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Procedure

  1. First, download the Pd patch for this lab. Open the Pd patch in Windows by double-clicking on the file you downloaded.

  2. 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.

  3. Connect the monochord sensor to the audio input on the computer on which the Pd patch is running.

  4. Under the Media menu in Pd, select audio ON. This will begin the recording of audio.

  5. 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.

  6. 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.
\includegraphics{figures/whole_device.eps}

Figure 2: Photograph showing the weighted end of the apparatus.
\includegraphics{figures/weighted_end.eps}

Figure 3: Pd patch for this lab activity, showing a few cycles of the waveform obtained from a vibrating string.
\includegraphics{figures/mono_patch.eps}


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Download weighted_mono.pdf

``Weighted Monochord Lab Activity'', by Ryan J. Cassidy, Edgar J. Berdahl, and Julius O. Smith III,
REALSIMPLE Project — work supported by the Wallenberg Global Learning Network .
Released 2008-06-05 under the Creative Commons License (Attribution 2.5), by Ryan J. Cassidy, Edgar J. Berdahl, and Julius O. Smith III
Center for Computer Research in Music and Acoustics (CCRMA),   Stanford University
CCRMA