Instructions For Setting Sine Waves With FreX & REBS

This is a pretty straight forward task to do. Connect REBS to the computer, run FreX and output a frequency, check the explore option and change the frequency to 500 Hz. Select Sine Wave in FreX, and click the In/Out switch to the In position. Depending on your volume control, you should have an image similar to below. If not, adjust the microphone dial on REBS until you do. If you still can't see a sine wave signal, check the microphone and sound card connector, make sure they a firmly all the way in the connector. On some notebooks, there will be an audio power save utility which is usually defaulted to ON. This needs to be located, usually in the Windows Control Panel and switched to OFF. Otherwise this power saver utility will kill the microphone input signal. On many notebook computers, this utility is called SoundMAX Audio Power Management. Also check Windows Recording folder to make sure the microphone is selected and not muted. To navigate there, open the Windows Control Panel, and double click the Sounds and Audio Devices icon. The Sounds and Audio Devices Properties form will open. Click on the Voice tab. Next click the Volume button in the Voice Recording section. In the Recording Control form that opens up, check the Microphone Select function. Now exit all and start these instructions again from the beginning. Now we have a sine wave as above being displayed, we need to optimise it for maximin output. Turn the computer volume up until the sine wave starts to produce flat tops and bottoms as in the image below. Notice the multiple vertical lines in the spectrum chart, below the oscilloscope. This indicates numerous harmonics are being produced, and the sine wave is no-longer a pure sine wave. We don't want this for sine wave applications (physiological effects). Now, slowly reduce the volume to where the vertical lines in the spectrum disappear and a display similar to below is present. Those small dots in the spectrum are okay and will be an imperfection in the microphone buffer producing the display. It may happen on some computers, and other computers it will not be there. But to easy your mind, below is the display of the same signal with a Digitech 10MHz Oscilloscope. You can see how pure and analogue it is. This signal can now be used for physiological effects. Setting the sine wave in this way will produce about a 10 volt peak to peak signal and can be used in AC or Pulsed DC mode. I personally prefer Pulsed DC mode.