Manual for the program SpectrumSLC

Program-Files:
The program is a single exe-file that can be started directly on your computer without installation. The only additional file that is needed is bass.dll. It should be in the same directory, where the exe-file is located or in a directory where Windows is searching for dll-files by default.

 

Configure Input:
After starting the program, you should check, which channel of your sound-card is used as input. Open in the menu “Configure”  -> “Input Channel / Volume”. In the window that opens up, you can select the input channel and adjust the volume. You may use “Line-in” or “Microphone” depending on how you have connected the experiment to your sound-card. On default the sum of both input channels (left and right) is used as input signal. In the menu “Configure” -> “Mono / Stereo” you can select a single one (left or right) as input if this is preferred. Please take care that your sound card does not use any filters that may screw-up the input signal.

 

Measure a spectrum:
Choose the start and stop frequencies, the frequency steps in Hz and the time per step in milliseconds. When pressing on the button “Measure” the programs plays a frequency-sweep with a continuously increasing frequency. At same time the input-signal is recorded and analyzed. There are to ways to extract the mean amplitude from the AC-signal. The recommended one is using a fast Fourier transformation (“FFT-Filter on” checked).  This mode is providing a very narrow band-pass filter that makes the signal insensitive to other noise sources. You may display the Fourier-transformation of the current signal in a separate window (see below) to observe how the current signal is processed. The other mode (“FFT-Filter on” not checked) uses the mean amplitude of the current signal directly. You may display the current signal as function of time in a separate window (see below) to check the quality of the signal.
The computer uses the time between two step for drawing the spectrum and for other interrupts. If this time is not sufficient the sweep is stopped internally, rewinded and restarted at the proper position. This, however, needs a lot of extra time. Such a situation is indicated by a little red square in the lower left corner of the main window. If this red square is blinking more or less continuously while taking a spectrum, you should reduce other tasks of the computer or choose a longer “Time per Step”.

The vertical scale in the spectra is an arbitrary scale. The numbers are proportional to the sound amplitude, however, the absolute value depends on the soundcard settings. The signal starts to saturate at values above 100. Take care that you measure in the linear range below 100. A saturation warning is given by a blue bar in the lower left corner of the main window. 

 

Current spectrum:
The program is organized in a way that four different spectra can be handled and displayed simultaneously in different colours. This can be used to compare spectra with each other. All activities like “Measure”,  “Clear Spectrum”, “Fit Spectrum” or “Save Spectrum” refer to the spectrum chosen currently. Use the buttons in the top left corner to choose the index of the “Current Spectrum”

 

Save Data:
The measured data can be saved as an ASCII-file. Go to “File” -> “Save Spectrum”. The Data are saved in two columns with frequency in Hz and amplitude in arbitrary units.

 

Open Data:
To reload data go to “File” -> “Open Spectrum”. The data are loaded into the currently chosen Spectrum (index 1 .. 4).

 

Save as Image:
The currently displayed image can be saved is a graphic file (bmp or jpg format for example). Go to the menu item “File” -> “Save as Image”. This feature can be used by students to create figures for their report easily.

 

Print Image:
The currently displayed image can be printed directly. You can choose the printer settings “File” -> “Printer Setup” and than print the image “File” -> “Print”.

 

Display:
To look at details in a spectrum you can magnify the spectrum with respect to the frequency scale by choosing one of the buttons “normal”, “wide”, “very wide” and “maximal”. The Image is then displayed in a scroll box. In this case, saving and printing of the image refers to the hole image not only to the visible part.

 

View:
With menu item “Change Font”, the size and style of the font can be changed.
With menu item “Change Pen Color”, the colour of the current spectrum can be changed.
With menu item “Line Thickness ”, the with of the lines can be changed.

 

Life FFT of Microphone  Signal:
The menu-item “Windows” -> “Life FFT of Microphone Signal” opens a separate window that displays the Fourier-transformation of the current input signal from the microphone (Amplitude as function of frequency). If “FFT-Filter on” is checked the band-pass is indicated by gray/white background.

 

Life Image of Microphone Signal:
The menu-point “Windows” -> “Life Image of Microphone Signal” opens a separate window that displays the current input signal from the microphone as function of time.

 

Measure a wave function:
Click with the left mouse button exactly on the position (frequency) in the spectrum, where you want to measure the wave function. The chosen frequency is played for 5 seconds  Then go to the menu-item “Windows” -> “Measure Wave Function”.  The “Angle between hemispheres” refers to the angle on the scale mounted at the top hemisphere. This angle is called alpha in the manual. In the case of a spherical resonator “Lifted degeneracy” must not be checked. The angle alpha is converted correctly into the polar angle theta as described in the manual. In the case of lifted degeneracy or experiments with the molecule the checkbox “Lifted degeneracy” must be checked. In this case the angle is not converted and represents the azimuthal angle phi. Rotate the hemispheres to the correct angle and click on “Measure value”. A single amplitude is measured at the chosen angle with the frequency chosen before (When starting the measurement, the first data-point is not displayed - continue and you see how it works). Continue this procedure for all angles 0-180°. The amplitude as function if angle theta or phi is displayed in blue or green, respectively. The figure is a radial plot. You may complete the figure by symmetry and show the polar grid by checking the checkboxes.  The data can be saved as ASCII-file and the current image can be saved or printed. The ASCII-data are saved in a two-column format with angle and amplitude in the first and second column, respectively. In case of saturation of the signal a warning is given by a blue bar blinking up next to the button "Measure value". 

 

Fit:
Spectra can be fitted by a maximum of 8 peaks. The peak shapes that are used can be found in the manual. To open the Window for peak fitting choose the spectrum that you want to fit as the "Current Spectrum" and go to “Windows” -> “Fit”. The spectrum is shown in a separate window. Move your mouse to the top of the first peak and click the left mouse button. This puts the first peak to its position. Use the mouse wheel to adjust the peak width. Then choose “2. Peak” in the top left corner of the window (you may instead click the right mouse button), move to the next peak and click on the left mouse button. Continue for the other peaks.  For the shape of the total spectrum the phase of the (complex) peaks with respect to each other is important. The phase of each peak can be changed by the slider on the left. If you want to fit only part of the total spectrum you may specify the “Fit Range”. Then press “Start Fit” and wait until the spectrum has been fitted. In case that your starting parameter were not good enough you have to adjust the peaks better before starting the automatic fit. The fitted parameter can be read on the left for each peak and can be saved as ASCII-File.