Synthetic sound creation also known as sound synthesis is where sound is created from circiutry or manipulation of code. When its in code its manipulation of either samples or code that creates numbers that get converted through a digital to analogue converter. The numbers represent voltage at a given time. With the voltage changing of a period of time you will get a wave form. This is essentially how music is recorded. Recording sound requires a analogue to digital converter. This records voltage levels over time. The more samples of voltage taken per second the more accurate the wave forms recorded. In analogue sound synthesis wave forms can be created through a feed back loop or with a capacitor that stores electrical energy for a short period of time. The smaller amount of capacity the faster the change in voltage level. In other words if the capacity is decreased this will increase the frequency of waves measured in hertz. The faster the wave rises and falls the higher the pitch you will hear.