RPMmtr

Engines, motors and rotating machinery generate periodic sound patterns. RPMmtr analyses those sound patterns to measure RPM (rotational speed) based on state-of-the-art signal processing technology.

The result of this estimation is shown in three different views. The tachometer view displays the rotational speed at a glance. The color of the dent indicates how clear the measurement is. You can swipe the red ring control and improve the result by specifying the expected RPM range.
The tracking view shows the evolution of the rotational speed over time. The accuracy of the measurement is indicated by the size and color of the circles.
Experts can use the spectrogram view: the graph shows the frequency distribution of the sound. Small arrows show the rotational speed. Adjust the axes scaling by a swipe with one finger.

Notice on usage:
The app can estimate the correct rotational speed only in cases if the sound is very clear (i.e. the rotating device generates clear periodic sound patterns with one frequency) and there is no background noise.
RPMmtr is for educational purposes only. We do not take responsibility for decisions taken by the reader based solely on the information provided in this app.