Modular synthesiser such as this one (Buchla 200e) use electronic signals to output sounds. The sounds they output is a mixture of various signals input that get picked up and fed into the machine. The output becomes input, get amplify, distorted, processed... at the end it become sound and sometimes music.
The tiny electric signal of one output plug, might be a sound. But sometimes it is nothing we can ear. If something picked up from an oscillator is connected to something else though, things start to become interesting.
The operator (read composer) input and output signals to the machine, the intention is music.
Can we input and output signals through the machine with more head and more hands?