Fruit-Strumen-Tation

Michael Hammond, c. 2009

Fruit-Strumen-Tation is a small, freeware application that models instruments using a variety of fruits as the resonating bodies. In creating the application, samples of Watermelon, Mango, Papaya, Spaghetti Squash, and Cantaloupe were collected and used to build a set of virtual Fruit-Struments. The user interface (shown below) lets you tweak three parameters as you create your own unique fruit-strument:

  • Instrument: These include plain vanilla StifKarp (a stringed instrument), ModalBar (tuned, percussive instrument), pre-recorded guitar samples, and the built-in microphone.
  • Excitation mode: Plain impulse response, stabbing of the fruit body, slow mutilation of the inner fruit fiber, and flicking of a rigid object impaling the fruit.
  • Fruit type: Watermelon, Mango, Papaya, Spaghetti Squash, and Cantaloupe.
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Multiple modes of each parameter can be selected, and the output is randomized. Additionally, if no instrument modes are activated, the natural impulse response of the fruit will be played and conversely, if not fruits are selected, the natural ("disembodied") instrument sound will be played. To keep things simple, you play the instrument by striking any key on your keyboard!

Fruit-Strumen-Tation GUI

Inspiration

After seeing So Percussion perform on Sammy the Squash at the Kitchen, I began thinking about ways to create virtual instruments using the beautiful sounds hiding inside organic objects. I really wanted to find out what a stringed instrument with a fruit or vegetable body would sound like. I've seen carrot ocarinas before, but the idea of a stringed fruit is especially cool because in most cases it is actually physically impossible. The string tension would likely cause the soft fruit to buckle.

Another reason I undertook this project is that I wanted to gain experience using contact microphones. My friend Scott Smallwood gave me some great tips on how to build cheap contact mics, and lo and behold, they actually sound pretty good!

How

After obtaining the fruit and building my contact microphones (out of cheap piezo units from Radio Shack), I set about determining the best method of exciting the fruit. I knew I wanted to include one "ideal" impulse response in my collection of sounds. After reading a paper by Yamamoto, H., et. al., in which the authors used the impulse responses of apples and watermelons to determine ripeness, I was intrigued by their method of exciting the fruit with a wood ball pendulum. This was how I obtained my "ideal" impulse. I realize that the best way of determining the body impulse response is to record at a slight distance in an anechoic chamber with one of those fancy force hammers, but alas, I was forced to settle for contact mics. Some pics:

The Fruits
Mic on Melon

In addition to using the pendulum, I also stabbed the fruit with various objects (mini dowels, knife, paperclips). The "stab" option in the GUI calls up this sample set and randomly chooses one of these files to use as the body model. For "fiber," I slowly cut into the fruit to excite the juicy part (gross! but cool!). For "flick," I channeled So Percussion and flicked objects impaling the fruit.

Achieving good real-time synthesis in Chuck was a challenge. I found it best to use a small FFT size because the real time computation could stall ChucK if the FFT were too large. However, having a small FFT necessitated a tradeoff in sound quality. In the current version, I tried to strike a balance between these considerations. Additionally, I found the magnitude-only cross-synthesis to be much more interesting than the seemingly more straightforward convolution. Convolve at your own risk!

One last feature: I learned that commuted synthesis models change body size by directly changing the playback rate of the impulse response of the instrument body. In order to play the instrument body size, use the accelerometers built in to your mac. Left == Larger body size and Right == smaller.

Running

To run Fruit-Strumen-Tation, download the files, open the directory and double click the shell script titled "fruit." Alternatively, you can just check out the ChucK code here. However, you'll need the processing app to change which sounds you're playing. Unfortunately, Fruit-Strumen-Tation remains untested on non-Macs at this time.

Sound Samples

Fruity Music

In this example, I used Fruit-Strumen-Tation to its fullest capacity. Some of my favorite sounds exploited in the recording are "fiber" sounds with modulating body size, a low stifKarp sound alternating with the natural sound of the fiber impulse, very fast ModalBar playing (to me the modal bar fruit models sound a lot like an mbira or kalimba fashioned out of a gourd, especially in "flick" mode as it approximates the odd trinkets African mbira players often use to adorn their instruments.) This is several performances edited together.

References