Analog Sound Synthesis on Your Computer

Step 2 Input

Input to the simulator is in the form of a schematic diagram. You select components, place them on the schematic, then wire them together. Once your circuit is complete, you tell the simulator how you want it to simulate the circuit and what sort of output you want.

Take a look at the schematic called resistors.asc. You'll see there is a circuit that includes a voltage source, a pair of resistors, a labeled output node, a ground, and a text command line. Let's look at each one. Now is a good time to open the circuit file linked below.

Ground:
This is the MOST CRITICAL component on your schematic. You MUST have a ground connected to at least one point on your circuit or you will get very strange results from your simulations.

The voltage source:
If you are putting a voltage in a circuit, you need to tell it whether it is AC or DC (or something more complex), what the voltage is, the "internal resistance" of the source, etc. You can enter those parameters by right clicking with the pointer on the source. All you really need is the resistance for simple simulations.

Resistors:
The resistors are pretty easy to understand. Just right-click to set value of resistance. Ignore any other parameters that might be hiding there.

Labeled input and output nodes:
Just names for nodes in the circuit that are user friendly.- use names like "output", "input", etc.

The simulation directive:
the .tran statement tells the simulator how you want the circuit to be simulated. This is a time-domain simulator which means it analyzes the circuit at different points in time. You need to tell it what the maximum time step should be and how long the simulation should run in "circuit-time", not real time. If you tell the simulator to run for 10 seconds of circuit-time and you set the maximum time step to 0.001 seconds, it will analyze the circuit at least 10,000 times (10 sec/0.001 sec) then stop.

When the simulation runs, the voltage at every node in the circuit and the currents into and out of every node will be calculated and saved at each time step. All that info will be available to plot on a display like an oscilloscope screen (time of the horizontal axis, voltage or current on the vertical axis. Alternatively, you can also send the output to a .wav audio file that you can play on a computer, burn to a CD, or convert to mp3 to play on your mp3 player. More on that later...