Sonificación en la práctica

La sonificación con fines educativos, en la práctica, es un proceso de exploración de todas las posibilidades que responde esencialmente a la pregunta: "¿Cómo puedo utilizar el sonido para resaltar o demostrar una o más informaciones o conclusiones derivadas de un movimiento, una medición o un fenómeno que existe, ha ocurrido o se está desarrollando a lo largo del tiempo?". Los datos existentes a nuestra disposición, las condiciones y los métodos de su recopilación, así como el propósito educativo para el que se destina la sonificación, son los factores determinantes para su uso eficaz.

Los aspectos que se describen a continuación configuran la relación entre las necesidades educativas y el concepto de sonido, así como su organización estructurada a lo largo del tiempo, es decir, el concepto de música.

Aspectos de la enseñanza con la sonificación como práctica musical

La indiscutible conexión entre el sonido y los números —en concreto, el concepto de descomposición del sonido en frecuencias o armónicos— proporciona un marco suficientemente estructurado para la enseñanza interdisciplinaria mediante el sonido, dentro del cual se pueden abordar todos los aspectos de STEAM (Ciencia, Tecnología, Ingeniería, Arte y Matemáticas). Dado que el concepto de tiempo define el fenómeno sonoro, el acto representacional de un efecto de sonido no puede sino estar en el centro de cualquier enfoque pedagógico. En consecuencia, la disposición organizada de los elementos sonoros en el tiempo de forma armoniosa —tanto en términos de ritmo, intensidad, timbre, altura y su ubicación posicional en la escala musical, diatónica o no— constituye un resultado musical. Esta organización racional puede servir como campo de experimentación en la composición musical, mientras que la parametrización de todos los conceptos anteriores puede enriquecer cualquier objetivo educativo que dependa de la evolución de un fenómeno a lo largo del tiempo o de la conversión de datos en sonido.

Por lo tanto, podemos distinguir razonablemente el concepto de sonificación con fines educativos en tres enfoques básicos:

• El simbólico

• El matemático

• El adaptativo

Sonificación simbólica

La reproducción de las características del sonido, a saber: tono, intensidad, timbre, frecuencia de repetición (si la hay) y duración —que están vinculadas a conceptos, términos y cantidades científicas sin estar asignadas lógicamente a un conjunto de datos (mapeo de datos)— constituye el objeto de la sonificación simbólica.

Un ejemplo sencillo sería “pintar con sonido” una nube gris usando ruido de baja frecuencia y una nube blanca usando ruido de alta frecuencia. Otro ejemplo sería una clase de estudiantes representando el sonido de la lluvia golpeando aleatoriamente sus uñas contra sus pupitres. Otro ejemplo que relaciona la composición con la representación musical es el leitmotiv. Un leitmotiv es un tema melódico breve que consta de unas pocas notas específicas que, como motivo (patrón) único, se asocia con un personaje de una ópera y es interpretado por la orquesta, particularmente en las óperas de Wagner. El leitmotiv de un personaje lo evoca a lo largo de toda la obra, ¡tanto si el personaje está en escena como si no! Trasladando esto a una serie de datos, dicho leitmotiv podría reemplazar el sonido esperado de un valor bajo o alto prominente (o un valor específico o incluso un rango de valores) sin tener ninguna coherencia ni surgir de los datos vecinos.

Sonificación matemática

Cuando el tono, la intensidad, el timbre, el ritmo (si lo hay) y la duración, como características del sonido, se relacionan con una serie de mediciones de datos vinculadas a un término físico o un concepto científico, forman un mapa lógico de una o más partes de dicha serie (mapeo directo de datos). El resultado sonoro de esta correspondencia es la sonificación matemática.

Un ejemplo que ilustra perfectamente la distinción anterior, principalmente mediante el uso del ritmo, es el mecanismo de indicación sonora de la distancia entre un coche y el que está a su lado al aparcar, una función presente en muchos vehículos. La frecuencia de repetición de esta señal acústica momentánea forma un patrón repetitivo cuyo ritmo varía (lento-rápido) en función de la proximidad al obstáculo, que es detectada con gran precisión por un sensor.

Para comprender la diferencia entre representación simbólica y matemática, podemos adaptar los ejemplos anteriores como actividades sin conexión en el aula. En el ejemplo de las nubes, la sonificación matemática se produciría si definiéramos un umbral de color para el blanco o el gris y representáramos las gotitas que las componen con millones de partículas de frecuencia de duración mínima (nebulosas sonoras). En el ejemplo de la lluvia, tendríamos una sonificación matemática si los estudiantes representaran con absoluta precisión, una por una, cada gota de lluvia en un momento y área específicos. Finalmente, en el ejemplo del estacionamiento, tendríamos una representación simbólica si los ojos de los estudiantes asumieran el rol de sensor, donde los datos se estimarían visualmente sin una medición matemática absoluta.

