RPM from Sound

for Pocket PC and Windows Laptops

Here is a very accurate way to measure the RPM of your aircraft engine from the sound that it makes.  These free programs run on all brands of Pocket PCs and on any Windows laptop.  Here is how RPM from Sound works.

The sound that an engine makes is complex.  The sound is generally described as a collection of harmonics of a single fundamental frequency, or pitch.  The fundamental frequency itself may not be present in the frequency spectrum, but its frequency can be inferred from the frequency of all the harmonics.  Fortunately, the sharp exhaust note of most aircraft engines has lots of higher-frequency harmonics.  These higher-frequency harmonics are actually a more precise indicator of the exact pitch of the fundamental than the fundamental sound itself.

RPM from Sound listens to the sound from the microphone.  It repeatedly samples the sound over a period of about 3/4 of a second.  From that sample it develops a list of all the peaks in the frequency spectrum.  Each peak corresponds to some harmonic of a fundamental frequency.  The program then searches over all candidate fundamental frequencies to find the one frequency whose harmonics best fit the collection of peaks that were found.  This fundamental frequency is then converted to RPM and displayed on the screen.

RPM from Sound is accurate to within 1 RPM, and can be used in the cockpit, or from a half-mile away.  It is great for checking your tach or for very precise in-flight performance measurements.

There are two versions of the program - one for Pocket PCs and one for Windows laptops:

The installation program for the Pocket PC runs on a Windows computer that is connected to the Pocket PC through ActiveSync (the usual connection for Pocket PCs).

This program is provided by Real-Time Specialties, an embedded systems design contractor, in business since 1984.  It is an example of the kind of real-time programming that we can develop for your custom applications.  For a free no-obligation estimate, call

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