Source: https://jmrplens.github.io/phonometry/reference/api/metrology/reference-values/ Preferred reference values for acoustical and vibratory levels (ISO 1683:2015). A level in decibels is a ratio to a reference value, so the number means nothing until the reference is known: the same pressure reads 26 dB higher against the 1 µPa of water than against the 20 µPa of air, and the same vibration 34 dB higher against 1 nm/s than against 50 nm/s. ISO 1683:2015 fixes one reference per quantity in three tables, and the level functions of this library count their decibels from them unless the standard they implement names another: - **Table 1**, sounds in air and other gases: sound pressure 20 µPa, sound exposure (20 µPa)² s, sound power 1 pW, sound energy 1 pJ and sound intensity 1 pW/m². - **Table 2**, sounds in water and other liquids: sound pressure 1 µPa, sound exposure 1 µPa² s, sound power 1 pW, sound energy 1 pJ, sound intensity 1 pW/m², sound particle displacement 1 pm, velocity 1 nm/s and acceleration 1 µm/s², and a distance of 1 m for the compound quantities of its note c (a source level re 1 µPa m, for one). - **Table 3**, vibratory quantities: displacement 1 pm, velocity 1 nm/s, acceleration 1 µm/s² and force 1 µN. Its note b adds the 50 nm/s that is also used for structure-borne sound, against which the velocity level comes out close to the associated sound pressure and intensity levels. [`ISO1683_REFERENCE_VALUES`](/phonometry/reference/api/metrology/reference-values/#iso1683_reference_values) holds all of them, keyed by medium and then by quantity, and every value is in the coherent SI unit its row names, so the 20 µPa of air is `2e-05` Pa: ```text from phonometry import metrology p0 = metrology.ISO1683_REFERENCE_VALUES["gas"]["sound_pressure"] p0.value, p0.unit, p0.printed # (2e-05, 'Pa', '20 µPa') ``` Note b of Table 2 gives the offset between the two pressure references, a level re 1 µPa being $10 \lg(20^2/1^2) \approx 26.0$ dB above the same pressure re 20 µPa; [`phonometry.underwater.in_air_to_underwater_spl`](/phonometry/reference/api/underwater/acoustics/#in_air_to_underwater_spl) applies it. The values were transcribed from the Spanish text UNE-EN ISO 1683:2016, which adopts ISO 1683:2015 unchanged, PDF pages 8 and 9 (printed folios 8 and 9), and the quantity names are given here in English. A module that counts its decibels from a different reference keeps it, and names the document it comes from beside it: DIN 45672-2 defines its own 5·10⁻⁸ m/s for railway vibration (Formula (2)), and ISO/TS 7849 and ISO 9611 refer the surface velocity to the same 5·10⁻⁸ m/s, which is the 50 nm/s of note b of Table 3. `scripts/check_reference_values.py` holds the tree to that: a reference value declared in the package either points at this table or says where it was read. > Auto-generated from the source docstrings by `scripts/generate_api_docs.py` (`make api-docs`). Do not edit by hand. ## ISO1683_REFERENCE_VALUES *Constant* (`mapping`). ## ReferenceValue ```python ReferenceValue( quantity: str, medium: str, value: float, unit: str, printed: str, table: str, ) ``` One reference value of ISO 1683:2015, with what it is a reference of. **Attributes** | Name | Description | | :--- | :--- | | `quantity` | The quantity the value is the reference of, in English (`"sound pressure"`, `"vibratory velocity"`). | | `medium` | `"gas"` (Table 1), `"liquid"` (Table 2) or `"solid"` (Table 3, structure-borne sound and vibration). | | `value` | The reference value, in the coherent SI unit `unit` names: 20 µPa is `2e-05` with `unit` `"Pa"`. | | `unit` | The SI unit of `value`. | | `printed` | The value as the table prints it, prefix and all. | | `table` | Where the value is printed: `"Table 1"` to `"Table 3"`, or `"Table 3, note b"` for the 50 nm/s alternative. |