(Signal Processing for Experimental Chemistry Teaching and Research/ University of Maryland) is an interactive, graphics-oriented signal processing program which enhances and extracts additional information from digitized signals generated by measurement instruments which produce "spectral" or time-series data (y values at equally-spaced x intervals). The program implements many digital processing operations that can enhance the information content of instrument signals, for example by reducing noise, improving resolution, compensating for instrumental artifacts, testing hypotheses, and decomposing a complex signal into its component parts. The program provides a convenient environment in which to explore these techniques interactively and visually, and has applications both in instruction and as a research tool.
S.P.E.C.T.R.U.M. was written in Turbo Pascal by Prof. T. C. O'Haver, Department of Chemistry and Biochemistry, University of Maryland, College Park, MD 20742. Bitnet toh@umd2.umd.edu
ABBREVIATED INSTRUCTIONS FOR EXPERTS:
1. To select a window:
Click on the desired window.
or pull down the Window menu and choose Select Signal 1, etc.
or press Command-1, or -2 or -3 or -4.
2. To load a signal file from the disk into a window:
a. Select the desired window.
b. Select Open Y file... (Command-O) or Open XY file... from the File menu or press Command-O.
c. Double click on the desired file.
3. To move (copy) a signal from one window to another:
a. Select the window of the signal to be moved.
b. Select Copy from the Edit menu, or press Command-C.
c. Select the window to receive the signal.
d. Select Paste from the Edit menu, or press Command-V.
e. Note: This operation replaces the signal in the receiving window.
4. To perform an operation involving a single signal (e.g. normalize, derivative, second derivative, smooth, resolution enhancement, integrate, peak area, interpolate, zero fill, power spectrum, auto correlation, Fourier filter, add constant, multiply by constant, rotate, reverse x-axis, extract subset of points, reciprocal, log, standard deviation, absolute value, square, square root, and all the operations in the Curve fit menu.):
a. Select the window of the desired signal
b. Select the desired operation from the Transformation, Window, Math or Curve Fit menu.
c Note: The resulting signal replaces the selected signal, except for the Peak area, standard deviation, and Curve fit operations, which report results based on, but do not modify, the signal.
d. Note: The operations in the Curve fit menu place the fitted curve onto the clipboard (replacing the former clipboard signal) from whence it can be pasted into another window if desired.
5. Operations that involve two signals (e.g. convolution, deconvolution, cross correlation, concatenate, superimpose, and add, subtract, multiply, and divide signals) operate between the selected signal and the “clipboard” signal. A signal is placed into the clipboard by the Copy command.
a. Select the window of the first signal.
b. Select Copy from the Edit menu, or press Command-C.
c. Select the window of the second signal.
d. Select the desired operation from the Transformation, Window, or Math menu.
e. Note: The resulting signal replaces the signal in the second window. The clipboard signal remains unchanged.
6. Fourier Transformation operates in a special way, using pairs of windows to display the real and imaginary parts. The number of points must be an integral power of 2 (i.e. 65, 128, 256, 512, 1024).
a. Place the signal whose Fourier transformation is to be obtained in window 1 (or window 3).
b. Select Forward Fourier Transform form the Transformation window.
c. The real part of the transform will replace the original signal in window 1 (or window 3) and the imaginary part of the transform will replace the signal in window 2 (or window 4).
Inverse transformation works similarly:
a. Place the real part of the signal whose inverse Fourier transformation is to be obtained in window 1 (or window 3).
a. Place the imaginary part of the signal whose inverse Fourier transformation is to be obtained in window 2 (or window 4).
c. Select Inverse Fourier Transform form the Transformation window.
d. The real part of the inverse transform will replace the original signal in window 1 (or window 3) and the imaginary part of the inverse transform will replace the signal in window 2 (or window 4).
Note that, since the forward transformation assumes that the signal is real, the inverse transformation of its Fourier transform will yield a zero imaginary part, except for numeric round-off errors.
7. To change the line style of a signal:
a. Select the desired signal.
b. Pull down the Line menu and select plain black line, dots, or connected dots.
8. To save a signal to the disk:
a. Select the desired signal.
b. Select Save as Y file... (Command-S) or Save as XY file... from the File menu.
c. Type in the desired file name and select the target disk and folder in the usual way.
d. Click the Save button, or press the return key.
9. To print a signal:
a. Select the desired signal.
b. Select Print... from the File menu, or press Command-P.
c. Click in the desired print quality, in the usual way.
d. Click the Print button, of press the return key.
10. To quit SPECTRUM and return to the Finder: Select Quit from the File menu or press Command-Q.
