Davide Gironi has designed a simple sound pressure level meter (SPL) dB audio meter using an AVR-based ATMega8.
As Gironi notes, a sound level meter or sound meter can probably best be described as an instrument which measures sound pressure level.
“Sound pressure level (SPL) or sound level is a logarithmic measure of the effective sound pressure of a sound relative to a reference value. It is measured in decibels (dB) above a standard reference level. The commonly used reference sound pressure in air is = 20 µPa (rms) which is usually considered the threshold of human hearing,” he explained in a recent blog post.
“Keep in mind that 1 pascal will equal an SPL of 94 dB. Because the frequency response of human hearing changes with amplitude, a weighting have been established for measuring sound pressure. Usually the A-weighting curve is used. A weighting curve is a graph of gain across the frequency range (10Hz to 20kHz).”
On the software side, Gironi uses the Radix-4 FFT library with a matlab script for validation, with two processing scripts provided as a viewer for the data.
Interested in learning more? You can check out the project’s official page here.