You can easily observe the audio signals coming from an MP3 player or radio if you have an oscilloscope. The oscilloscope will reveal the complex frequencies and wave shapes of audio signals from music, speech and other sounds. If you use a “Y” adapter cable, you can hear the music and watch the oscilloscope at the same time. If you have familiarity with the oscilloscope’s controls, this demonstration takes only a few minutes to set up.
Turn on the oscilloscope. Set its horizontal sweep speed to 1 millisecond per division. Set the vertical input control to 1 volt per division. Set the input coupling to AC.
Plug the “Y” adapter into the MP3 player or radio earphone jack. Plug the headphones into one of the jacks in the “Y” adapter. Plug the mini phone cable into the remaining “Y” adapter jack. Put the headphones on and find music on your player or radio. Adjust it to moderate volume.
Examine the unconnected end of the mini phone plug cable, and you’ll notice it has three metal areas separated by rings of black insulator. Clip the oscilloscope’s input probe onto the tip of the mini phone plug. Connect the probe’s grounding clip to the area on the metal plug nearest the base. You should see the sound waves from the music displayed on the oscilloscope.
Vary the oscilloscope’s sweep speed to get a better look at waves of different frequencies. Adjust the vertical input control or the player’s volume control if the waves appear too large or small on the oscilloscope screen. The “Y” adapter should have one mini stereo plug and two mini stereo jacks.