Source: https://jmrplens.github.io/phonometry/start/ # Start phonometry computes acoustic quantities from the text of the standards that define them — ISO, IEC, ANSI and ASTM, the CNOSSOS-EU annex to Directive 2002/49/EC, and the ICAO and ECAC aircraft documents — and every metric names the clause it implements. What that buys you, and how it is checked, is [Why phonometry](https://jmrplens.github.io/phonometry/why-phonometry/). Five short pages, meant to be read once before anything else. Each answers one question, and they are in the order the questions arrive. **Can I install it and get a number out?** [Getting Started](https://jmrplens.github.io/phonometry/getting-started/) installs the library, runs a first one-third-octave analysis on a synthetic signal, then anchors that analysis to a calibrator tone so the levels are decibels re 20 µPa rather than decibels re nothing, reduces them to one A-weighted level, and states what a recording must satisfy for any of it to hold. It stops one stage short of a meter: the Fast and Slow ballistics, $L_{AE}$, $L_{Cpeak}$ and the percentile levels are in [Build a sound level meter](https://jmrplens.github.io/phonometry/signals/sound-level-meter/), which runs the whole chain end to end on one page, and [Calibration and dBFS](https://jmrplens.github.io/phonometry/signals/metrology/calibration/) is the deep guide behind the one step that matters most. **I have a job, not a subject. Which page is it?** [What do you need to measure?](https://jmrplens.github.io/phonometry/start/tasks/) indexes the library by the task instead of the topic: measure a reverberation time, check a wall against a building code, rate a machine's sound power, decide whether a worker is over the exposure limit. **Where is the thing I came for?** [All guides](https://jmrplens.github.io/phonometry/) is the map: every guide in the library, grouped by the topic it belongs to, with a line on each. **Should I trust the number?** [Why phonometry](https://jmrplens.github.io/phonometry/why-phonometry/) sets out what the library is for and how it is validated against the standards it implements, with the tone-burst check worked through against the acceptance limits. **Who is answerable for it, and how do I cite it?** [About](https://jmrplens.github.io/phonometry/about/) states who maintains it, how to cite it and under what licence. ## Two things to settle before any guide works **Which reference frame a level is in.** A level is either *physical*, in dB SPL, anchored by a recorded calibrator tone or by a known microphone sensitivity, or *digital*, in dBFS relative to full scale. The two are not interchangeable, and most guides assume the first: a level function handed raw soundcard samples returns a number whose reference is arbitrary, which looks exactly like a valid answer. [Calibration and dBFS](https://jmrplens.github.io/phonometry/signals/metrology/calibration/) settles it. **That almost everything downstream consumes bands.** Below the raw signal there is one decomposition: fractional-octave bands whose −3 dB edges sit on the ANSI S1.11 / IEC 61260-1 nominal frequencies. A loudness model, a room parameter and an environmental rating all start from it, which is why the band-filtering page is the one prerequisite that turns up everywhere: [Filter Banks](https://jmrplens.github.io/phonometry/signals/filters/filter-banks/). ## What a guide looks like Worth knowing before opening one, because it is what lets you decide in thirty seconds whether a page answers your question. Every guide opens with the standard it implements, the quantities that standard defines and the assumptions the implementation makes; then comes runnable code and the figure it draws; and it closes with a "What this guide covers" block that states plainly which clauses, annexes and methods are implemented and which are not. The last of those is the part a reviewer asks about, and it is deliberately the part written most bluntly. ## If you already know what you need - A first measurement carried end to end: [Build a sound level meter](https://jmrplens.github.io/phonometry/signals/sound-level-meter/). - The whole inventory, by topic: [All guides](https://jmrplens.github.io/phonometry/). - A symbol you have but cannot name: the [glossary](https://jmrplens.github.io/phonometry/reference/glossary/), with its unit, its defining clause and the guide that computes it. - Evidence that a number is defensible: the [conformance report](https://jmrplens.github.io/phonometry/reference/conformance/), which prints each standard's own expected value beside the computed one. - A printed expected value that disagrees with the library: the [errata registry](https://jmrplens.github.io/phonometry/reference/errata/), which says which of the two is wrong and why. The assumed starting point is Python 3.13 or newer with working NumPy and SciPy, and enough acoustics to know what a one-third-octave band and a sound pressure level are. ## What Start is not This is not a tutorial series, and it is not the API. Function signatures and argument types are in the generated API reference. The derivations, the numerical conformance report, the errata register for defects found in the published standards themselves, the glossary of symbols and the bibliography are all in [Reference](https://jmrplens.github.io/phonometry/reference/). And the acoustics itself is assumed rather than taught: the guides explain the method a standard prescribes and why it is written that way, not what a decibel is.