Does a relay "click" if there's no one to hear it?

Switches "switch". Relays "click". (Spoiler alert; even if there's no one to witness). Mechanical or quasi-mechanical switches are antiquated devices in a modern world. There are other alternatives that make no sound at all. Switches that make no sound are called analog switches. They are typically MOSFET based and their types vary to the same degree as their mechanical counterparts: cheap ones, expensive ones, good sounding ones, bad sounding ones. Again, it's all up to the skill of the designer. Traditional bipolar transistors don't work well for analog switches. Digital, yes. Analog, no. This is because bipolars have diodes that distort low-level AC signals. MOSFETs, on the other hand, are near-perfect switches. To make an analog switch you can use a single MOSFET but typically you use two. One in series, the other in shunt. These switches are low cost and excellent sounding. Not as good as the finest gold, rhodium, or silver tipped relays, but damned close. We use a special brand of MOSFET analog switch in all our entry and midlevel analog audio products. Relays are used in our highest end analog audio products like the BHK series. So wrapping this up there are three types of input selectors in use: mechanical switches, relay switches, analog switches. The latter two are easy to control via a remote. Tomorrow we look at the biggest challenge of them all, the volume control.