Experiment: Audio Amplitude
The experiment "Audio Amplitude" measures the sound pressure level from audio recorded from the microphone. You need to calibrate the experiment to get reasonable results. phyphox is available for more than 10000 devices, so we cannot do all the calibration ourselves, sorry.
There are no requirements. The microphone is used to measure any sound. However, depending on your requirements you might want to attach an external microphone to your device.
There is no specific setup. Depending on what audio source you want to measure, you might want to aim the microphone at the sound source and try to damp the sound from the environment.
The experiment looks at 100ms recordings at a time to calculate the RMS (which is equivalent to the quadratic sum of its Fourier spectrum). This is then converted to decibels (20*log(x) or to avoid calculating the root of the RMS 10*log(x²)).
The calibration is a very naive one and jsut considers a linear factor to the recorded amplitude. On the logarithmic scale this is an offset, which can be taken from a measurement.
Problems and resolutions
- Even a well calibration experiment is still limited in its accuracy as the experiment does not take into account the base noise, the spectral dependency of the microphone, non-linear responses and directional dependencies. So, this experiment may be suitable for simple educational purposes, but for serios measurements you will either need a dedicated app for you device or, much better, professional equipment.