At the beginning of the semester a hardware demonstration is shown to the students so that they get a notion of what we are talking about. It is a circuit that plays a little music or a single note from an FPGA on a loudspeaker. In parallel, the output signals are visualized on an oscilloscope. The number of bits used to generate the notes can be modified. This allows to show what's a digital signal, show and hear the meaning of bits and vectors as well as frequency.
The FPGA design can be found at: https://repos.hevs.ch/svn/eda/VHDL/labs/ELN_support.