Making the Most of What you Have

At the time of this writing I have measured (70+ data points each) 107 ff-holed mandolins, 33 guitars, 6 oval holed mandolins and 8 octave mandolins of a wide variety of quality and build styles.

Sometimes when I haven’t measured a new instrument in a while I get a little antsy and start asking questions. Questions like:

I wonder if I can capture the tone of some of my favorite mandolins from recordings and find out their resonances using FFT?

I already know several recordings where an instrument I am curious about can be heard solo with no other sounds or instruments in there. I also know from experience that if you mute the strings and just “chunk” the deadened strings you will excite the main top and air modes (not the back usually) as well as some others. If you know what you are looking for you can take a FFT of one or more “chunks” and glean this info.

For this purpose I took a recording I am very familiar with and opened it in Audacity.

Once in Audacity I removed the parts that contained other instruments and kept only the parts where I knew this instrument was making a chunking noise and there was no other noises present. That looks like this:

Then I used the spectrum analyzer in Audacity to break these noises down into their component parts like this:

I know from experience that the first and highest main peak here (272 Hz) is this instrument’s A0 (main air resonance), the next peak after that is 374 and one I am still pinning down, but the one after that, 453 Hz, is the main top frequency. That’s 2/3 of the resonances I am currently paying attention to!

I am fairly certain a person could use this technique with any instrument given they are familiar enough with the resonance ranges of that instrument and they can get a clean-enough recording. For me, in my pursuits, this confirms what has already been a pretty solid trend regarding the main air and top resonances. It’s just really cool that I can do with without ever holding the instrument itself!