Almost all modern computers have a sound card, either on the motherboard or on an expansion card. This card is used to convert digital data into analogue sound signals. You may wonder if such a card could be used as a function generator. This is certainly possible, although the limitations of sound cards have to be kept in mind. There are various programs available that do this, but that isn't as much fun and educational as writing your own Delphi program that generates user-defined signals.