Sonificación adaptativa

Se trata de un diseño sonoro o composición musical (ampliando este concepto), resultante de la sonificación matemática en la que, sin embargo, se utilizan de forma creativa métodos de representación estética del sonido para cumplir los objetivos de enseñanza al describir conceptos de aprendizaje.

Además, el análisis de los métodos de mapeo de datos junto con la escala diatónica abre un campo fructífero para explorar herramientas didácticas que permitan procesar el sonido en términos de composición musical. El uso de MIDI para el procesamiento del sonido o el resaltado de motivos musicales —que pueden servir como punto de partida para la creación de composiciones musicales— amplía perfectamente la sonificación adaptativa. De hecho, la representación gráfica de datos (visualización gráfica) puede transformarse creativamente en sonido al tratar la visualización como un esquema bidimensional, o incluso una fotografía como una imagen tridimensional. El resultado se conoce como "sonificación esquemática".

Este enfoque adaptable amplía el acceso al resultado auditivo de la sonificación de datos a una amplia gama de grupos de edad y niveles educativos, invitando a educadores de otras disciplinas, como Arte, Teatro y Música, a participar activamente en la enseñanza interdisciplinaria. Un ejemplo de este enfoque se ha implementado en el escenario "Sonidos de las Estrellas" en colaboración con el Observatorio Nacional de Atenas (comunidad: Ήχοι των Άστρων). Este escenario forma parte del repositorio de escenarios de aprendizaje SoundScapes .

El protocolo MIDI. ¿Por qué es útil para la sonorización en la escuela?

El protocolo MIDI (Interfaz Digital para Instrumentos Musicales) se introdujo a principios de los años 80 como un lenguaje de máquina que permitía la interconexión de instrumentos analógicos y, posteriormente, digitales. Este lenguaje interpreta diversos aspectos de la interpretación y la notación musical en formato electrónico.

MIDI permite al usuario recibir, transmitir, almacenar y editar señales producidas electrónicamente que corresponden a diversos aspectos de la música. Los parámetros principales de estos aspectos incluyen el inicio y el final de las notas, la velocidad, el timbre y el tono. Todos estos parámetros se pueden almacenar como código en forma de línea de tiempo dentro de un archivo MIDI. Un archivo MIDI se asemeja al "programa" en forma de cilindro giratorio o papel perforado, como los que se usaban en las cajas de música de finales del siglo XVIII o en los pianolas de principios del siglo XX, que eran autómatas musicales. Esta característica puede resultar enormemente útil con fines educativos, ya que numerosas aplicaciones, sensores y programas MIDI están ampliamente difundidos por internet.

Sin embargo, es la capacidad de editar la salida como partitura musical o como parte de una composición polifónica lo que convierte a MIDI en una herramienta educativa excepcionalmente potente. En las presentes páginas de la wiki se muestran ampliamente sensores que utilizan MIDI.

Componentes de sonificación

Una actividad de sonificación consiste en el diseño y la construcción de un sistema de sonificación. Un sistema de sonificación se puede lograr de muchas maneras diferentes, pero siempre se deben considerar 3 componentes:

1) DATOS DE ENTRADA;

2) MAPPING PROTOCOL;

3) AUDIO OUTPUT;

Input Data

In a sonification system, which is our final product, the data is the source of the sound engine, and some particular sounds will be the output. The inputs and outputs are mapped onto each other following a protocol that establishes which sounds are played according to which data. So first we need to know and understand the data we want to sonify. We must know what we want to say with our system - what we will talk about. We must know how the data change (usually we have time based data but there can also be spatially referenced data, like maps) and what characteristics of its behavior we want to represent. For example if you have a single value (like luminosity of a star, linear position of a car, amount of likes in a youtube channel, number of new posts on wikipedia, etc) you can choose to play a sound when this value is more than a certain threshold value, or play a sound that gets louder when the values becomes higher, or a sound when the values are raising or decreasing in time. In some cases it is useful to determine the highest and the lowest value within the whole range of values available. In terms of outputs this can help define a “container” of initial values that can define the range of deviations in the output. We can highlight certain features of data. There are many types of data. The most common are: 

Single data: indicating a state ON-OFF (boolean data).

A single data value covering a range of values: usually mapped to a single sound or sound feature like the pitch, or bpm (beats per minute), or an effect, but it can control more than one feature or sound at once.

Multiple data: more than one data of the previous type. Usually there are many types of data collected at the same time so these data sets consist of several layers of synchronized data.

