The following samples were collected using a CBL and TI-82 calculator. The electronic keyboard was collected at a teacher's house, the upright during a summer workshop and the baby grand during a fall convention. Though the CBL - calculator files don't have many points, the method is certainly portable.

Sample size - 99 points

 Plot of a baby grand piano, an upright piano and 
an electronic keyboard set to piano playing Middle 'C'




 Fast Fourier Transform Plot for the above signals
Note the extra frequency in the keyboard