The image is a plot of the data measured by the probe on the scanning machine. The probe measures and reads out the height of a surface in its range at 180 points on a line 1.8mm wide. This plot results from measuring a 1.8mm line on a cylinder. The groove intersects the line several times as it winds around the cylinder and so shows up as several crescent shaped dips in the height of the surface.
A view of a sample data set. A computer algorithm has created an image from the height data collected during the optical scan. The cylinder is displayed at the top left as if it has been opened up and flattened out. The height of the cylinder surface corresponds to the gray-scale value. Black is deepest and white is highest. The analysis software has also found the bottom of the groove and traced it in blue. Next the algorithm will look at the data along the blue lines, take the derivative between points to calculate the speed of the needle along that line and calculate the sound.
A View of the computer program used to read and display optical scans. The program shows an overview of a large data set which can be a small portion of a cylinder, or an entire cylinder and a detail of the cylinder surface. The software also displays a point by point profile of the data that was collected.
This method is meant to illustrate how data collection works for a cylinder. During acquisition, individual measurements of the height at 180 points along a line are taken in quick succession, at slightly different positions, as the cylinder rotates, and then stitched together in analysis software.
The image shows the frequency content of the same cylinder digitized through the traditional method of playback, a hard stylus, (shown in blue) and through the optical method (shown in purple). The stylus transfer has louder low frequency noise and audio at high frequencies is heavily attenuated, with several peaks resulting from unknown artifacts. The optical method has an even frequency responds and captures audio at higher frequencies without rolling off.