Using a two-track recording for audio
playback and multi-tone control would
synchronize the skull’s jaw to the audio.
The Audacity audio editor was used to
build the sound track, along with the
three jaw tone tracks. With a little trial
and error, the three skulls were moving
their jaws in perfect sync with the song.
The project took about a week to
build and has worked (nearly) perfectly
season after season (Figure 3).
Doing More with Less
The “Singing Trio” was a good and
simple design, but what if I wanted to
build another prop using audio to control
it? I was not looking forward to wiring up
another 50 plus parts for a new spectrum
band detection circuit. There must be a
better way to analyze the audio in my
future projects. Besides, I can never leave well enough
The very next year, Mixed Signal
Integration introduced their “7-Band
Graphic Equalizer” (MSGEQ7). Don’t let
the name fool you, however, since it’s
really a seven-band audio spectrum
analyzer. (The chip is used to run graphic
equalizer displays in consumer audio gear
and the reason MSI picked that name.)
With seven bands, this audio spectrum
analyzer has a wide variety of uses, from
tone detection to real time audio analyzation for
controlling servos and other devices. Figure 4 shows the
By Steven R. Bjork
September 2015 33
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FIGURE 2. First version of
the Singing Trio’s controller.
FIGURE 3. The Singing Trio mounted in the haunt.
FIGURE 4. Frequency response.