The conversation between human and AI assistant.
[|Human|] Classify the following based on the category of signals they use.
radio waves, television waves, sound waves, Computers, Digital Phones, Digital pens
[|AI|] Analog signal- radio waves, television waves, sound waves
Digital signal- Computers, Digital Phones, Digital pens
[|Human|] 
Classify the following based on the category of signals they use.
radio waves, television waves, sound waves, Computers, Digital Phones, Digital pens