Analog Sound Synthesis on Your Computer

Step 6 Bells, drums, cymbals, plucked strings

Bells, drums, cymbals, and plucked strings are all percussive. They have a relatively fast rise time and an exponential decay time. Those are easy to create using sine and behavioral voltage sources combined with some simple circuits.

Look at the schematic "bell_drum_cymbal_string.asc". The pulsed voltage sources with the resistor, capacitor and diode create the fast rise and slow exponential decay waveforms needed. Those output voltages modulate the outputs of behavioral sources set up as random noise or sine wave sources. When the pulsed source voltage rises it quickly charges the capacitor. The capacitor then discharges through the resistor. The diode keeps the voltage source from discharging the capacitor when the source voltage is at zero. Bigger resistor values increase the discharge time. You can specify the rise time of the pulsed source - the cymbal is a nise source with a very fast rise time. The drum is also a noise source that operates at lower frequency and has a slower rise time. The bell and string use sine wave sources that are modulated by pulsed sources too. The bell operates at higher frequency and has a faster rise time than the string.

Run the simulation and listen to the result. Note that the drum appears in both channels while all the other sounds are either right or left channel. The two resistors at the drum output are responsible for putting the sound into both channels.