30/8/2023

Audio is sent via the DAC, digital audio converter on most devices, except for analogue audio formats such as vinyl. Most people spend their entire lives listening to digital audio whether it be through speakers, headphones or earbuds audio has been sent to our ears using digital means. This means that audio must be converted to a signal that can sent to a speaker, which oscillates at the correct frequency to produce a desirable sound. This can be observed via listening in the middle of the signal simply by splicing the cable of headphones and measuring the voltage across it using the oscilloscope.

Equipment

A 1994 20Mhz Goldstar oscilloscope was used to measure the voltage. A cheap pair of $5 earbuds was used to splice and measure the signal and a cheap laptop found during council cleanup was used as a DAC which could play any audio I choose. This allowed me to play sounds from tone generators online and audio clips from YouTube. It should also be noted that I wired my headphones in such a way that the audio is out of phase and therefore when playing out-of-phase audio testers online the concept of phase can be clearly observed and serves as an appropriate model for noise cancelling headphones in the real world.

What I Saw

I saw a variety of waves within waves, superposition. These waves represent the range of frequencies within an audio clip. When playing a pure sound wave a pure Sine wave appeared on the oscilloscope as expected. When playing a variety of waves the waves are superimposed. The changes in voltage represent the displacement of the diaphragm from the speaker from its centre position.