''a posteriori'' sonification/es

La gran mayoría de los ejemplos de sonificación disponibles en la web son archivos de audio que representan una secuencia de varias capas de datos de un fenómeno determinado (físico, astronómico, metadatos, estadísticas web, economía, parámetros de salud) durante un período de tiempo específico. Se trata de datos almacenados convertidos a un archivo de audio.

Hablamos de «a posteriori» cuando los datos se sonorizan después de haber sido recopilados y almacenados. «A posteriori» proviene del latín y significa «desde atrás» o «desde el pasado». En filosofía, se suele usar para referirse a una afirmación que surge tras la experiencia. Mientras que en la sonificación en tiempo real desconocemos cuál será la siguiente entrada de datos, en la sonificación «a posteriori», al almacenar una secuencia de datos, podemos tomarnos nuestro tiempo para analizarla, ajustar los sonidos de salida y probarlos. El conjunto de datos se transforma en una pieza sonora en su totalidad.

TwoTone

Existen numerosas aplicaciones de sonificación a posteriori disponibles en línea. TwoTone [1] es un programa de Google que permite generar sonidos a partir de datos. Este software cuenta con su propia base de datos, la cual se actualiza periódicamente. Esto demuestra la popularidad de la sonificación.

TwoTone es un software flexible que permite añadir múltiples pistas de datos desde una fuente y asignarlas a una escala específica, seleccionando el instrumento, la octava, el rango, la octava inicial, el tempo, etc. El usuario también puede añadir pistas de audio desde la base de datos, cargar sus propias pistas y grabar sonido con el micrófono.

Usando TwoTone

To start playing with it, TwoTone comes with a database that the user can explore to test the software features. After you feel comfortable with it, you can import your own data.

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a posterior sonification example with twotone.

Prepare and import data

After collecting and storing the data you want to sonify (either with a device like a microcontroller, a computer, a smartphone, from a web source, or by hand) you have to prepare the data in the right format. For instance, imagine you have collected air pollution data from an air quality station:

1. Open Excel (or another equivalent spreadsheet software) and write the first row as headers. Use simple headers like "Timestamp" and "CO2". This row will be treated as the names of the data fields.
2. The rows below the headers should contain the actual data.
3. Save your file in .csv format.

In this example, the data file should look like the following:

TwoTone file format.

When selecting a data source, upload your file in the rectangular box, either by clicking it and browsing your local folders or by dragging the file into it:

TwoTone upload file

Data from the Web

There are many certified/credited sources of data online that you can use in your sonification projects. Here is a list of suggestions:

• Our World in Data - comprehensive online resource that provides accessible data and research on global development, covering topics such as health, education, and the environment.
• Pordata - a Portuguese online database that offers statistical information on various aspects of Portugal's society, economy, and demographics, facilitating access to data for research and analysis.
• Datos Clima- Spanish platform that provides access to climate data and information, focusing on the impacts of climate change and promoting awareness and research on environmental issues.

Collect and store data with micro:bit

There are many different ways to collect and store data. Using a microcontroller can be very helpful if you are designing your own data collection device, and the micro:bit is a great choice, as it is flexible and easy to use. If you are not yet familiar with the micro:bit microcontroller, we recommend you to start by reading the real-time sonification SoundScapes wiki page where we introduce the readers to quick tutorials and examples.

To store data on the micro:bit you need first to install the Makecode extension datalogger:

Install datalogger extension

Using internal sensors

The following is an example of how you can program the micro:bit to collect and log data on the board. The example logs the acceleration strength input, but another internal sensor (sound level, light level, compass heading, temperature) or external sensor can be used.

To access the data, open the micro:bit in you file explorer/manager and open the file MY_DATA.HTM. Notice you can also copy it, save it in .csv format (ready to import to TwoTone), or visualize it.

Access logged data

Using external sensors

If instead of using a micro:bit sensor you want to collect data from an external digital/analog sensor on a micro pin or using for instance the I2C protocol (all of these blocks can be found under the advanced categories) you can use the same program but simply replace the acceleration input block with the corresponding block as follows:

Digital read pin

Analog read pin

i2c pin

Attention to the pin number or the i2c address!

a posterior sonification with micro:bit

If you are not yet familiar with the SoundScapes sonification extension for Makecode micro:bit we recommend you to visit the wiki section dedicated to it.

When you collect data with the micro:bit for playing a posteriori you can save it an array. The following example collects light-level data for 10 seconds (one value per second) while mapping it to the Middle D Minor scale on 2 octaves, and plays the data after collection, each tone sequentially for 1000 ms:

The map function for arrays returns an array of integer numbers from mapping an input array to a specified music scale and number of octaves. Any array of numbers can be used as input. This is useful for a posteriori sonification when you want to sonify the data after collecting it.