p-p): two-microphone intensity with the field indicators that qualify the measurement.
- Sound Power: the sound power level by five routes, enveloping surface, reverberation room, anechoic room and two grades of intensity scanning.
- Electroacoustics: distortion and frequency response: harmonic and intermodulation distortion, THD+N and SINAD, dynamic range, the H1/H2 frequency-response estimators and the sensitivity conventions.
- Swept-sine distortion and phase utilities: harmonic separation from one exponential sweep, THD against excitation frequency, and minimum phase, group delay and excess phase.
- Industrial Noise Control: Silencers, HVAC and Enclosures: reactive silencers by the transmission-matrix method, duct attenuation and flow noise, and enclosure insertion loss.
- Programme loudness and true peak: K-weighting and gated integrated loudness in LUFS, the momentary and short-term meters, the loudness range and the true-peak level.
A deterministic 2D finite-difference time-domain solver, validated against analytic oracles rather than a standard. It is the one area with no governing document, so its evidence is the closed-form solution it reproduces.
- 2D FDTD wave simulation: a staggered pressure-velocity grid with Gaussian, tone and arbitrary-signal sources, rasterised obstacles, rigid, impedance and absorbing boundaries, and a frozen result carrying probe histories and field snapshots.