This is a piece of test equipment that displays voltage fluctuations as graphical waveforms. A ’scope can run at a wide range of frequencies, displaying slowly changing voltages like LFOs or envelopes, or quickly changing voltages like oscillators and noise. Oscilloscopes used to be bulky pieces of external equipment, but now you can get USB scopes that offload the display portion of the job to your computer (I used a BitScope Micro USB scope for the original Learning Modular Synthesis course), or scopes as modules (I use a Mordax DATA for all of my current videos, as well as in my larger personal system).
Similar:
o'scope, 'scope