Sound has the advantage over visual perception that more layers of data can be perceived at the same time. Changes in patterns are more easily detected listening than looking at. Especially if the amount of data is very large. So, in sum, we need to consider the data we have, how they evolve in time, how they are arranged and what are the salient parts we want to use to feed our sonification system. We have to ask ourselves “what will the sound mean?” We need to understand that data is not the message! We must metabolize the data and their behavior and find what message will be triggering sound.

And, therefore, before this we need to ask ourselves what is the purpose of the sonification? Will it be applied continuously, maybe in the background, or just after some time of collecting data, or both?

Real-Time Sonification vs “A Posteriori”

Acording to the use of the sonification system (to analyze or to monitor a certain phenomena) we distinguish two “modes”:

Real-time (to monitor) - a stream of data is sonifed instantly and a sound is produced to display the value and behavior of the data in that particular moment;

“A posteriori” (to analyze) - time-series sonification of a set of pre-recorded data is converted into an audio file that displays the values and behavior of the data over the period of time covered by the time-series. 

These two methods are not mutually exclusive and can eventually display the same sounds. The difference is that in an “a posteriori” sonification, because the sound is produced after the events that originated the data, the parameters of the final piece can be adapted, i.e. the total duration. In a real-time case, you can control the time resolution: that is the time interval at which the sound can change and is played.

Mapping Protocol

The mapping protocol is the core of the sonification system. This is where knowledge of input data must be combined with creativity. According to his/her educational needs, the creator of the sonification system makes choices based on his/her character and artistic taste in translating data sets into sound pieces. The mapping protocol is the process or algorithm or function that associates particular sounds to defined data. It is the set of rules by which output sounds correspond to input data. A simple mapping can consist for example in a direct one-to-one correspondence between each value of an input data to a parameter of an output sound, like the pitch. This component of the system is key because here is where the designer of the system selects certain features of the data to be played in a particular manner, in order to highlight them, or not.

So this mapping consists in associating certain data aspects to different auditory parameters, such as pitch, loudness, timbre, and rhythm. For example, the amplitude of a sound can be mapped to the value of a light resistor, or the frequency of a sound can be mapped to the rate of change of the sea level (tides).

Usually the tendency is to map a single feature of the data to a single parameter of output sound but we humans are generally more capable of perceiving differences in sound if such differences manifest concurrently through different properties. So it is not a bad idea to map the same variable onto different psychoacoustic properties of a sound (pitch and volume as an example of the most evident) if we want to emphasize its change and dynamics.

Our sense of hearing is able to focus on a particular sound in between many others (see the “cocktail party effect”) based on timbre. Our auditory system can process information at a far higher rate than our visual system. For example, while video typically updates at 60 frames per second (60 Hz), standard audio is sampled at 44,100 times per second (44.1 kHz). This means that even a single, brief spike in an audio signal—lasting just one sample—is instantly perceived as a distinct "click." As a result, hearing allows us to monitor multiple layers of information simultaneously, often more efficiently than through visual perception alone .

Audio Output

The output sound of the system will be the first characteristic to be perceived by a user. It is its signature, its flavor. It will interact with the user’s taste and we must be aware of that. It is the auditive wrapping to be perceived by an audience and, as studies on sound perception show, it will immediately and unconsciously provoke a good or bad sensation to the listener. We should therefore get used to producing “nice” sound outputs with the device that will be used, be it a microcontroller buzzer or a pc virtual synthesizer or a DAW (Digital Audio Workstation) connected to speakers. We should practice some music, or at least make some noise!

Considering that sound perception is time-based, sonification is by and large focused on rendering continuous data stream over time: this means that the input data of a sonification system could be also come from another domain, like the profile of a territory (geographical data) but all of them will be transferred onto a representation in time which is sound. Sound exists only in time, as variation of pressure detected by our eardrums and transformed into electrical signals in our brain, or broadly in our nervous system. Without getting into the depth of such a fascinating subject we need to clarify a couple of concepts before we move on. Even those who never played or created music know some of the characteristics of sound that we describe here.

Music and Sound: Basic Concepts

Sound is detected by our brain when a variable pressure stimulates our timpani. This is a small membrane that when moved by air pressure (or water if you find yourself under water) generates electrical stimuli that the brain processes as “sound”. If this variable pressure is oscillating regularly at a certain frequency (a certain number of times per second) we hear a tone. That is why tones (or notes) are measured in Hertz (Hz), or cycles per second.

The human hearing is able to sense tones between 20 Hz and 20000 Hz (this range is unique to each one and usually gets smaller with age). The vibrations of pressure with frequencies lower than 20 Hz or higher than 20000 Hz are inaudible. They are called infrasounds and ultrasounds respectively. We do not hear them but we still can sense them, with the touch sense in the case of infrasound and with temperature sense in the case of ultrasound.

