Used to replicate the natural response of the human ear. They made tests whose empiric results can provide a general indication about which time constants to use to recognize different classes of sounds: Since in sound level evaluation what is essential is the energetic significance of the sound field, the formula to compute the instantaneous sound pressure level (SPL) in decibels (dB) considers the square of the acoustic pressure instead of just the acoustic pressure:Īfter finding the way to measure and quantify the SPL, scientists of the past asked themselves if it is also possible to recognize particular types of sounds. The value of 20μPa is the absolute audible threshold for a typical human listener for a pure tone sound with a frequency of 1,000Hz (often considered as the threshold of human hearing, roughly the sound of a mosquito flying 3m away). Because of the enormous range of sound amplitude, the pressure is used in logarithmic form, multiplied by 10, and compared to the reference acoustic pressure p0=20μPa. The measure of the over-pressure produced by the acoustic perturbation, in each time instant t, can be called p(t). The collision acquires potential energy, which is transferred to the surrounding air particles as kinetic energy, making them vibrate around their static equilibrium position. When a solid and elastic object (e.g., a tuning fork) is stressed mechanically due to collision, it starts to vibrate. Humans perceive the sound using the eardrum, a membrane that vibrates after a pressure change due to oscillations of the particles in the air that surround us, providing the sensation of hearing.

This article will share the knowledge gained by Sfera Labs, illustrating the main concepts involved, hoping to provide guidance and help to those who intend to develop or integrate software applications regarding sound level evaluation with Raspberry Pi.

Photo 2: Sfera Labs developed and integrated its software to be used with the Exo Sense Pi.

Raspberry pi pa system