Difference between revisions of "Experiment: Audio Amplitude"

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(Created page with "{{Infobox Experiment | Name = Audio Amplitude | Category = Acoustics | Sensors = Microphone }} The experiment "Audio Amplitude" measures the amplitude of audio recorded fr...")
 
 
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The experiment "Audio Amplitude" measures the amplitude of audio recorded from the microphone. A history of the peak amplitude and the RMS (root-mean-square) of the audio signal are shown.
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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.
  
 
==Requirements==
 
==Requirements==
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==Analysis==
 
==Analysis==
The experiment looks at 50ms recordings at a time to calculate an amplitude. For each of these short samples the peak amplitude is simply the largest value in the recorded data. For the RMS, each sample is squared, then all samples are added up. The square root of this sum is taken and then divided by the number of samples in this 50ms snipped.
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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)).
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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==
 
==Problems and resolutions==
  
* Short bursts of noise (for example a clap) are missed. This may happen if your device is too slow to analyse the audio as fast as it is recorded. You might be able to work around this problem by creating your own version of the experiment and remove the RMS analysis. Only calculating the peak amplitde, but not the RMS should be significantly faster.
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* 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.
  
  
 
[[Category:Built-in experiments]]
 
[[Category:Built-in experiments]]

Latest revision as of 20:43, 15 June 2017

Audio Amplitude
Experiment Audio Amplitude
Category Acoustics
Used sensors Microphone


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.

Requirements

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.


Setup

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.

Analysis

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.