The main characteristics of sound are:

Volume or Intensity or loudness: The power of a soundwave (louder more power, softer less power).

Frequency or pitch: The number of times the sound pressure moves back and forth the timpani in our ears. According to music theory some of these frequencies are called notes in the context of tuning systems.

Timbre: Is the spectral characteristic of sound, its sound quality, its fingerprint, a sense of the “color” of the sound. This is what allows us to distinguish between a trumpet or a guitar when they are playing the same note with the same volume. It also allows us to distinguish between our human voices.

There are several other characteristics that define sound but these are the main ones we can use in this context. Other characteristics that could be easily employed in a classroom for sonification are:

Duration: How long each sound lasts.

Rhythm: How frequently the sounds repeat and in what pattern. For example, a metronome is a device that produces short, evenly spaced sounds at a set number of beats per minute (BPM). Other devices use this characteristic as a sonification output (Geiger counter - Wikipedia) and parking devices for cars.

3D Positioning: The position of a sound source in space - for example if the sound comes from the left or right speaker in a stereo system. Far more complex but basically the same concept, are the surround systems 5.1 or 7.1 up to ambisonic systems where the position of the sound source can be even more detailed by using multiple channels (Ambisonic reproduction systems - Wikipedia)

Context is important

When designing the output sounds we need to consider what will be the audience of the designed system. In which settings they will listen to its sounds. It is impossible to be sure about it and to know the taste of our target listeners but it is convenient to think about it.

What is the profile of the listener? Are they young students? What type of sound would they be interested in hearing? but also in what kind of sound-producing interaction could they be engaged in, according to their skills and potentials? Do they perceive changes in less evident sound features, (i.e. timbre)?

The sounds we produce must be considered in the context where they will be played. They should be able to capture the listener's attention and emerge from the background noise, and if possible, not be perceived as noise or annoying. For example, mapping all the values of a single variable to all the values of frequency in a certain range may sound unpleasant compared to mapping it onto a familiar music scale, like the chromatic scale in the western world. Or manipulating the speed of a regular beat instead of playing random time durations can be more effective. It depends on the listener's attitude and taste, of course. Additionally, it is important to consider the sound designers’ own taste. It is convenient to consider who will be the listener, but, on the other side, it is not mandatory to produce mainstream sounds in order to please the supposed “common taste”.

Apart from taste and esthetic considerations, we need to consider factual conditions: in the case of background continuous sound as a product of a sonification to monitor some data stream we should therefore take into account the potential listener fatigue to that type of sound. We can consider the difference of using familiar sounds (for example even recorded samples of voices and sentences of the target listeners) compared to new and special digitally synthesized sounds. Designers of sonification systems should at least be be aware of the variety of different impacts that their sounds can have upon the listener (synthesized sounds could surprise!).

We need to assemble a diverse toolkit of musical techniques and resources. Sonification designers should ensure their palette of sounds is as rich and varied as the data they aim to represent.

Quality of Output

Sonification should not only be comprehensible but also engaging, ideally offering information as effectively as, or even more clearly than visual graph. The quality of the sonification is equally important. This includes both the technical excellence of the audio and its "musical narrative" - how well it describes the evolution of the data while remaining aesthetically pleasing. While "pleasantness" is subjective, an appealing sonification helps maintain the listener’s attention and ensures the data is effectively communicated, as discussed in the Context is Important section.

Sonifications can use either physical (natural) or digital sounds, depending on resources and approach. Physical sounds come from acoustic sources like the human body, percussion, or traditional instruments, performed through notation, gestures, or improvisation. Digital sounds, however, are generated or processed using computers, digital audio workstations (DAWs), or electronic devices. While technical details like compression, sample rate, or bit depth influence digital audio quality, the key point is the impact of the playback system: a high-quality sound system (e.g., computer speakers) will deliver a richer experience than a simple buzzer.

Musical Quality

The designer should consider what type of narrative he/she is inducing in the listener. That means for example using low and scary sounds to represent parameters of global warming (A Song of Our Warming Planet or The sound of climate change from the Amazon to the Arctic).  As we want to stimulate the user to pay attention to our system output it can also be useful to have a survey about what type of music the listener appreciates. A generally and initially acceptable musical sound, with the least possible chance of being rejected by the majority of recipients, would be the one that would obey the fundamental principles of symmetry and proportion, as these have shaped our common perception of “music" in today's world. 

However, Soundscapes project encourages every approach on sonification if it satisfies the creator's inspiration or cultural demands as well as the aesthetical or informative needs of the audience, or the target group it is addressed to.  

In the following pages, practical ways to implement the above approaches with or without handling data sets coming either from measurements or from sensors, are entitled as: Unplugged activities, Real-time sonification and a posteriori sonification.

References