Frequently asked questions about the Program SpectrumSLC.exe

I do not have any signal, what can I do?

You should plug of the instrument from the sound card and use the sound card with regular speakers and a microphone to test if your sound card is working correctly. After starting the program SpectrumSLC and pressing the start button you should hear a sweep that needs about 50 second to sweep from 100 to 10000 Hz. If you does not hear anything read the question "I do not have an output signal".

Uncheck the checkbox "FFT-Filter on" and knock on the microphone while a measurement is running. In the spectrum displayed on the screen spikes should appear whenever you knock on the microphone. If nothing is happening read the question "I do not have an input signal". You may also use any other program to record sound from the microphone to check if input is working.

 

I do not have an output signal, what can I do?

Windows provides the possibility to switch of the output and to adjust the loudness of the output. You should look up if output is switched on and loudness is set to a useful level. You may also check if the sound-card drivers are installed correctly and if the speaker is plugged to the correct connector. You may check with a regular program like Windows Media Player if output is working correctly.

 

I do not have an input signal, what can I do?

In the menu of the SpectrumSLC go to "Configure" -> "Input channel / Volume" In the box "Select input channel" you have the choice between all availible input types that your sound card is providing. If you have connected a microphone directly to the sound card you should choose "Microphone", if you are using an electrical AC-signal in a range of Vpp = 2V at the input of the sound card then choose "Line-in". You can adjust the input volume by the slider. Press "OK" and check again if the input signal is working. 

 

How can I check the quality of my input signal?

Open the window "Life FFT of the Microphone Signal" and the window "Life Image of the Microphone Signal". In these windows you can observe continuously the microphone signal as function of frequency and as function of time, respectively. These windows are very helpful to check if there is noise on the signal or if there are problems with filters that some sound-cards have switched on by default. While sweeping a spectrum there should be a single peak at the current frequency sweeping from left to right. If the FFT-filter is switched on, the gray/white background indicated the frequency-window that is used for data-recording. The single sharp peak during sweeping a spectrum should be located within the small white window. If there is all the time a sharp peak dominating the FFT-spectrum that does not sweep at all, read the next question about acoustic feedback. (When clicking with the left mouse button in the spectrum a 10 second long sound with the clicked frequency is produced. This is normal and should not be mixed up with an acoustic feedback.)

 

I get an acoustic feedback when I am closing the resonator, what can I do?

Some cheap sound cards have a significant electrical crosstalk between the output signal and the input signal. If the speaker and microphone are located in a closed resonator a feedback-loop builds up and a whistle is produced that has a constant frequnecy independently of the sweeping frequency. It can be identified best by opening the window "Life FFT of the Microphone Signal". If you have this problem it is recommended to use another sound card.

 

There is a little red box allways blinking in the lower left corner of the main window, what is that?

This red box indicats that the sweep has stopped, rewinded and restarted at the current position of the spectrum. If it is blinkind only from time to time it is no problem, if it is blinking continuously, the computer is to slow to keep up with the speed of the sweep that you have chosen. You should increase the "Time per Step" to make the sweep slower until the red box does not blink at all during a sweep or is blinking only from time to time.

If you are doing any action during a sweep like opening another window, the sweep is stopped and restarted at the correct position. In this case the red box is blinking once, which is normal and does not matter.  

 

There is a little blue bar blinking up in the lower left corner when sweeping over high peaks. What is this?

This is a warning for saturation of the signal. At a signal level above 100 the analog-to-digital converter runs into saturation. In this case the signal is no longer proportional to the sound amplitude. Saturation is also indicated by measurements of the wave function. In this case the blue bar is blinking up close to the button "Measure value".