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- First, download the Pd patch for this
lab. Open
the Pd patch in Windows by double-clicking on the file you downloaded.
- Your lab instructor will supply you with the weighted monochord
apparatus, a sample of which is shown in Figure 1. Ensure that
the string stretches smoothly over the monochord sensor, and does not bunch
up around the monochord edge when the weight is suspended from the string's
end, and shown in Figure 2. It may be helpful to have one lab
partner hold the monochord, and the other partner make measurements.
- Connect the monochord sensor to the audio input on the computer on which
the Pd patch is running.
- Under the Media menu in Pd, select audio ON. This will
begin the recording of audio.
- Have one lab partner gently pluck the string, while the other partner
holds the apparatus. When you see a roughly periodic waveform, click
Pause Display. You may click Begin Display to restart
real-time waveform viewing. A sample of the paused plot you may obtain is
shown in Fig.3.
- Finally, using the x-axis of the paused plot, measure the approximate
distance between either peaks or troughs of the waveform. This will serve as
an estimate of the period of the waveform. From this value, compute the
fundamental frequency of string vibration (see part 3 of the monochord lab assignment to learn
about the relationship between the period and the fundamental frequency). How does this compare with the fundamental frequency you predicted in the previous section?
Figure 1:
Photograph of the weighted monochord apparatus.
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Figure 2:
Photograph showing the weighted end of the apparatus.
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Figure 3:
Pd patch for this lab activity, showing a few cycles of
the waveform obtained from a vibrating string.
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Download weighted_mono.pdf