Control Testing of Guitar Sound and Sustain

In order to analyze the differences between the spruce and composite material's effects on the soundboard a qualitative measure of sustain is necessary. However the sustain may vary depending on the force applied to the string. Playing the string manually would not then be an appropriate means of measuring the sustain. A simple mechanical device was made to ensure that the force of each pluck of the string was the same. The device is a hollow wooden box that is placed vertically lengthwise, with two slits on the opposing horizontal sides which act as a track for a weighted center piece which slides up and down and holds a guitar pick. The device can be seen in the photos below. 

Strumming Device

 This instrument allowed for the playing of a string at a constant force. The next step involved finding software which would record a sound and display a graph of its amplitude over time. (Frequency is not needed as the guitar strings are always tuned to the same frequencies). The freeware program Audacity was a prime choice for this task as it features the graph and allows it to be zoomed and manipulated. A sample of this graph is shown below.

First test of the high E String

By plotting the maximum value of each oscillation as a function of time, a linear regression model can be applied to the points to find where the amplitude reaches approximately zero. The time at which the amplitude is zero will be used to measure the sustain. That value will be averaged over each test of a given string and compared to the value found for the other soundboard to indicate the changes in sustain.